Evaluation of Factors Influencing Grit Use by Birds James Paul Gionfriddo Iowa State University

Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations

1994 Evaluation of factors influencing grit use by birds James Paul Gionfriddo Iowa State University

Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Ecology and Evolutionary Biology Commons, Forest Sciences Commons, Natural Resources and Conservation Commons, Natural Resources Management and Policy Commons, and the Zoology Commons

Recommended Citation Gionfriddo, James Paul, "Evaluation of factors influencing grit use by birds " (1994). Retrospective Theses and Dissertations. 11259. https://lib.dr.iastate.edu/rtd/11259

This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS

This mamiscript has been reproduced from the microfihn master. UMI films the text directly firom the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.

The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.

In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.

Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book.

Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order.

A Bell & Howell Information Company 300 North Zeeb Road. Ann Arbor. Ml 48106-1346 USA 313/761-4700 800/521-0600

Order Number 9518S82

Evaluation of factors influencing grit use by birds

Gionfriddo, James Paul, Ph.D.

Iowa State University, 1994

UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106

Evaluation of factors influencing grit use by birds

by

James Paul Gionfriddo

A Dissertation Submitted to the

Graduate Faculty in Partial Fulfillment of the

Requirements for the Degree of

DOCTOR OF PHILOSOPHY

Department: Animal Ecology Interdepartmental Major: Ecology and Evolutionary Biology

Approved:

Signature was redacted for privacy.

In Charge of Major Work Signature was redacted for privacy. For the Interdepziraiental Major Signature was redacted for privacy. For the Major Depnent ent Signature was redacted for privacy. 1 luate College

Iowa State University Ames, Iowa

1994 11

DEDICATION

To Dad iii

TABLE OF CONTENTS Page

CHAPTER 1. GENERAL INTRODUCTION 1

Dissertation Organization 3

Literature Cited 3

CHAPTER n. A SALINE FLUSHING TECHNIQUE FOR DETERMINING THE DIET OF SEED-EATING BIRDS 5

ACKNOWLEDGMENTS 9

LITERATURE CITED 9

CHAPTER in. GRIT USE BY HOUSE SPARROWS: EFFECTS OF DIET AND GRIT SIZE 11

ABSTRACT 11

INTRODUCTION 12

METHODS 14

GRTT USE BY FREE-RANGING HOUSE SPARROWS 14

EXPERIMENTS 16

Grit Size and Diet Experiments 17

Grit Retention Experiments 18

RESULTS 20

GRIT USE BY FREE-RANGING HOUSE SPARROWS 20

GRTT SIZE EXPERIMENT 21

DIET EXPERIMENT 22

GRTT RETENTION EXPERIMENTS 22

DISCUSSION 24 iv

ACKNOWLEDGMENTS 29

LITERATURE CITED 30

CHAPTER IV. EFFECTS OF SURFACE TEXTURE AND SHAPE ON GRIT SELECTION BY HOUSE SPARROWS AND NORTHERN BOBWHITES 37

ABSTRACT 37

INTRODUCTION 37

METHODS 38

RESULTS 41

DISCUSSION 42

ACKNOWLEDGMENTS 43

LITERATURE CITED 44

CHAPTER V. GRIT COLOR SELECTION BY HOUSE SPARROWS AND NORTHERN BOBWHITES 49

ABSTRACT 49

INTRODUCTION 50

METHODS 52

Initial Experiments 52

Colored Food Experiments 54

RESULTS 55

Initial Experiments 55

Colored Food Experiments 57

DISCUSSION 58

MANAGEMENT IMPLICATIONS 61 V

ACKNOWLEDGMENTS 62

LITERATURE CITED 62

CHAPTER VI. GRIT-USE PATTERNS IN NORTH AMERICAN BIRDS: THE INFLUENCE OF BODY SIZE, DIET, AND SEX 69

METHODS 69

RESULTS 71

DISCUSSION 73

ACKNOWLEDGMENTS 76

LITERATURE CITED 76

CHAPTER Vn. A REVIEW OF GRIT USE BY BIRDS 87

INTRODUCTION 87

FUNCTIONS OF GRTT USE 91

CHARACTERISTICS OF GRIT 96

Grit Size 96

Grit Shape 98

Grit Color 99

Grit Composition 102

AMOUNT USED 103

RETENTIONTIME 107

GRIT SUBSTITUTES 110

Pesticide Granules 112

Lead Shot 113

SUMMARY 114 vi

ACKNOWLEDGMENTS 116

LITERATURE CITED 116

Appendix 1. Sources of information on grit use by wild birds 143

Appendix 2. Scientific names of avian spedes/subspedes whose common names appear in text, tables or Appendix 1 156

CHAPTER Vin. GENERAL CONCLUSIONS 162

ACKNOWLEDGMENTS 166 1

CHAPTER I. GENERAL INTRODUCTION

Avian digestion and the function of the gizzard have long been of interest to scientists and to those who study or raise birds. The value of the grit particles found in birds' gizzards has been recognized for more than two centuries (Spallanzani 1783 [dted in Westerskov 1965]). Relatively little is known, however, about the dynamics of grit use or about the factors that influence the selection of grit particles by birds. Very little experimental work has been done to examine grit use by wild (non-domesticated) birds. Moreover, much of the available published information on avian grit use is widely scattered in the literatures of avian biology, wildlife management, and poultry science. No comprehensive synthesis of this material exists.

In addition to its importance to the study of avian digestion and nutrition, an understanding of the dynamics of avian grit use also is relevant to the problem of avian mortalities resulting from the use of granular pesticides. These pesticides are applied to millions of acres of agricultural lands in the United States each year (U.S. Dep. Agric. 1992), and many are highly toxic to birds (Balcomb et al. 1984, Hill and Camardese 1984). One potential route of avian exposure to pesticide granules is their consumption as grit (Best and Fischer 1992). The extent to which the physical characteristics of pesticide granules are similar to those of natural grit particles may strongly influence the probability (JKat birds ingest the granules. An understanding of the particle characteristics that influence avian responses could be useful in designing pesticide granules less likely to be consumed in lethal doses by birds.

This dissertation presents the results of a wide range of aviary experiments that were conducted with House Sparrows (Passer domesticus^ and Northern Bobwhites fColinus virginianus) to examine numerous aspects of avian grit use. Before the experiments could be 2 conducted, however, a means of humanely removing all grit from the gizzards of live, granivorous birds was needed. Chapter n describes a new gizzard-flushing technique developed to meet this need. Although similar procedures have been successfully used to void the stomachs of insectivorous birds (e.g.. Ford et al. 1982, Major 1990), this is the first successful application of gizzard flushing in granivorous, passerine birds.

Factors that influence avian grit use include the birds' diet and the physical characteristics of grit, such as particle size. Chapter HI reports the results of an evaluation of the influence of diet and grit size on grit use by House Sparrows. This analysis is based on the characteristics of grit found in the gizzards of free-ranging birds and on the grit-use responses of captive birds maintained on different diets or given access to grit of different sizes. Among the other characteristics that may influence grit use by birds are particle surface texture, shape, and color.

Chapter IV presents the results of aviary experiments designed to determine if birds prefer grit particles with certain surface textures/shapes when given a choice of two grit types.

Color vision is highly developed in birds, and particle color may strongly affect grit selection. The relative conspicuousness of various grit particles to birds may be influenced by color in two ways. Some colors may be inherently conspicuous to birds, regardless of context (Sillen- Tullberg 1985, Roper and Cook 1989, Roper 1990), but conspicuousness also may depend on the degree of contrast with the background (Gittleman and Harvey 1980, Gendron 1986). Responses to colored grit also may be influenced by the colors of the foods birds consume. The objective of the research reported in Chapter V was to test the effects of soil background color and food color on the selection of colored grit by House Sparrows and Northern Bobwhites.

A summary of the results of an analysis of the grit found in the gizzards of 1,440 North

American birds is presented in Chapter VI. This investigation expands upon earlier work that focused on avian species that use midwestem comfiields during the breeding season (Best and

Gionfriddo 1991). Data from the 1,440-bird sample are used to test hypotheses regarding the factors that influence grit use. The findings then are compared with those of previous research.

Chapter Vn provides a comprehensive synthesis of the available published information on grit use by birds. It reviews relevant material from the fields of avian biology, wildlife management, and poultry science, and presents an organized overview of the current state of knowledge of avian grit use. Finally, it furnishes an extensive, tabular compilation of sources of information on grit use by wild birds, including a summary of the nature of the information each source provides.

Dissertation Organization

This dissertation consists of eight chapters, including a general introduction (Chapter I) and a general conclusion (Chapter Vni). Each of the six main chapters (II-VII) was prepared separately as a scientific paper to be submitted to a professional journal for publication. Louis B.

Best is the senior author of one paper (Chapter IV) and is a junior author of the other five papers.

Bret J. Giesler is a junior author of one paper (Chapter II). Each paper follows the format and style recommended by the journal to which it was (or will be) submitted.

Literature Cited

Balcomb, R., R. Stevens, and C. Bowen H. 1984. Toxicity of 16 granular insecticides to wild-caught

songbirds. Bull. Environ. Contam. Toxicol. 33:302-307.

Best, L. B., and D. L. Fischer. 1992. Granular insecticides and birds: factors to be considered in

understanding exposure and reducing risk. Environ. Toxicol. Chem. 11:1495-1508. Best, L. B., and J. P. Gionfriddo. 1991. Characterization of grit use by cornfield birds. Wilson

BuU. 103:68-82.

Ford, H. A,, N. Forde, and S. Harrington. 1982. Non-destructive methods to determine the diets

of birds. Corella 6:6-10.

Gendron, R. P. 1986. Searching for cryptic prey: evidence for optimal search rates and the

formation of search images in quail. Anim. Behav. 34: 898-912.

Gittleman, J. L., and P. H. Harvey. 1980. Why are distastefulprey not cryptic? Nature 286:149-

150.

Hill, E. P., and M. B. Camardese. 1984. Toxicity of anticholinesterase insecticides to birds:

technical grade versus granular formulations. Ecotoxicol. Environ. Saf. 8:551-563.

Major, R. E. 1990. Stomach flushing of an insectivorous bird; an assessment of differential

digestibility of prey and the risk to birds. Aust. Wildl. Res. 17:647-657.

Roper, T. J. 1990. Responses of domestic chicks to artificially coloured insect prey: effects of

previous experience and background colour. Anim. Behav. 39: 466-473.

Roper, T. J., and S. E. Cook. 1989. Responses of chicks to brightly coloured insect prey.

Behaviour 110:276-293.

SillCT-Tullberg, B. 1985. The significance of coloration per se, independent of background, for predator avoidance of aposematicprey. Anim. Behav. 33:1382-1384.

Spallanzani, L. 1783. Experiences sur la digestion de I'homme et de differentes esp&ces d'animaux. Barthelemi Chirol, Libraire, GenSve. [Cited in Westerskov 1965.] U.S. Dep. Agric. 1992. Agricultural chemical usage: 1991 field crops survey. U.S. Dep. Agric.,

Econ. Res. Serv., Washington, D.C.

Westerskov, K. 1965. Utilisation of grit by pheasants in New Zealand. New Zealand Dep.

Internal Affairs Wildl. Publ. No. 65. 31 pp. 5

CHAPTER n. A SALINE FLUSHING TECHNIQUE FOR DETERMINING THE DIET OF SEED-EATING BIRDS

A paper accepted for publication in The Auk

James P. Gionfriddo, Louis B. Best, and Bret J. Giesler

Stomach flushing has been used to determine the diets of many avian species. It has been widely used to sample the food habits of large, hardy birds such as penguins (Randall and

Davidson 1981, Home 1985, Gales 1987) and other seabirds (Wilson 1984, Ryan and Jackson 1986,

Wilson et al. 1989). Applications of stomach flushing to smaller birds generally have been limited to nongranivorous species. Brensing (1977; cited in Ford et al. [1982]) used warm tap water forced through plastic tubing to flush the crops of more than 2,100 migrant passerines of 35 species

(mostly insectivores), with only one mortality. Ford et al. (1982) used a similar procedure to

recover food from crops and, sometimes, gizzards of 157 passerines (28 insectivorous and honey- eating species). Although 13 birds required reflushing, all birds eventually regurgitated some of

the stomach contents, and no mortalities occurred. Zach and Falls (1976), however, reported heavy

mortality of Ovenbirds (Seiurus aurocapillus^ when saline flushing was attempted. Moody (1970)

described a saline flushing technique for insectivorous birds, in which gizzard contents were

intentionally forced out through the cloaca. This method was used to void the digestive tracts of

72 swallows, with 8% mortality. Moody's attempts to use the method on granivorous birds were

unsuccessful because the muscular gizzards impeded the flow of the saline solution. When

Laursen (1978) used this method to flush the digestive tracts of 396 migrant passerines, 14 birds

died during flushing, and the flushing removed only half of the initial stomach contents.

Our analyses of grit use by captive House Sparrows fPasser domesticus) (Gionftiddo and 6

Best, unpubl. data) required a method of removing all grit from the gizzards of live birds. We developed a saline flushing technique that enables researchers to recover the food and grit in gizzards of live granivorous birds. Although our method was used in the laboratory, it can be adapted for use in the field. The procedure requires two workers and involves anesthetizing the birds and allowing their recovery before they are released into the wild or used in ejqjeriments. It is highly efficient in voiding the gizzard and has a low mortality rate. We used the method only with House Sparrows, but believe that, with minor modification, it would be effective with other avian granivores with well-developed, muscular gizzards.

Before flushing the gizzard, we anesthetized each bird by injecting it with a mixture of ketamine hydrochloride (Vetalar: Fort Dodge Laboratories, Fort Dodge, lA; diluted to 10 mg/ml) and diazepam (Valium: Elkins-Sinn, Inc., Cherry Hill, NJ; 5 mg/ml). Diazepam reduced wing fluttering and facilitated recovery from ketamine hydrochloride. For each bird, the anesthetic was prepared by drawing 2-3 drops of diazepam into a 1.0-cc plastic, disposable syringe equipped with a disposable (26 gauge, 3/8 inch) hypodermic needle and then reinjecting the diazepam into its vial, leaving a tiny residue (< 1 drop) in the syringe. Ketamine hydrochloride (0.15 cc) was then dravra into the syringe and mixed with the diazepam. The mixture then was injected into the bird's pectoral muscle, and the bird was restrained or placed in a holding cage for 2-3 min to allow the drugs to take effect.

To flush the gizzard, we used a 10-ml Cornwall syringe pipet (Thomas Scientific,

Swedesboro, NJ) with a ball-tipped, straight intubation needle (18 gauge, 7.6 cm long). The bird was placed on its back, its head extending over the edge of the table or work surface. The tip of the intubation needle was placed in the bird's mouth and then carefully passed through the esophagus to the gizzard. This process was facilitated by gently holding the bird's head and 7 slightly stretching its neck. We sometimes had to delicately maneuver the tip of the intubation needle to enter the opening to the gizzard. The syringe pipet and the bird were then carefully raised to a vertical position, with the bird's beak pointing downward. The syringe pipef s plunger was then depressed 20 times to pump 30 cc of saline solution (0.9% sodium chloride irrigation,

USP; Travenol Laboratories, Inc., Deerfield, IL) from a nearby bottle to the gizzard, in 1.5-cc injections. After the first 10 injections, we paused for 15-30 sec to make certain that the bird was not having difficulty breathing. Gizzard contents were forced out through the esophagus and mouth by hydraulic pressure and gravity. A funnel with filter paper was placed below the bird to recover grit and food flushed from the gizzard. If the bird showed signs of having inhaled the saline solution (gasping, sputtering), flushing was stopped temporarily to allow recovery. Usually a 1-min rest was sufficient. When flushing was completed, the bird was placed in a paper bag or a holding cage for 0.5 - 2 hr to permit recovery from anesthesia. Most birds recovered fully in < 1 hr.

The effectiveness of the saline flushing technique was validated in two ways. In developing the method, we tested several combinations of injection volume (1.0,1.5, or 2.0 ml), number and timing of injections (5 injections - pause - 5 injections, 10 consecutive, or lO-pause-10), and total injected volume (10,15, 20, 30, or 40 ml). For each combination, the gizzards of > 10

House Sparrows euthanized 1 hr after flushing were removed, and their contents examined with a microscope. Material that had been flushed from each of these gizzards and collected also was examined. All procedures we tested that had total injected volumes > 15 ml flushed nearly all grit and food particles from gizzards. Procedures incorporating the "10 injections - pause -10 injections" protocol had the combined advantages of a large number of injections, a large total injected volume, and a low incidence of birds' having breathing difficulties. The only procedure tested that achieved 100% removal of all food and grit particles was flushing gizzards with 30 ml of 8 saline solution delivered as 10 injections - pause -10 injections (at 1.5 ml/injection). We selected this as the most efficient and humane of &e procedures that we tested. The saline flushing technique also was validated incidentally in many of our grit-use experiments with captive House

Sparrows. We flushed the gizzards of birds before experiments in which the birds were given access to one or more types of "experimental" grit. When gizzard contents were examined after the birds were euthanized at the ends of these experiments, particles of "natural" grit picked up by the birds before capture and not removed by the flushing procedure were rarely found (Gionfriddo and Best, unpubl. data).

Since its development, we have used this technique to void the gizzards of 974 House

Sparrows. Its advantages include the ability to thoroughly flush all grit and food particles from the gizzard by repeatedly injecting a metered volume of solution. Diet and grit analyses may be seriously biased if the gizzard contents are not completely voided. The syringe pipet can be adjusted to deliver any volume from 0.5 - 10.0 cc per injection and, with intubation needles available in various lengths, can accommodate birds of different sizes. Another major advantage of stomach flushing methods in general is their nondestructive nature. Birds may be processed and released, or sampled repeatedly in experiments. Recaptures and resightings of treated birds suggest that there are no lasting ill effects of stomach flushing (Moody 1970; Ford et al. 1982;

Gionfriddo and Best, unpubl. data).

Several limitations are associated with the use of this saline flushing method. In our work with House Sparrows since the development of the technique, mortality occurred in 80 (8.2%) instances, either during flushing or within 24 hr, usually resulting from inhalation of saline solution. Many (26) of these mortalities occurred during a 2-day period when we used the method outdoors during relatively cold (<10° C) weatiKer. Hypothermia may have contributed to the 9 unusually high mortality rate (22.6%). Twelve birds were killed when the ball-tipped intubation needle punctured the esophageal or proventricular wall. No known anesthetic overdoses occurred.

Saline flushing caused gizzard contents to be forced out through the cloaca (as in Moody's [1970] method), rather than the mouth, in 26 birds. Other limitations associated with saline flushing include biases associated with differential digestive rates for various food items and the identification of fragmented food items (Rosenberg and Cooper 1990). These biases, however, are common to all methods involving the analysis of stomach contents.

ACKNOWLEDGMENTS

We thank K. K. Aulwes and J. Grady for assisting wit^. "Jie laboratory work. J. R.

Gionfriddo provided veterinary advice. We also thank E. E. Klaas for reviewing an earlier draft of

the manuscript and offering helpful suggestions. Funding was provided by Miles, Inc., Rhdne- Poulenc, American Cyanamid, and Dow Elanco. This is Journal Paper J-15746 of the Iowa

Agriculture and Home Economics Experiment Station, Ames; Project 2168.

LITEEiATURE CITED

Brensing, V. D. 1977. Nahrungsokologische Untersuchungen an Zugvogeln in einem sQdwestdeutschenDurchzugsgebietWahrend des Wegzugs. Vogelwarte 29:44-56. [Cited in Ford et al. (1982)]

Ford, H. A., N. Forde, and S. Harrington. 1982. Non-destructive methods to determine the diets

of birds. Corella 6:6-10.

Gales, R. P. 1987. Validation of the stomach-flushing technique for obtaining stomach contents of

Penguins. Ibis 129:335-343.

Home, R. S. C. 1985. Diet of Royal and Rockhopper Penguins at Macquarie Island. Emu 85:150-

156. 10

Laursen, K. 1978. Interspecific relationships between some insectivorous passerine species,

illustrated by their diet during spring migration. Omis Scand. 9:178-192.

Moody, D. T. 1970. A method for obtaining food samples from insectivorous birds. Auk 87:579.

Randall, R. M., and 1. S. Davidson. 1981. Device for obtaining food samples from the stomachs of

Jackass Penguins. S. Afr. J, Wildl. Res. 11:121-125.

Rosenberg, K. V., and R. J. Cooper. 1990. Approaches to avian diet analysis. Stud. Avian Biol.

13:80-90.

Ryan, P. G., and S. Jackson. 1986. Stomach pumping: is killing seabirds necessary? Auk 103:427-

428.

Wilson, R. P. 1984. An improved stomach pump for penguins and other seabirds. J. Field

Omithol. 55:109-112.

Wilson, R. P., M.-P. Wilson, D. C. Duffy, B. A, M, and N. Klages. 1989. Diving behaviour and

prey of the Humboldt Penguin (Spheniscus humboldti^. J. Omithol. 130:75-79.

Zach, R,, and J. B. Falls. 1976. Bias and mortality in the use of tartar emetic to determine the diet

of Ovenbirds (Aves: Parulidae). Can. J. Zool. 54:1599-1603. 11

CHAPTER in. GRTT USE BY HOUSE SPARROWS: EFFECTS OF DIET AND GRTT SIZE

A paper accepted for publication in The Condor

James P. Gionfriddo and Louis B. Best

ABSTRACT. Free-ranging House Sparrows (Passer domesticus'> were captured with mist nets in central Iowa from August through March, 1990-1993, and their gizzard contents were used to compare grit use by sex, season, and diet. Males and females did not differ in mean grit amounts or sizes (overall mean size = 0.5 mm) in their gizzards. Gizzards of birds captured during

March and August contained more grit than those of birds captured during September through

February (3? = 674 vs. 477). Gizzards containing > 75% animal material (insects) had more grit than those containing > 75% plant food (x = 681 vs. 531). Aviary experiments then were conducted with captive House Sparrows to evaluate the effects of diet and grit size on grit choice and retention.

When birds were given grit particles 0.2 -1.4 mm in size and either soft animal food (canned dog food) or hard plant food (wild bird seed), grit in gizzards of birds on the two diets did not differ in mean number or size. When birds were given both animal and plant food and either small (0.2 -

0.4 mm) or large (1.0 -1.4 mm) grit, gizzards of birds consuming small grit contained 5 times more particles than those of birds consuming large grit (5? = 275 vs. 51). In experiments evaluating grit retention, most grit in gizzards was replaced within 5 days. Grit replacement rates were unaffected by diet, but birds given only hard, plant food averaged more grit per gizzard than those given only soft, animal food (X = 538 vs. 205). Gizzards of House Sparrows given only small grit consistently retained grit longer and contained more particles (5? = 853 vs. 174) than those of birds given only large grit. 12

INTRODUCTION

Despite a long history of interest in the avian gizzard and its function (e.g., Borelli 1743,

Rgaumur 1756, Spallanzani 1783 [all cited in Famer I960]), relatively little is known about the process and dynamics of grit use by birds. Grit use is widespread among birds (Meinertzhagen

1954,1964; Best and Gionfriddo 1991), and the value of grit in increasing avian digestive efficiency has been demonstrated (Fritz 1937, Lienhart 1953, Titus 1955, Smith 1960). Grit also is known to provide supplementary calcium and other minerals which may be critically important to granivores and other species with low-calcium foods (McCann 1961, Harper 1%3, Harper and Labisky 1964,

Korschgen 1964, Norns et al. 1975). Little information is available, however, regarding the factors that influence grit use.

The amount of grit used by birds may be influenced by grit size and bird diet. Within a species, an inverse relationship sometimes exists between mean grit size and the number of grit particles in the gizzard (Alonso 1985, Best and Gionfriddo 1991), indicating that birds consuming smaller grit generally use more particles. Because birds use grit to improve mechanical grinding of food in the gizzard, the value of (and need for) grit should vary with diet. Several authors have noted greater grit use when diets consist of hard, coarse foods such as seeds and other plant material (Porkert 1972, Norris et al. 1975, Bishton 1986, Hogstad 1988). Some avian digestive systems are adapted to enable birds to exploit different amounts and t)rpes of foods seasonally. For

example, some species regulate digestive efficiency by seasonal changes in gut length (Dykstra and

Karasov 1992) or by pvocessing different foods at different rates (e.g., Levey and Karasov 1989,

1992). Adaptive, seasonal variation in grit use might be expected to accompany seasonal shifts in

the diets of some avian species. 13

The amounts and characteristics of grit in bird gizzards depend, not only on selection of grit particles by the birds, but also on retention of at least some of those particles in the gizzard.

Retention of individual grit particles is influenced by the rate at which grit is ingested (McCann

1939, Smith and Maclntyre 1959, Tagami 1974, Trost 1981). When birds have free access to grit, they may consume and eliminate considerable amounts daily (Lienhart 1953; May and Braun 1973;

Alonso 1985; Gionfriddo, pers. obs.). On the other hand, birds suddenly deprived of grit can reduce their output of grit and retain particles in their gizzards for long periods (Smith and Rastall

1911, Kraupp 1924, McCann 1939, Walter and Aitken 1961). Other factors, including grit size and diet, also may influence grit retention in the gizzard. Some particles may be retained longer than others because of their size (Smith 1960, Roland et al. 1972, Tagami 1974). Diet can affect retention in several ways. For example, coarse, hard diets may increase the grit ingestion rate and thereby reduce retention (Trost 1981). Hard diets also may reduce grit retention by accelerating grit particle disintegration and elimination (Norris et al. 1975).

In addition to their importance in avian digestion, the dynamics of avian grit use also have direct implications for avian exposure to pesticides. Each year, granular pesticides are applied to millions of hectares of com and other crops in North America to control agricultural pests (U.S.

Dep. Agric. 1992). The toxicity of these materials to birds (Balcomb et al. 1984, Hill and Camardese

1984) has generated interest in evaluating avian risk associated with pesticide use. One factor influencing risk ii

understanding of the dynamics of grit use by birds is therefore important in assessing avian risk associated with granular pesticide use. 14

To gain a better understanding of the influence of diet and grit size on avian grit use, we examined grit use by House Sparrows (Passer domesticus>. First, we characterized natural grit use by free-ranging birds and compared grit use by sex, season, and diet. We then conducted a series of aviary experiments designed to evaluate the influence of diet and grit size on grit choice and retention. The House Sparrow was chosen because it uses a substantial amount of grit (Keil 1973,

Pinowska 1975, Best and Gionfriddo 1991) and has a seasonally varying diet. House Sparrows rely heavily on seeds year-round but also consume insects when available (Kalmbach 1940, Gavett and

Wakeley 1986). In addition, as ground-foraging granivores (De Graaf et al. 1985), House Sparrows represent the avian feeding guild most likely to be exposed to granular pesticides.

METHODS

GRIT USE BY FREE-RANGING HOUSE SPARROWS

Free-ranging House Sparrows were captured with mist nets from August through March,

1990-1993, at rural sites in Story and Boone counties in central Iowa. Birds were euthanized and taken to the laboratory for analysis of gizzard contents. Each gizzard was sliced in half with a razor blade, and the contents were flushed into a petri dish where they were examined and sorted under a zoom, stereomicroscope. Diet was characterized by visually estimating the percentages (by volume, to the nearest 5 %) of plant and animal material. Our estimates of the percentage of animal material may be lower than the amounts actually consumed, because some animal foods pass through the gizzard much more quickly than many plant foods. Grit particles were separated from other gizzard contents and counted. Particles < 0.1 mm in size were excluded because they were considered soil material and not grit selected by the birds.

Grit particles in about one-fourth of the House Sparrow gizzards were characterized individually. Gizzards were chosen for this evaluation to include roughly equal numbers of males 15 and females from each season (see below) and from each of 6 capture locations. The longest and shortest dimensions of each grit particle were measured to the nearest 0.1 mm with an ocular micrometer in the microscope. For each particle, these two values were averaged for an overall measure of grit size. A grit shape index value was calculated for each grit particle by dividing the longest by the shortest dimension. These values were > 1.0, with 1.0 representing a somewhat spherical shape and larger values representing oval to oblong shapes. Grit surface texture was classified into five categories by using a scheme developed by petrologists to describe mineral grains (El-Hinnawi 1966:15), The 5 surface-texture categories were angular, sub-angular, sub-rounded, rounded, and well-rounded (see Best and Gionfriddo 1991, Fig. 1). An overaU mean surface-texture value, the surface-texture index, was calculated for each bird by giving grit particles in the angular category a value of 1, those in the sub-angular category a value of 2, etc.

We tested for seasonal effects on grit use by comparing gizzard contents of birds captured at 6 rural sites during March and August with those of birds captured at the same locations during

September-February. Relatively heavy use of insects by Iowa House Sparrows begins in March and ends in August (Kalmbach 1940; Gionfriddo and Best, unpubl. data). Therefore, although birds were not collected during much of the annual peak in insect activity (April-July), gizzard contents of birds captured in March and August should reflect seasonal patterns of grit-use in response to a diet containing an increased amount of insects. For convenience, we will refer to the

March/August collection period as the "insect season" and September-February as the "no insect season." Food in gizzards of most (241 of 245) free-ranging House Sparrows consisted of either >

75% plant or > 75% animal material, so we examined the influence of diet on grit use by comparing grit from birds that had > 75% plant food in their gizzards with grit from those having > 75% animal food. Analysis of variance was used to test if interactions among sex, season, and diet affected 16 gizzard grit counts. Two-tailed t-tests were used to determine if mean grit counts, sizes, shape index values, or surface-texture values differed (P < 0.05) by sex, season, or diet.

EXPERIMENTS

Additional free-ranging House Sparrows were captured throughout the year, fitted with numbered aluminum leg bands, and put in outdoor aviaries where they were held for at least 3 days (Grit Size and Diet Experiments) or 7 days (Grit Retention Experiments) to acclimate to captivity before experiments were begun. During acclimation, birds were provided with the same type of food they later received during experiments.

Before starting each experiment, we anesthetized each bird, inserted a ball-tipped intubation needle into the gizzard, and used a syringe to flush the gizzard with a saline solution.

This technique effectively removes all or nearly all food and grit from the gizzards of most House

Sparrows (Gionfriddo et al., in press). After recovery from anesthesia, birds were returned to the aviaries and given food, water, and grit. The food and grit provided varied, depending upon the experiment (see below).

Birds assigned (randomly) to a given experimental treatment were housed together in an aviary compartment measuring 3.7 x 4.6 x 2.1 m. The plant diet was a commercially prepared seed mixture (Cardinal Brand Wild Bird Feed, Des Moines Feed Co., Des Moines, LA) containing millet, milo, cracked com, sunflower seeds, peanuts, and wheat. The animal diet was canned dog food

(Grit Size and Diet Experiments: Ken-L-Ration Beef Dinner Dog and Puppy Food, Quaker Oats

Co., Chicago, IL; Grit Retention Experiments: Prescription Diet i/d. Hill's Pet Products, Topeka,

KS). In each aviary compartment, grit was presented to the birds in two trays, each consisting of a

square lumber frame affixed to the concrete aviary floor. The surface (bottom) of each grit tray

measured 0.5 m^, except in the Diet Experiment, in which a relatively large volume of grit 17 necessitated the use of l.O-m^ trays. In the Grit Retention Experiments the bottoms of the grit trays consisted of the concrete aviary floor, but in the Grit Size and Diet Experiments, Masonite® was attached to the wooden frames and used as the grit tray bottoms. After each experiment.

House Sparrows were euthanized, and gizzards were removed and preserved in 95% ethanol.

Grit Size and Diet Experiments

In the Grit Size Experiment, we gave birds either small or large grit. In one treatment, grit trays contained grit sieved to a size range of 0.2 - 0.4 mm (representing the lower end of the normal range of grit sizes used by free-ranging House Sparrows [Best and Gionfriddo 1991]). In the other treatment, trays contained grit ranging from 1.0-1.4 mm (upper end of the normal grit size range). Each grit tray was supplied with 25 cc of grit. All birds had access to both hard plant food and soft animal food.

In the Diet Experiment, we gave birds access to either hard plant food or soft animal food.

Both groups of birds were supplied with grit representing nearly the entire range of grit sizes

normally used by free-ranging House Sparrows (0.2 - 1.4 mm). To ensure that an ad libitum

supply of particles of various sizes within that overall range was available to birds, we placed 150

cc of grit in each grit tray.

In both experiments, which were conducted in June, 25 House Sparrows were randomly

assigned to each treatment. Grit, which consisted of sand obtained from a sand pit near Ames,

Iowa, was replaced in the trays every 2 days. Both experiments ended after 14 days. Later,

gizzard contents were examined, and grit particles were counted and measured (longest and

shortest dimensions). Two-tailed t-tests with a significance level of P < 0.05 were used to compare

mean grit counts in gizzards of birds in the paired treatments. 18

Grit Retention Experiments

The Grit Retention Experiments were designed to determine how long individual grit particles are retained in the gizzard and if retention is influenced by diet or grit size. The procedure consisted of giving House Sparrows access to Colorado quartz grit for at least 2 weeks and then shifting the birds to microcline feldspar grit. (In one experiment the shift was from feldspar to quartz.) Particles of the two mineral types were extremely similar in size, shape, surface texture, color, hardness, and specific gravity. The rates of replacement in gizzards of the first grit t5rpe by the second then were determined by euthanizing birds at regular intervals after the shift and examining their gizzard contents.

A preliminary experiment was conducted to determine an appropriate schedule for euthanizing birds after the grit type was changed. The results suggested that replacement (in gizzards) of the first grit t3rpe by the second was a slow, gradual process that might take many weeks to complete. Accordingly, in subsequent experiments, we euthanized birds 5,10,15, 20, 25, and 30 days after the substitution (in grit trays) of the second grit type for the first. Our main experimental results demonstrated repeatedly (see below) that most grit was replaced in gizzards within 5 days, and thus, a final experiment (Short Intervals Retention Experiment) was conducted in which birds were euthanized H, 1/ 2, 4, and 8 days after the grit type was changed.

A critical assumption underljring these experiments was that House Sparrows could not distinguish between quartz and feldspar particles and responded in the same way to the two grit

types. It also was assumed that birds' gizzards would respond to the two grit types in the same

way and not retain one type longer than the other. We tested these assumptions experimentally.

We gave 18 House Sparrows access for 14 days to a mixture of equal volumes of quartz and

feldspar particles. Chi-square analysis of the contents of individual gizzards revealed that in 13 of 19 the gizzards the number of particles of the two grit types did not differ significantly (P > 0.05).

Four of the remaining five gizzards contained more quartz grit, and one contained more feldspar.

In the Quartz-to-Feldsparand the Feldspar-to-Quartz Retention Experiments, we tested if birds would show the same pattern of grit replacement in gizzards when quartz was shifted to feldspar as when feldspar was shifted to quartz. The similarity in the results of these two experiments (see below) also supported the assumption that House Sparrows were unable to distinguish between quartz and feldspar particles. Although it is possible that the birds could detect differences between quartz and feldspar particles but showed no preference for either, we think this unlikely, given the difficulty we often had distinguishing between the two grit types under a stereomicroscopewith optimal lighting (see below).

Before the experiments, which were conducted during November-January, the grit was hammermilled and then tumbled in a vibrating tumbler for 5 days to dull any sharp, jagged edges.

It then was sieved and sorted into 0.2-mm size classes. In all experiments except the Gnt Size

Retention Experiment, we used equal volumes of grit in the 0.2 - 0.4, >0.4 - 0.6, >0.6 - 0.8, >0.8 -1.0,

>1.0 - 1.2, and >1.2 - 1.4 mm size classes. In the Grit Size Retention Experiment, one group of birds was given only small (0.2 - 0.4 mm) grit, and another group was given only large (1.0 - 1.4 mm) grit. In all experiments, each grit tray initially contained 25 cc of grit, to which 2 cc of grit were added daily to ensure a continuous ad libitum supply.

In the laboratory, all quartz and feldspar particles in each gizzard were identified and counted. Because the quartz and feldspar particles were so similar in appearance, they could be distinguished only by using a microscope. Feldspar particles had flat cleavage planes on portions of their surfaces, whereas the surfaces of quartz particles were irregular throughout. The 20 appearance of the particles when viewed through a polarized light filter also aided in distinguishing the two grit types.

RESULTS grtt use by free-ranging house sparrows

AD but 1 of the 245 gizzards of free-ranging House Sparrows contained grit. Grit counts in individual gizzards varied greatly, ranging from 0 to 3,204, writh a mean of 580.3 (+ 489.6 [SD]) and a median of 462. There were no 2-way or 3-way interactions among sex, season, and diet that affected grit counts (P > 0.159). (The unexpected absence of an interaction between season and diet resulted from House Sparrows' consuming seeds and insects during both seasons.) Males and females did not differ in their mean grit counts overall (t = 0.33, 243 df, P = 0.743) or during either season (insect: t = 0.37, 127 df, P = 0.710; no insect: t = 0.38,114 df, P = 0.704). Gizzards of House

Sparrows captured during the insect season contained more grit particles than those of birds captured in September-February (insect = 673.6 + 553.7, N = 129; no insect = 476.6 + 382.9, M =

116; t = 3.20, 243 df, P = 0.002). Gizzards containing > 75% animal food had more grit than those containing > 75% plant material (animal = 681.2 + 541.9, M = 85; plant = 530.9 + 455.7, M = 156; t =

2.29, 239 df, P = 0.023).

Grit particles in the 60 House Sparrow gizzards in which individual particles were analyzed ranged in size from 0.1 mm to 2.4 mm, with a mean of 0.5 mm (+ 0.1 [SD]). The most common grit size class was 0.3 - 0.4 mm (24% of all grit particles), and more than two-thirds of the grit in the 60 gizzards was between 0.2 and 0.5 mm. Mean grit size did not differ between the sexes (t = 0.60, 58 df, P = 0.548) or seasons (t = 0.84, 58 df, P = 0.407). Only 8 of the 60 gizzards for which individual grit particles were measured contained > 75% animal food material. Therefore, meaningful comparisons between diets could not be made for grit size, shape, and surface texture. 21

Shape index values of grit particles in the 60 House Sparrow gizzards ranged from 1.0

(approximately spherical) to 7.2 (oblong), with a mean value of 2.0 + 0.2. The distribution of grit particle shapes was highly skewed toward more spherical shapes; most (79%) particles had shape index values of less than 2.0. Mean grit shape index values did not differ between the sexes (t =

0.67,58 df, P = 0.505). Grit in gizzards of House Sparrows captured during the insect season had lower mean shape index values than grit in birds captured at other times of year (insect = 1.9 +

0.1, N = 29; no insect = 2.0 + 0.2, N = 31; t = 2.16, 58 df, P = 0.035), although this difference was probably not biologically meaningful.

House Sparrow grit tended to be of intermediate surface textures, with more than half

(54%) of all particles sampled being sub-rounded, and less than 5% being angular or well-rounded.

Mean grit surface-texture values (3.0 + 0.2 overall) did not differ between the sexes (t = 1.10,58 df,

P = 0.276) or between seasons (t = 0.91,58 df, P = 0.368). grit size experiment

Birds consuming small grit had more particles in their gizzards than birds consuming large grit (t = 3.46,48 df, P = 0.001). The mean grit count among birds using small grit was more than five times that of birds using large grit (275.1 + 322.3 vs. 51.4 + 26.4; ranges: 10 - 1,191 vs. 16 - 114).

Responses of males and females were simUar (small grit: t = 0.50,23 df, P = 0.621; large grit: t =

1.07, 23 df, P = 0.297).

The large differences in numbers of particles of the two grit sizes found in gizzards suggested that the birds consuming small grit had used more particles to satisfy a need for a specific volume of grit in the gizzard. We examined this by estimating mean grit volumes for birds in the two grit-size treatments. By counting the particles in 40 cc of large and 1 cc of small grit, we found that it took about 45 times as many small particles as large ones to occupy the same volume 22 of space (1 cc). A mean volume per particle (including inter-particle spaces) was calculated for each grit size, and from these values we determined that birds consuming large grit had a mean grit volume more than 8 times that of birds using small grit (0.09 + 0.05 vs. 0.01 + 0.01 cc). diet experiment

Overall, mean numbers of grit particles in the gizzards of birds on the two diets did not differ (plant = 130.3 + 206.2 [range 18-1,120]; animal = 112.8 + 68.0 [11-322]; t = 0.39, 48 df, P =

0.696). Among females, however, gizzards of birds on the animal diet contained more grit particles than those of birds on the plant diet (animal = 143.0 + 78.7; plant = 78.5 + 46.3; t = 2.55, 24 df, P =

0.018).

Grit in gizzards of birds on the two diets did not differ in mean size (both = 0.8 mm + 0.1; t = 0,60,48 df, P = 0.552). There was no evident relationship between mean grit size and number of grit particles in gizzards of House Sparrows maintained on either diet (plant: N = 25, r = 0.497; animal; N = 25, r = 0.214). grit retention experiments

The results of the Quartz-to-Feldspar and Feldspar-to-Quartz Retention Experiments were very similar (Fig. la). In both experiments, replacement in gizzards of the initial grit type by the second type was very rapid during the first 5 days, followed by much more gradual replacement

until the end of the experiment at 30 days. Mean numbers of grit particles per gizzard in these

two experiments did not differ (Quartz-to-Feldspar: 257.3 + 139.2, Feldspar-to-Quartz:197.5 ± 137.5;

t = 1.67, 58 df, P = 0.100).

In the Diet Retention Experiment, the temporal patterns of grit replacement in gizzards of

birds were similar to those in the Quartz-to-Feldspar and Feldspar-to-Quartz Retention Experiments

(Fig. lb). Grit turnover did not differ between birds fed plant food and those fed animal material. 23

Birds in the two groups differed, however, in the mean number of grit particles per gizzard (plant diet: 538.4 ± 330.6, animal diet: 205.1 ± 110.3; t = 5.16,57 df, P < 0.001).

In the Grit Size Retention Experiment, House Sparrows given only small grit consistency retained grit longer than those given only large grit (Fig. Ic). In both grit size treatments, as in the other retention experiments, most of the grit in gizzards was replaced within 5 days. Gizzards of birds consuming small grit, however, contained comparatively large proportions (5? = 35%) of quartz grit 5 days after the birds had been switched to feldspar grit (Fig. Ic). Corresponding mean values for birds in other retention experiments never exceeded 25% (Fig. la,b). In the Grit Size

Retention Experiment, birds given small grit averaged nearly five times more grit particles per gizzard than those given large grit (853.0 + 736.9 vs. 173.5 + 90.7; t = 5.01,58 df, P < 0.001). Seven of the 30 House Sparrows given small grit had more than 1,500 particles per gizzard, whereas the greatest number of large particles found in a single gizzard was 415. These results indicate that, when birds use small grit, their gizzards retain individual grit particles longer and contain more particles than when relatively large grit is consumed.

The Short Intervals Retention Experiment characterized grit retention and replacement during the critical first few days after substitution of feldspar for quartz. The results suggest that

grit consumption, at least under the conditions of this experiment, is a daily activity (Fig. Id).

Moreover, much of the grit consumed by birds may be retained for only a few hours. Nearly 40%

of the grit found in gizzards of experimental birds euthanized only 6 hours after the shift to

feldspar grit was feldspar. Among birds euthanized 24 hours after grit substitution, a mean of

only 12% of the grit in gizzards was quartz. The quartz proportion remained fairly stable

throughout the remaining 7 days of the experiment. 24

DISCUSSION

Free-ranging House Sparrows in central Iowa use large amounts of grit throughout the year. This finding is consistent with the results of German research, which showed that year- round, by weight. House Sparrow gizzards contained 66% grit and 34% food (Pfeifer and Keil

1962, cited in Keil 1973). Analysis of additional German House Sparrow gizzards collected in winter pelded similar results (65% grit and 35% food) (Keil 1973). In Poland, only 1 of 1,337 female House Sparrow gizzards collected during the breeding season lacked grit, and grit weight consistently exceeded food weight (Pinowska 1975).

Free-ranging House Sparrow males and females did not differ in the numbers of grit particles in their gizzards nor in the mean values for grit size, shape, and surface texture.

Differences in grit use between the sexes are not always evident (Siegfried 1973; Alonso 1985;

Norman and Brown 1985; Gionfriddo and Best, unpubl. data). When present, such differences may be related to inneased calcium requirements of females during egg laying. Reproductive female birds are able to adjust their consumption of calcareous grit to meet the caldum demands of egg laying (Sadler 1961, Harper 1964, Taylor 1970). Pinowska and Krasnidd (1985) found that female House Sparrows increased their grit use for about 2 days during egg laying to meet elevated calcium and magnesium requirements. Our study was not designed to detect grit-use shifts of such short duration.

Characteristics of grit used by free-ranging Iowa House Sparrows differed slightly from

those reported for a sample of 77 midwestem House Sparrows (Best and Gionfriddo 1991). Grit in

gizzards in the present study was smaller (mean size = 0.5 vs. 0.7 mm), more oblong (mean shape

= 2.0 vs. 1.7), and less angular (mean surface texture = 3.0 vs. 2.8). Moreover, the median grit

count per gizzard was 6 times greater than in the midwestem birds (462 vs. 69). These differences. 25 however, may simply reflect the substantial variation in grit use observed among House Sparrows captured at different locations (Gionfriddo and Best, unpubl. data). Such variation probably is influenced by geographical differences in the availability of various types of grit. The differences in median grit counts between the two House Sparrow samples probably are related to the differences in mean grit size. Human error and subjectivity in making the measurements also could have contributed to the differences between the studies.

Grit size seems to be a major factor influencing grit use. Birds consuming small grit are likely to use more grit particles than those consuming larger grit. In both the Grit Size Experiment and the Grit Size Retention Experiment, gizzards of House Sparrows consuming small grit contained about 5 times as many particles as those of birds consuming large grit. These results are consistent with the pattern that we observed in free-ranging House Sparrows (see above) and with the findings of other researchers. Smith (1960) reported that voluntary grit consumption by domestic chicks fGallus domesticus) declined significantly with increasing grit size. Several field studies also have determined that, in general, the larger the size of the grit particles, the fewer are ingested and retained in the gizzard (Myrbergetet al. 1975, Norris et al. 1975, Alonso 1985). Free- ranging birds typically have access to and use a wide range of grit particle sizes (Best and

Gionfriddo 1991).

Avian grit use also is influenced by diet. The ultimate (functional) cause of many grit-use

shifts probably is seasonal dietary changes that produce variation in the value of grit. Field studies

have documented seasonal diet and grit-use changes in several avian species. Hogstad (1988)

reported that grit use by Bramblings fFringilla montifringilla^ was much greater when they

consumed seeds than when they shifted to soft insect larvae. As Dunnocks (Prunella modularis't

changed their diet in late summer from insects to seeds and insects, their grit use increased 26 significantly (Bishton 1986). A similar association between inaeased grit use and greater consumption of hard (usually plant) foods also has been documented in other research

(Meinertzhagen 1954, Porkert 1972, Norris et al. 1975) and in our Diet Retention Experiment.

In House Sparrows, the efficient digestion of hard-bodied coleopterans (which constitute more than half the animal matter consumed [Kalmbach 1940, Gavett and Wakeley 1986]) may require an increase in grit use. Pinowska (1975) reported that grit weight increased and decreased with the frequency of insects in gizz&rds of female House Sparrows during the breeding season and concluded that grit may assist in the digestion of chitinous insect parts. Free-ranging birds in

Iowa (present study) used more grit when they fed heavily on insects (> 75% of the food in the gizzard) than when they consumed primarily seeds. Their gizzards also contained more grit during the months when insects were consumed relatively heavily (March and August) than during the months when they were not (September-February).

The identity of the proximate cue (e.g., dietary or photoperiod change) that triggers seasonal changes in avian grit use remains uncertain. Some evidence suggests that such grit-use

shifts may be elicited by changes in diet. Experiments with captive Willow Ptarmigan (Lagopus lapopus^ showed that birds consuming coarse food (twigs and buds of willow fSalixl and birch

[Betula]) ingested and excreted 2-4 times as much grit as birds fed pelleted food, and that

ptarmigan kept on a constant diet maintained a constant grit intake throughout the year (Norris et

al. 1975). Other evidence, however, is equivocal. For example, two of our experiments with

captive House Sparrows simultaneously compared grit use by birds on two diets (hard plant and

soft animal). In the Diet Retention Experiment, gizzards of birds consuming plant food had more

than twice as much grit as those of birds fed Hill's dog food. In the Diet Experiment, however,

although more grit was found in gizzards of birds fed plant food than in those of birds fed Ken-L- 27

Ration dog food, the difference was not significant statistically. Why the birds consuming Ken-L-

Ration in the Diet Experiment used about as much grit as birds fed seeds is uncertain, but may be related to the amount of roughage in the dog food. Ken-L-Ration contains 3 times more crude fiber than Hill's dog food (according to labels). The latter is specially formulated for high digestibility and thus better represents a "soft animal food."

Although we found no evidence of seasonal changes in House Sparrow grit size, such changes have been documented in other avian species with seasonal diet shifts. May and Braun

(1973) found that White-tailed Ptarmigan fLagopus leucurus) used proportionately more large grit during seasons when hard, difficult-to-digestfood items (willow buds, twigs, and leaves) were consumed. Alonso (1985) reported that Spanish Sparrows (Passer hispaniolensis^ consumed larger grit particles when they fed on large insects and cereal grains (spring and summer) than when they fed mainly on seeds (faU and winter). He concluded that food item size (rather than hardness) determined the size of grit particles used. Because grit facilitates the mechanical breakdown of food in the gizzard, it is likely that grit use by many avian species is influenced by the sizes and types of food consumed.

The retention of individual grit particles in birds' gizzards is highly variable. Under certain conditions, such as when birds are denied access to grit, retention may be very long, even > 1 year

(Kraupp 1924, Walter and Aitken 1%1, Robel and Bisset 1979). On the other hand, when birds have daily access to abundant grit sources, they may continually replenish grit in their gizzards

(Lienhart 1953, May and Braun 1973, Alonso 1985). In the latter instance, many grit particles may be retained only briefly in the gizzard, passing completely through the digestive tract in a few hours. Why other particles are retained in the gizzard for relatively long periods is unknown, but grit characteristics such as size, shape, and surface texture may play a role. Of the variables 28 examined in our research, grit particle size seemed to exert the most influence on retention. In

general, smaller grit particles were retained longer than larger particles when birds were given

either small or large grit. This result, however, differs from the findings of other laboratory studies

in which groups of domestic chicks were fed (ad libitum) grit of different sizes (one size per

group). Smith (1960) found that grit retention on a percentage ingested basis increased with

increasing grit size. Tagami (1974), on the other hand, reported that chicks retained more medium-

sized (1.2 - 2.4 mm) than large (2.4 - 3.4 mm) particles, and very few small (0.6 -1.2 mm) particles.

Gizzards of free-ranging birds, however, usually contain grit particles of many different sizes (Best

and Gionfriddo 1991), and in nature, retention processes act on grit particles representing a much

wider range of sizes than those in gizzards of these experimental birds.

The results of our research have implications relative to avian exposure to granular

pesticides because one potential route of exposure involves birds' mistakenly consuming granules

as a source of grit (Best and Fischer 1992). Granular pesticides are applied during the spring and

summer, when free-ranging birds generally have access to abundant sources of grit. Under such

conditions, lengthy retention of grit in gizzards is not necessary because the grit in gizzards can be

replenished daily. As a result, birds may face a greater risk of exposure to pesticide granules by

consuming grit often. Furthermore, at least in some avian species, grit use increases during this

time of year. Documenting seasonal and other patterns in grit use by birds, as we have done with

House Sparrows, will improve our knowledge of the relative vulnerabilities of various groups of

birds to granular pesticide use. If ingestion of pesticide granules is an important route of avian

exposure, then an understanding of the grit-use preferences (grit size, shape, surface texture, etc.)

and patterns (seasonal, sexual, dietary, etc.) of other species may be useful in designing pesticide

granules to make them less attractive to birds. 29

House Sparrow behavior in the artificial conditions of the aviary may not accurately represent the behavior of free-ranging birds in a natural environment. Grit consumption rates of captive birds may have been abnormally high or low. For example, captivity-induced "boredom" may have led to abnormally high grit consumption rates. If that occurred, then the high turnover rates (short retention) of grit in gizzards of the captive birds could simply have resulted from artificially accelerated grit consumption. High grit turnover rates, however, also were found in free-ranging House Sparrows (Fischer and Best, unpubl. data). Also, the fact that the mean grit counts in gizzards of free-ranging House Sparrows in the present study were greater than those of experimental birds suggests that the grit consumption rates of the captive birds were not abnormally high. The relatively low grit counts in the experimental birds may have been related to the birds' responses to the surfaces (bottoms) of the grit trays. In the Diet and Grit Size

Experiments, the slippery texture of the Masonite® used as grit tray bottoms may have made birds uncomfortable, reducing the time they spent in the grit trays. Mean grit counts per gizzard were greater when the conaete aviary floor was used as grit tray bottoms (in the Grit Retention

Experiments), and greater still when a crusted soil surface was used (Gionfriddo and Best, unpubl. data). Although our study has limitations, it represents one of the first experimental attempts to quantify the influences of grit size and bird diet on grit use and on the retention and replacement of grit in the gizzard. As such, it constitutes an important first step in understanding the dynamics of grit use and retention in birds.

ACKNOWLEDGMENTS

We are grateful to K. L. Andersen, J. D. Best, N. Best, J. K. Creswell, B. J. Giesler, J. R.

Gionfriddo, D. S. Huntrods, L. D. Igl, A. L, Linville, B. C. Schoeberl, and M. K. Trzdnski for assisting with laboratory work. K. L. Andersen and J. R. Gionfriddo also assisted with data 30 tabulation. B. J. Giesler captured and maintained birds and assisted with all experiments. J. J.

Dinsmore, E. E. Klaas, and an anonymous reviewer read earlier drafts of the manuscript and offered many helpful suggestions. Funding was provided by Miles, Inc., Rhone-Poulenc, American Cyanamid, and Dow Elanco. This is Journal Paper J-15832 of the Iowa Agriculture and

Home Economics Experiment Station, Ames, Project 2168.

LITERATURE CITED

ALONSO, J. C. 1985. Grit in the gizzard of Spanish Sparrows (Passer hispaniolensist. Vogelwarte

33:135-143.

Balcomb, R., R. Stevens, and C. Bowen n. 1984. Toxicity of 16 granular insecticides to wild-

caught songbirds. Bull. Environ. Contam. Toxicol. 33:302-307.

Best, L. B., and D. L. Fischer. 1992. Granular insecticides and birds: factors to be considered in

understanding exposure and reducing risk. Environ. Toxicol. Chem. 11:1495-1508.

Best, L. B., and J. P. Gionfriddo. 1991. Characterizationof grit use by cornfield birds. Wilson

BuU. 103:68-82.

BISHTON, G. 1986. The diet and foraging behaviour of the Dunnock Prunella modularis in a

hedgerow habitat. Ibis 128:526-539.

BORELLI, G. A. 1743. De motu animalium. P. Gosse, The Hague.

De Graaf, R. M., N. G. Tilghman, and S. H. Anderson. 1985. Foraging guilds of North

American birds. Environ. Manage. 9:493-536.

Dykstra, C. R., and W. H. Karasov. 1992. Changes in gut structure and function of House

Wrens /Troglodytes aedon) in response to increased energy demands. Physiol. Zool.

65:422-442. 31

El-Hinnawi, E. E. 1966. Methods in chemical and mineral microscopy. Elsevier, New York. 222

PP-

Farmer, D. S. 1960. Digestion and the digestive system, p. 411-467. In A. J. Marshall [ed.].

Biology and comparative physiology of birds. Vol.1. Academic Press, New York.

Fritz, J. C. 1937. The effect of feeding grit on digestibilityin the domestic fowl. Poult. Sd. 16:75-

79.

Gavett, A. P., and J. S. Wakeley. 1986. Diets of House Sparrows in urban and rural habitats.

Wilson Bull. 98:137-144.

Gionfriddo, J. P., L. B. Best, and B. J. Giesler. In press. A saline flushing technique for

determining the diet of seed-eating birds. Auk.

Harper, J. A. 1963. Calcium in grit consumed by juvenile pheasants in east-central Illinois. J.

Wildl. Manage. 27:362-367.

Harper, J. A. 1964. Caldum in grit consumed by hen pheasants in east-central Illinois. J. Wildl.

Manage. 28:264-270.

Harper, J. A., and R. F. Labisky. 1964. The influence of caldum on the distribution of pheasants

in Illinois. J. Wildl. Manage. 28:722-731.

Hill, E. P., and M. B. Camardese. 1984. Toxidty of anticholinesteraseinsectiddes to birds:

technical gtads versus granular formulations. Ecotoxicol. Environ. Saf. 8:551-563.

HOGSTAD, O. 1988. Foraging pattern and prey selection of breeding Bramblings Fringilla

montifringilla. Fauna Norv. Ser. C, Cindus 11:27-39.

Kalmbach, E. R. 1940. Economic status of the English Sparrow in the United States. U.S. Dep.

Agric. Tech. Bull. 711. 32

Keil, W. 1973. Investigations on food of House- and Tree Sparrows in a cereal-growing area

during winter, p. 253-262. In S. C. Kendeigh and J. Pinowski [eds.]. Productivity,

population dynamics and systematicsof granivorous birds. PWN - Pol. Sd. Publ.,

Warszawa.

Korschgen, L. J. 1964. Foods and nutrition of Missouri and midwestem pheasants. Trans. N.

Am. Wildl. Nat. Resour. Conf. 29:159-180.

Kraupp, B. F. 1924. The digestive organs of the fowl. Vet. Med. 19:522-523.

Levey, D. J., and W. H. Karasov. 1989. Digestive responses of temperate birds switched to fruit

or insect diets. Auk 106:675-686.

Levey, D. J., and W. H. Karasov. 1992. Digestive modulation in a seasonal frugivore, the

American Robin fTurdus migratorius^. Am. J. Physiol. 262:G711-G718.

LLENHART, R. 1953. Recherches sur le role des cailloux contenus dans le gSsier des oiseaux

granivores. Bull. Soc. Sd. Nancy 12:5-9.

May, T. a., AND C. E. BRAUN. 1973. Gizzard stones in adult White-tailed Ptarmigan (Lagopus

leucurus^ in Colorado. Arctic Alpine Res. 5:49-57.

McCANN, L. J. 1939. Studies of the grit requirements of certain upland game birds. J. Wildl.

Manage. 3:31-41.

McCann, L. J. 1961. Grit as an ecological factor. Am. Midi. Nat. 65:187-192.

Meinertzhagen, R. 1954. Grit. Bull. Br. Omithol. Club 74:97-102.

Meinertzhagen, R. 1964. Grit, p. 341-342. In A. L. Thomson [ed.], A new dictionary of birds.

McGraw-Hill, New York.

Myrberget, S., C. NORRIS, and E. NORRIS. 1975. Grit in Norwegian Lagopus spp. Norw. J.

Zool. 23:205-212. Norman, F. I., and R. S. Brown. 1985. Gizzard grit in some Australian waterfowl. Wildfowl

36:77-80.

NORRIS, E., C. NORRIS, and J. B. Steen. 1975. Regulation and grinding ability of grit in the

gizzard of Norwegian Willow Ptarmigan (Lagopus lapopus>. Poult. Sd. 54:1839-1843.

Pfedfer, S., and W. Keil. 1962. Untersuchungen fiber Populationsdynamikund

Em ^rungsbiologie des Haussperlings (Passer domesticusi in hessischen Getreideanbaugebieten. Festschr. VogelschutzwartefCir Hessen, Rheinland-Pfalz und Saarland, 122-139.

pinowska, B. 1975. Food of female House Sparrows (Passer domesticus L.) in relation to stages of

the breeding cycle. Pol. Ecol. Stud. 1:211-225.

PiNOWSKA, B., AND K. Krasnicm. 1985. Quantity of gastroliths and magnesium and caldum

contents in the body of female house sparrows during their egg-laying period. Zesz.

Nauk. Filii UW, 48, Biol. 10:125-130.

porkert, J. 1972. (On the change of grit in our grouse [Tetraonidae].) Vestn. Cesk. Spol. Zool.

36:134rl59.

Reaumur, R. A. F. de. 1756. Sur la digestion des oiseaux. Premier Memoire. Experiences sur la

mani&re dont se fait la digestion dans les oiseaux qui vivent principalement de grains et herbes, et dont I'estomac est un gSsier. MSm. Acad. Sd. Paris 1752:266-307.

Robel, R. J., and A. R. Bisset. 1979. Effects of supplemental grit on metabolic effidency of

bobwhites. Wildl. Soc. BuU. 7:178-181.

Roland, D. A., Sr., D. R. Sloan, AND R. H. Harms. 1972. Caldum metabolism in the laying

hen. I. Calcium retention in the digestive tract of the laying hen. Poult. Sd. 51:598-601.

Sadler, K. C. 1961. Grit selectivity by the female pheasant during egg production. J. Wildl.

Manage. 25:339-341. 34

Siegfried, W. R. 1973. Summer food and feeding of the ruddy duck in Manitoba. Can. J. Zool.

51:1293-1297.

Smith, H. H., and R. N. Rastall. 1911. Grit, p. 94-99. ]ta A. S. Leslie [ed.]. The grouse in

health and in disease. Smith Elder, London.

Smtih, R. E. 1960. The influence of size and surface condition of grit upon the digestibility of feed

by the domestic fowl. Can. J. Anim. Sd. 40:51-56.

Smith, R. E., AND T. M. MacIntyre. 1959. The influence of soluble and insoluble grit upon the

digestibility of feed by the domestic fowl. Can. J. Anim. Sd. 39:164-169.

Spallanzani, L. 1783. Experiences sur la digestion de I'homme et de differentes especes

d'animaux. Barthelemi Chirol, Libraire, Gendve.

Tagami, S. 1974. On the variation of retention and form of grit in gizzard of growing chicks. Sd.

Rep. Faculty Agric.,Ibaraki Univ. 22:7-13.

Taylor, T. G. 1970. The provision of caldum and carbonate for laying hens, p. 108-117. In H.

Swan and D. Lewis [eds.], Proc. Univ. Nottingham Fourth Nutrition Conf. for Feed

Manufacturers. J. and A. Churchill, London.

Trrus, H. W. 1955. The sdentific feeding of chickens. 3rd ed. Interstate Press, Danville, IL.

TroST, R. E. 1981. Dynamics of grit selection and retention in captive Mallards. J. Wildl.

Manage. 45:64-73.

U.S. Dep. Agric. 1992. Agricultural chemical usage: 1991 field crops survey. U.S. Dep. Agric.,

Econ. Res. Serv., Washington, D.C.

Walter, E. D., and J. R. Attken. 1961. The value of soluble and insoluble grit in all-mash and

mash-grain rations for caged layers. Poult. Sd. 40:904-909. 35

Figure Captions:

Figure 1. Grit Retention Experiments. Values represent percentages (R+SE) of the gizzard grit that were of the first grit type given, expressed as a function of the number of days after substituting the second grit type for the first.

a. Quartz-to-Feldsparand Feldspar-to-QuartzExperiments b. Diet Experiment c. Grit Size Experiment d. Short Intervals Experiment 36

• Plant Diet • Quartz to Feldspar o Animal Diet o Feldspar to Quartz

0 5 10 15 20 25 30

100'

O) • Small Grit ° Large Grit

0 5 10 15 20 25 30 Days after Substitution Days after Substitution

Figure 1 37

CHAPTER IV, EFFECTS OF SURFACE TEXTURE AND SHAPE ON GRIT SELECTION BY HOUSE SPARROWS AND NORTHERN BOBWHITE

A paper published in The Wilson Bulletin^

Louis B, Best and James P. Gionfriddo

ABSTRACT.~We evaluated the influence of surface texture and shape on grit selection

(choice) by House Sparrows ^Passer domesticus) and Northern Bobwhite (Colinus virginianus).

Captive birds were given a mixture of two grit types (angular/oblong and rounded/spherical) for 7 or 14 days. At the end of this period, most birds (24 of 30 House Sparrows and 21 of 26 Northern

Bobwhite) had more angular/oblong and less rounded/spherical grit (P < 0.01) in their gizzards than predicted on the basis of availability. An improved understanding of avian responses to surface texture, shape, and other grit characteristics may be useful in reformulating granular pesticides to

reduce their attractiveness to birds,

INTRODUCTION

Granular pesticides are used extensively for insect control, and many are acutely toxic to

birds (e.g,, Balcomb et al. 1984, Hill and Camardese 1984), One potential route of avian exposure

to granular pesticides involves birds' intentional consumption of granules as a source of grit, A

better understanding of factors influencing grit preferences may suggest ways to alter granular

^Reprinted with permission from The Wilson Bulletin 1994,106:689-695, Copyright ® 1994 The

Wilson Bulletin, 38 formulations to reduce their attractiveness to birds and lower the probability that granules will be consumed by birds.

Few data are available on the process of grit selection by birds (e.g., Sadler 1961). Grit choice is probably influenced by physical characteristics of grit particles, such as size, color, surface texture, and shape. We evaluated the influence of surface texture and shape on grit selection by

House Sparrows (Passer domesticus) and Northern Bobwhite (Colinus virginianus). These species were chosen for experiments because they are ground-foraging granivores and omnivores, respectively (De Graaf et al. 1985), and thus they represent the feeding guilds of birds most likely to be exposed to granular pesticides. The House Sparrow also was chosen because it uses a large amount of grit compared with other birds (Keil 1973, Best and Gionfriddo 1991, Gionfriddo and

Best 1995).

METHODS

Free-ranging House Sparrows were captured with mist nets at several rural sites in Story

County, Iowa. They were fitted with numbered, aluminum leg bands, transferred to an outdoor aviary, and given at least 8 days to acclimate to captivity. Gizzards of House Sparrows then were voided by saline flushing. Each bird was anesthetized by injecting the pectoral muscle with 0.15 cc of ketamine hydrochloride (Vetalar®, diluted to 10 mg/ml) to which about 0.005 cc of diazepam

(Valium®, 5 mg/ml) had been added. We then flushed the gizzard with 30 cc of saline solution

(0.9% sodium chloride irrigation, USP), delivered in 20 1.5-cc injections. We used a 10-ml

Cornwall S5ninge pipet with a ball-tipped, straight intubation needle (18 gauge, 7.6 cm long). The needle was long enough to reach a House Sparrow's gizzard when inserted through the mouth.

Gizzard contents were hydraulically flushed through the esophagus and mouth, while the bird was 39 held in a vertical position, tail up and beak down. This procedure effectively removes all or nearly all food and grit from the gizzards of most House Sparrows, and the recovery rate of the birds is

high (92%) (Gionfriddo et al., 1995). After recovery from anesthesia, 30 birds were placed in an

aviary compartment with food and water. The experiment began when grit was added at dawn

the next day.

Juvenile (11-week-old) Northern Bobwhite were purchased from a commercial game bird

producer (Pine Creek Came Farms, Montrose, lA) and transferred to our aviaries where they were

held for 18 weeks before being used in the experiment. There was no need to void gizzards of the

Northern Bobwhite because grit had been withheld from these birds since hatching.

During acclimation and experiments. House Sparrows and Northern Bobwhite were

housed in outdoor aviary compartments measuring 3.7 x 4.6 x 2.1 m and maintained on a

commercially prepared wild bird seed mixture (Cardinal Brand Wild Bird Feed, Des Moines Feed

Co., Des Moines, LA) containing millet, milo, cracked com, sunflower seeds, peanuts, and wheat.

Birds also were provided with vitamin-enriched water. Grit was provided only during

experiments.

Two types of grit were used, representing two extremes in surface texture/shape. For

House Sparrows, rounded/spherical grit consisted of "blanks" of silica (quartz) granules used for

the pesticide FURADAN15G, and angular/oblong grit was hammermilled "Colorado quartz" (Fig.

1). (Best and Gionfriddo [1991] described the system used to characterize grit surface

texture/shape; surface textures ranged from well-rounded to angular and shapes from spherical to

oblong.) For Northern Bobwhite, clear glass beads were used as rounded/spherical grit, and

angular/oblong grit was hammermilled clear glass. For both species, the two grit types were

identical in mineral composition (quartz or glass), color (clear), and size (both grit types were 40 sieved to a size range of 0.4 - 0.8 mm for House Sparrows and 1.8 - 2.4 mm for Northern

Bobwhite; these sizes represent the middles of the normal ranges of grit sizes used by free-ranging birds of these two species [Best and Gionfriddo 1991]). All grit was tumbled in a vibrating tumbler for 5 days to produce a "frosted" surface similar to that of the silica granules, and to dull the jagged edges of the hammermilled grit.

Grit was provided to birds during each experiment in two square grit trays, each measuring 0.5 m^. Sides of the trays were constructed of 2 x 4" lumber (5 x 10 cm), and bottoms consisted of the cement aviary floor. Each tray contained a mixture of equal amounts (by volume) of angular/oblong and rounded/spherical grit. Volumetric measures of grit were used because the large amounts of grit needed in the experiments precluded our counting individual particles provided to birds and necessitated the use of an alternative measure. Each tray was supplied with

10 cc (House Sparrows) or 25 cc (Northern Bobwhite) of grit, which was replaced every 2 days.

Later, we counted the particles in equal volumes of angular/oblong and rounded/spherical grit to determine the proportions (in numbers) of the two grit tjrpes in the grit mixtures given to Northern

Bobwhite and House Sparrows. Ratios of angular/oblong to rounded/spherical grit were 53:47 for

Northern Bobwhite and 35:65 for House Sparrows. These ratios were then used in deriving expected values for Chi-square analysis.

In the House Sparrow experiment, all (30) birds were sacrificed after 14 days; in the

Northern Bobwhite experiment, half of the 26 birds were sacrificed after 7 days, and half after 14 days. Gizzards were removed and preserved in 95% ethanol. Later, each gizzard was sliced in half with a razor blade, and the contents were flushed into a petri dish and examined carefuUy under a zoom, stereo microscope. Grit particles were separated from other gizzard contents; 41 contents were searched thoroughly at least two times. Grit particles of the two t5rpes were then sorted and counted.

RESULTS

All House Sparrows readily consumed the grit provided. The mean grit count per bird was 139.5 (+ 82.5 [SD]), well within the range of values for free-ranging House Sparrows

(Gionfriddo and Best 1995). Twenty-four of 30 birds had greater proportions of angular/oblong grit in their gizzards than if they had consumed grit randomly (Chi-square analysis, P < 0.01); three had significantly more rounded/spherical grit (Fig. 2). Only three birds had no apparent grit surface texture/shape preference. Ratios of angiilar/oblong to rounded/spherical particles in these three gizzards did not differ from 35:65.

Gizzard contents of Northern Bobwhite given grit for 7 days were similar to those of 14- day birds. All birds in both groups consumed grit, and mean grit counts per bird did not differ between groups (t = 0.12, df = 23, P = 0.91; 7-day birds: x = 145.5 ± 81.6,14rday birds: x = 148.9 ±

68.8). Furthermore, the proportion of the grit particles that were angular/oblong did not differ between gizzards of the two groups of birds (t = 1.68, df = 19, P = 0.11). Consequently, the 7-day and 14-day data sets were combined. Twenty-one of 26 gizzards contained greater proportions of angtilar/oblongthan rounded/spherical grit, and 1 gizzard contained more rounded/spherical grit

(Chi-square analysis, P < 0.01). Proportions of the two grit t)^es in the remaining 4 gizzards did not differ significantly. 42

DISCUSSION

The House Sparrows and Northern Bobwhite used in our experiments differed in several ways. The House Sparrows were formerly free-ranging birds experienced in using grit, whereas the Northern Bobwhite were captive-raised juveniles never exposed to grit. The two species also are very different in body size and represent different avian orders. Despite these differences, the responses of House Sparrows and Northern Bobwhite were very similar in our experiments. Both species clearly expressed a preference for angular/oblong rather than rounded/spherical grit when given a mixture of the two types. The occurrence of this preference in birds with prior experience in grit use and in birds with no prior exposure to grit suggests the preference may have a genetic basis.

Grit preferences may be related to diet. The amounts, sizes, and shapes of grit used by birds vary with diet (e.g., Norris et al. 1975, Alonso 1985, Norman and Brown 1985, Hogstad 1988).

Perhaps certain grit surface textures/shapes increase the efficiency of digestion of some foods more effectively than others. Based on examination of grit. Smith and Rastall (1911) suggested that Red

Grouse ^Lagopus 1. scoticus) needed "sub-angular and roughly rounded" small pebbles to grind foliage of Calluna. and that grit with cutting edges and sharp points was unsuitable. The House

Sparrows and Northern Bobwhite may have selected angular/oblong grit because it more efficiently

ground the seeds they ate. The degree to which diet influences grit selection has not been tested

formally.

Grit present in a bird's gizzard depends not only upon selection of particles for

consumption, but also upon the dynamics of retention in the gizzard. Grit selection, as we have

measured it here, thus includes a component of grit retention. Particle characteristics such as

surface texture and shape may influence retention of grit. We conducted other experiments with 43 captive House Sparrows to evaluate the relative contribution of grit-retention processes to the surface texture/shape of grit present in gizzards (Best and Gionfriddo, unpubl. data). Birds were administered (oral gavage) or fed (mixed with canned dog food) equal amounts of the angular/oblong and rounded/spherical grit for a period of time, deprived of grit for 2 days, and then sacrificed. In both experiments, the proportions of the two grit types did not differ (Chi- square analysis, P > 0.5) in most gizzards. The results of these retention experiments suggest that surface texture/shape may not influence grit retention. We conclude that the grit-use patterns observed in gizzards of experimental House Sparrows and Northern Bobwhite reflect differential selection (rather than differential retention) of angular/oblong and rounded/spherical particles.

Although grit selection may be the primary factor determining the grit in birds' gizzards, it can be constrained by avaUability of grit of various types. Grit selection also may be affected by diet, characteristics of grit already in the gizzard, and other factors. More experimental work is needed, with additional avian species, before we will have a clear understanding of avian grit preferences and of the influences of grit characteristics such as surface texture/shape on grit choice and retention in birds. Such knowledge may be useful in "designing" granular pesticides to make

them less attractive to birds.

ACKNOWLEDGMENTS

B. J. Giesler captured the House Sparrows and maintained all birds for experimental use,

and B. J. Giesler, L. D. Igl, and B. C. Schoeberl assisted in the laboratory work and data tabulation.

C. E. Braun and D. L. Fischer reviewed earlier drafts of the manuscript and offered helpful

suggestions. Funding was provided by Miles, Inc., Rh6ne-Poulenc, American Cyanamid, and 44

Dow Elanco. This is Journal Paper No. J-15004 of the Iowa Agriculture and Home Economics

Experiment Station, Ames, Project 2168.

LITERATURE CITED

ALONSO, J. C. 1985. Grit in the gizzard of Spanish Sparrows fPasser hispaniolensisl. Vogelwarte

33:135-143.

Balcomb, R., R. Stevens, and C. Bowen n. 1984. Toxicity of 16 granular insecticides to

wild-caught songbirds. Bull. Environ. Contam. Toxicol. 33:302-307.

Best, L. B. and J. P. Gionfriddo. 1991. Characterization of grit use by cornfield birds. Wilson

Bull. 103:68-82.

De Graaf, R. M., N. G. Tilghman, and S. H. Anderson. 1985. Foraging guilds of North

American birds. Environ. Manage. 9:493-536.

Gionfriddo, J. P., and L. B. Best. 1995. Grit use by House Sparrows: effects of diet and grit size.

Condor, in press.

Gionfriddo, J. P., L. B. Best, and B. J. Giesler. 1995. A saline flushing technique for

determining the diet of seed-eating birds. Auk, in press.

Hill, E. F. and M. B. Camardese. 1984. Toxicity of anticholinesterase insecticides to birds:

Technical grade versus graniilar formulations. Ecotoxicol. Environ. Safety 8:551-563.

hogstad, O. 1988. Foraging pattern and prey selection of breeding Bramblings Fringilla

montifringilla. Fauna Norv. Ser. C, Cinclus 11:27-39.

Keil, W. 1973. Investigations on food of House- and Tree Sparrows in a cereal-growing area

during winter. Pp. 253-262 in Productivity, population dynamics and systematics of 45

granivorous birds (S. C. Kendeigh and J. Pinowski, eds.). PWN - Pol. Sd. Publ.,

Warszawa.

Norman, F. I. and R. S. brown. 1985. Gizzard grit in some Australian waterfowl. Wildfowl

36:77-80. norris, E., C. norris, and J. B. sxeen. 1975. Regulation and grinding ability of grit in the

gizzard of Norwegian Willow Ptarmigan (Lagopus lagopus^. Poult. Sd. 54:1839-1843.

Sadler, K. C. 1961. Grit selectivity by the female pheasant during egg production, J. Wildl.

Manage. 25:339-341.

Smith, H. H. and R. N. Rastall. 1911. Grit. Pp. 94-99 in The grouse in health and in disease

(A, S. Leslie, ed.). Smith Elder, London. 46

Figure Captions:

Figure 1. Angular/oblong and rounded/spherical grit used in experiments with House Sparrows

(left) and Northern Bobwhite (right).

Figure 2. Angular/oblong and rounded/spherical grit particles in gizzards of House Sparrows and

Northern Bobwhite given a mixture of the two types of particles. Asterisks denote birds that consumed one grit particle type in proportions greater than expected on the basis of its availability

(Chi-square analysis, P < 0.01). 47

Figure 1 48

House Sparrow

•Angular/Oblong HI Rounded/Spherical

*1

Northern Bbbwhite

•Angular/Oblong m Rounded/Spherical

300 250 200 150 100 50 0 50 100 150 200 250 300 Number of Grit Particles

Figure 2 49

CHAPTER V. GRTT COLOR SELECTION BY HOUSE SPARROWS AND NORTHERN BOBWHITES

A paper submitted to the Journal of Wildlife Management

James P. Cionfriddo and Louis B. Best

ABSTRACT: One potential route of avian exposure to granular pesticides is the consumption of granules mistakenly picked up as grit. Granule color may be an important factor influencing avian exposure to granular pesticides, and is one of the most easily altered characteristics of pesticide granules. We studied colored grit use by house sparrows (Passer domesticus^ and northern bobwhites fColinus virginianus') by offering captive birds a grit mixture consisting of equal amounts of 8 colors (red, brown, yellow, green, blue, black, white, clear), either on a light-brown or a dark- brown soil background. Gizzard contents of both species indicated that birds consistently were nonrandom in their consumption of colored grit. In gizzards of both house sparrows and northern bobwhites, yellow, green, and white particles represented the greatest proportions of colored grit.

Both species generally used very little black or blue grit. Soil background color had only a slight influence on grit color selection, and only in house sparrows. To examine the influence of food color on grit color selection, we repeated the experiments (on dark soil only), using birds maintained on food dyed to match 3 of the 8 grit colors (red, yellow, blue). Grit color use again was nonrandom. Overall, house sparrows preferred brown, yellow, and white grit, and northern bobwhites preferred yellow and green grit. Black again received little use by both species. Food color affected grit color selection in both species, but was not associated with major differences in the preference rankings of the 8 grit colors. Grit color use by males and females did not differ in either species in any of the experiments. Our results suggest that the colors black and blue should 50 be tested further if the goal is to design pestidde granules in colors unattractive to birds. On the other hand, if the goal is to design granules to attract birds and induce consumption for aversive conditioning, then yellow (and perhaps white and green) should receive further study.

INTRODUCTION

Granular pesticides are applied to millions of acres of com and other crops in the United

States each year to control com rootworms and other agricultural pests (U.S. Dep. Agric. 1992).

Pesticide granules are often spilled or not fully incorporated into the soil during application, making them accessible to birds. Because many of these products are highly toxic to birds

(Balcomb et al. 1984, Hill and Camardese 1984), there is much interest in the evaluation of avian risks associated with granular pesticide use. Risk is a function of many factors, including those that influence the likelihood of avian exposure to pesticide granules. Among the factors affecting the probability of exposure are birds' behavioral responses to granules when they are encountered.

One potential route of avian exposure to granular pesticides is the consumption of granules mistakenly picked up as a source of grit (Best and Fischer 1992). Some pestidde granules are similar to natural grit particles in physical characteristics such as size, shape, surface texture, color, and mineral composition (Best and Gionfriddo 1991a,b; Best 1992). These physical features may strongly influence the probability that birds notice and ingest the granules. An understanding of the granule characteristics that influence avian responses could be useful in designing pestidde granules less likely to be consumed in lethal doses by birds.

Granule color may be an important factor influencing avian exposure to granular pestiddes, and it is one of the most easily altered characteristics of pestidde granules (Best and

Fischer 1992). Granular pestiddes are manufactured in many colors, induding bright, vivid hues.

Avian color vision is highly developed, and some birds have expressed distinct color preferences in 51 experimental situations (e.g., Hailman 1966, Branner and Coman 1983, Roper and Cook 1989).

Although it is not known if birds exhibit color preferences in their selection of grit, Meinertzhagen

(1964) suggested that brightly colored grit is preferred to dull. Sufficient data are not available to test this hypothesis, however, because grit color is rarely mentioned in published reports of avian grit use. Grit used by birds varies greatly in color, ranging from clear (colorless) to black (Best and

Gionfriddo, pers. observ.). The predominance of opaque grays, light browns, and off-whites we found in gizzards may simply reflect the greater availability of these hues.

The visibility or conspicuousness of a grit particle is influenced by the particle's color and its contrast with the background. A particle might cryptically "disappear" on one soil background but be highly conspicuous on another. Meaningful assessment of avian responses to grit particles of various colors, therefore, requires consideration of the effects of background color. Examination of avian responses to colored grit particles placed on backgrounds of different colors may reveal general patterns of color preference or avoidance, as well as the influence of background color on such patterns.

We tested avian responses to colored grit by presenting house sparrows and northern bobwhites with a mixture of 8 colors of grit on either a light-colored or a dark-colored soil surface.

We selected the house sparrow and northern bobwhite as experimental species because they are ground-foraging omnivores and granivores, respectively, and thus they represent the feeding guilds of birds most likely to be exposed to granular pesticides. These 2 species also provide a good contrast, in that they are not closely related and they differ in mean body mass by a factor of

6. Soil colors were chosen to represent 2 very different agricultural soils to which pesticide granules might be applied. To examine the influence of food color on grit color selection, we 52 repeated the experiments, using birds maintained on food dyed to match 3 of the 8 grit colors (red, yellow, blue [primary hues]).

METHODS

Initial Experiments

Free-ranging house sparrows were captured with mist nets at several rural sites in central

Iowa. Northern bobwhites were purchased from a commercial game bird producer (Pine Creek

Game Farms, Montrose, la.). Birds were fitted with numbered, aluminum leg bands and transferred to outdoor aviaries where they were acclimated to captivity before being used in experiments. During acclimation and experiments, birds were maintained on a seed mixture consisting of millet, milo, cracked com, sunflower, peanuts, and wheat (Cardinal Brand Wild Bird

Feed, Des Moines Feed Co., Des Moines, la.).

Birds were assigned randomly to experimental treatments (soil colors), except that an effort was made to balance the sex ratio within each replicate group. A replicate group consisted of 32 house sparrows (or 35 northern bobwhites) assigned to the same experimental treatment and placed together in an aviary compartment measuring 3.7 x 4.6 x 2.1 m, where they were given food, water, and grit. For each soil color, there were 3 replicate groups of each avian species. In each aviary compartment, grit was provided to birds in 2 grit trays, each measuring 1 The bottoms of the trays were covered with either light-colored or dark-colored soil. The light-colored soil was light yellowish brown loess collected from Marshall County, Iowa, and the dark soil was dark grayish brown topsoil from a cornfield in Story County, Iowa (soil colors from Munsell Soil

Color Classification System [Anonymous 1988]). To produce a "crusted" soil surface that would deter colored grit particles from quickly becoming buried in the very fine soil (sieved to < 0.3 mm). 53 we liberally sprayed a 1:1 mixture of all-purpose white glue and water on the soil and allowed it to dry*

Grit in these experiments consisted of colored, opaque glass that was hammermilled and then tumbled in a vibrating tumbler to dull sharp edges and simulate the effects of natural erosional processes. Glass was chosen as a substitute for natural grit because it is available in a wide range of colors and is very similar to grit in many physical characteristics. It is compositionally similar to quartz, the mineral most commonly used as grit by free-ranging birds

(e.g., Korschgen 1964, May and Braun 1973, Selden and Smith 1978). The colored glass was then sieved to a size range of 0.4 - 0.8 mm for house sparrows or 0.8 - 2.0 mm for northern bobwhites.

These size ranges were selected because they straddle the midpoints of the normal ranges of grit sizes used by free-ranging house sparrows and northern bobwhites (Best and Gionfriddo 1991a).

Before beginning the colored grit experiments, we conducted a preliminary experiment in which house sparrows were fed gelatin capsules containing hammermilled glass. We found that no gizzard damage resulted from the use of glass as a substitute for natural grit. Another preliminary experiment demonstrated that house sparrows voluntarily consumed clear glass particles as readily as clear quartz when given a mixture of the 2 (Best and Gionfriddo, unpubl. data).

In the Initial Experiments, a mixture of equal amounts (by volume) of 8 colors of glass was

used: deep red, vivid yellow, moderate green, vivid purplish blue, strong brown, black, white, and clear. These colors were classified according to the universal color language adopted by the U.S.

Bureau of Standards (U.S. Dep. Commerce 1976). Except for their color, the grit particles were

similar in many physical characteristics including size, shape, surface texture, hardness, and

specific gravity. An ad libitum supply of each color of grit was made available to the birds

throughout the experiments by sprinkling 15 cc of the grit mixture into each grit tray daily, after 54 using a portable vacuum cleaner to remove leftover grit from the previous day. After 7 days, experimental birds were euthanized, and their gizzards were removed and preserved in 95% ethanol.

In the laboratory, each gizzard was sliced in half with a razor blade. Gizzard contents were flushed into a Petri dish and examined under a zoom stereomicroscope. The grit particles found in each gizzard were sorted by color and then counted. Gizzards containing fewer than 10 colored grit particles were excluded from the analysis.

For each house sparrow and northern bobwhite, we used chi-square analysis to test the hypothesis that the bird used all 8 colors of grit in equal proportions. Multivariate analysis of variance (MANOVA) was used to determine the effects of sex, soil color, and replicate group on bird use of the 8 grit colors. Univariate analysis of variance was used to determine which variables contributed to the overall differences detected by the MANOVAs. To satisfy the assumption of normality, we based all analyses of variance on the arcsine transformation of the color proportions

(Zar 1984:168). Individual birds were the experimental units. Among house sparrows, preliminary analysis detected no significant differences between juveniles and adults, so the age classes were combined. All northern bobwhites were juveniles.

Colored Food Experiments

Two of the grit colors preferred by birds in the Initial Experiments (see Results) were similar to the predominant colors of the seeds fed to the captive birds. To test if we had inadvertently conditioned or trained the birds to consume particles of these colors, we repeated the

experiments, using a dry mash feed (Purina Game Bird Flight Conditioner, Purina Mills, St. Louis,

Mo.) that could be colored with food coloring. (Seeds could not be dyed uniformly.) By sprajring

the dry mash with a 15:1 mixture of water and food coloring, and then drjring it in a warm oven. 55 we produced red, blue, and yellow food, matching the corresponding grit colors as closely as possible. These colors were chosen to represent grit that had received heavy (yellow), moderate

(red), and light (blue) use in the Initial Experiments. Birds of each sex were randomly assigned to treatments (food colors). For each food color, there were 3 replicate groups of each avian species.

The 35 birds in each replicate group were given either red, blue, or yellow food for 14 days. Grit trays containing the mixture of 8 colors of grit were added after the first 7 days, and the grit was replaced daily. Only dark soil was used as a background substrate in grit trays in the Colored

Food Experiments because we had found few significant differences in grit color use on the 2 soil backgrounds by house sparrows and none by northern bobwhites in the Initial Experiments. Also, dark soils predominate on agricultural lands where granular pesticides receive the widest use (Wis.

Agric. Exp. Stn. 1960). At the end of the experiments, birds were euthanized, their gizzard contents examined, and the grit sorted by color and counted.

RESULTS

Initial Experiments

Captive house sparrows and northern bobwhites readily accepted the colored glass grit, and chi-square analysis revealed that their responses to the 8 grit colors were consistendy nonrandom. Gizzards of all but 2 of the 161 house sparrows and all but 1 of the 210 northern bobwhites contained the 8 grit colors in unequal proportions (individual P-values for the 159 house sparrows: P < 0.025; for the 209 northern bobwhites: P < 0.001). Gizzards of 31 of the 192 house sparrows (29 light- and 2 dark-soil) contained fewer than 10 colored grit particles and were excluded from the analysis.

MANOVA detected an interaction between soil color and sex that affected house sparrow

responses to the 8 grit colors (Eg 142 = 2.92, P = 0.005). When compared with birds in the other 3 56 soil-color/sex groups, male house sparrows on light soil consumed less green grit, and more white and clear grit (as proportions of all colored grit). Gizzards of female house sparrows on light soil contained more green and less white grit than those of house sparrows in the other 3 soil-color/sex groups (females on dark soil, males on dark soil, males on light soil). The independent effects of soil color and sex also influenced house sparrow responses (soil: £3142 = 2.33, P = 0.022; sex: Eg 142

= 3.23, P = 0.002), although univariate analyses detected no significant (P > 0.067) effect of soil color on the use of any of the 8 grit colors. Male house sparrows consumed more white grit than females. In the northern bobwhite experiment there was no interaction between soil color and sex that affected birds' responses to colored grit (Eg.wi 0*69, P = 0.697), and neither factor independenfly affected birds' responses (soil: Fg.iQi ~ E " 0*174; sex: = 1.30, P = 0.243).

Northern bobwhite responses to colored grit differed among replicate groups for each soil color

(F32 758 = 1.96, P = 0.001); house sparrow responses did not (£32,552 ~ 1*^®' £ ~ 0.054). Although significant statistically, the northern bobwhite differences were relatively small in the context of the overall patterns of colored grit use by bobwhites, and did not substantially affect the overall preference rankings of the 8 grit colors.

In gizzards of house sparrows in both light and dark soil treatments, green, yellow, and white grit particles represented the greatest proportions of the colored grit (Fig. 1). Northern bobwhite responses to the colored grit were similar to those of house sparrows. On both light and dark soils, yellow and white grit received the heaviest use; green grit also was used heavily in 3 of the 6 replicates (Fig. 1). In both the sparrows and bobwhites, black and blue particles made up the smallest proportions of colored grit in gizzards.

Many birds evidently focused their grit consumption on particles of 1 or a few colors.

"Favored" color(s) varied among individual birds, but some grit colors were preferred by more 57 birds than others. Yellow grit, for example, represented the greatest proportion of the colored grit in nearly 3* (37 of 161) of the house sparrow gizzards and in nearly Jj (92 of 210) of the northern bobwhite gizzards. White was the most common grit color in 38 house sparrow and 48 northern bobwhite gizzards. Even colors least favored overall were the most favored by some individuals.

Blue, for example, was the most common grit color in 10 house sparrow and 5 northern bobwhite gizzards, and black was the most common color in 2 gizzards of each avian species.

Colored Food Experiments

In the Colored Food Experiments, house sparrows and northern bobwhites readily and nonrandomly consumed the colored glass grit. Only 3 of 576 gizzards (2 house sparrow and 1 northern bobwhite) contained particles of the 8 colors of grit in approximately equal proportions

(chi-square analysis, P > 0.001).

Food color and sex interacted to influence the selection of colored grit by northern bobwhites (Ejg 524 = 1.92, P = 0.016) but not by house sparrows (Fjg 524 = 1.18, P = 0.276).

Specifically, the proportions of red grit and brown grit in gizzards of northern bobwhites that had consumed yellow food were relatively high among males and low among females. In both avian species, food color independently affected grit color selection (house sparrow: Ejg 524 = 3*09/ P <

0.001; northern bobwhite: Fjg 524 = 9.63, P < 0.001) but sex did not (house sparrow: £3 253 = 0.75, P

= 0.643; northern bobwhite: £3 263 " — ~ 0.271). Among house sparrows, contrary to expectation, the consumption of yellow grit was greater in birds given red food than those given yellow food (Fig. 2). On the other hand, as expected, house sparrow consumption of blue and

black grit was greater in birds fed blue food. Among northern bobwhites, food color exerted a

significant (P < 0.012) effect on the use of 6 of the 8 grit colors (all but yellow and white). In all 6 instances, the responses of birds consuming blue food differed from those of birds fed red and 58 yellow food. In the context of the overall pattern of northern bobwhite colored grit use, however, these differences were relatively small. Replicate groups differed in their responses to colored grit in house sparrows (E484568 2.81, P < 0.001) and northern bobwhites (£48,1568 ~ 2,43, P < 0.001).

Grit-use differences among food repUcate groups, like those among soil-color replicate groups in the northern bobwhite Initial Experiments, were relatively minor and had no meaningful efifect on the relative preference rankings of the 8 grit colors.

As in the Initial Experiments, there was great variation among individual birds, but several overall patterns in grit color use emerged. Among house sparrows, yellow and white again were favored colors, and black and blue grit receive the least use (Fig. 2). Green grit, which had been used heavily in the Initial Experiments, received only moderate use by house sparrows given colored mash. On the other hand, brown grit showed the opposite shift in use, and was the overall favored grit among house sparrows consuming colored mash. Overall, yellow and green grit received the greatest use by northern bobwhites. For bobwhites, the results of the Colored

Food Experiments were similar to those of the Initial Experiments, except that white grit, which was favored in the earlier experiments, received relatively little use by birds fed colored mash.

DISCUSSION

Grit color choice in birds may be influenced by innate and/or learned preferences and aversions for specific colors and by the relative conspicuousness of various grit colors against a given soil background. Many experimental efforts to identify innate avian color preferences have tested the pecking responses of newly hatched birds presented with a choice of colored, illuminated keys (or colored chips) in a test box. In such tests, domestic chicks (Gallus gallus^ have shown preferences in the red-orange and blue-violet regions of the visible spectrum (e.g., Hess

1956, Fischer et al. 1975, Fischer and Davis 1981). On the other hand, newly-hatched Japanese 59 quail fCotumix japonica'i generally have preferred green and yellow, and avoided red and blue

(Kovach 1974, Duecker and Schulze 1977), a pattern consistent with the selection of colored grit by our juvenile northern bobwhites (Figs. 1,2).

Early avian color preferences may be modified by experience (e.g., Rabinowitch 1968,

Brunner and Coman 1983, Roper 1990), and the influences of innate factors and learning on the color responses of adult birds often are indistinguishable. Much of the research examining the

color preferences of adult birds has been prompted by a desire to reduce avian depredation of

grain crops or to reduce avian consumption of toxic baits intended for rodents. Accordingly, its focus often has been on avian preferences for foods of various colors. Although preferences seem

to vary greatly, a consistent finding of studies in which artificially-colored grain or other seeds were

offered to free-ranging birds was an avoidance of green, blue, and black items (Kalmbach and

Welch 1946, Pank 1976, Slaby and Slaby 1977, Brunner and Coman 1983, Bryant et al. 1984).

Similarly, blue and black grit generally received relatively little use in our experiments with captive

house sparrows and northern bobwhites (Figs. 1,2).

Color may influence particle conspicuousness in 2 ways. Some colors may be inherently

conspicuous to birds, regardless of context (Sill§n-Tullberg 1985, Roper and Cook 1989, Roper 1990). Conspicuousness also may depend on the degree of contrast with the background

(Gittleman and Harvey 1980, Gendron 1986). In our experiments, some grit colors seemed much

more conspicuous (to humans) on 1 of the 2 soil backgrounds, and yet we found only a limited

influence of soil color on grit color selection, and only in house sparrows. Pank (1976) tested the

effects of seed-coloring agents and background color on Douglas fir (Pseudotsupa menziesii^ seed

acceptance by 3 species of granivorous birds and concluded that background color did not affect 60 colored- seed selection. Additional research is needed to clarify the influence of background color on avian color preferences.

The causes of the observed differences in house sparrow use of green and brown grit in our Initial and Colored Food Experiments (Figs. 1,2) are unknown, but may be related to the seasonal timing of the experiments. The house sparrow Colored Food Experiment was conducted during winter (Dec-Feb); all other experiments occurred in summer and early fall (Aug-Oct).

Seasonal variation in lighting conditions in the aviaries (which faced south) may have affected

house sparrow grit color selection. An alternative explanation is that if food color influences grit

color selection, then the observed house sparrow preference shift from green grit in fall to brown

grit in winter may reflect similar seasonal changes in the colors of seeds house sparrows consume in the wild. The latter explanation is consistent with our finding no similar preference shift from

green to brown grit in the experimental northern bobwhites, which had been raised in captivity

and, therefore, had no experience foraging in the wild.

The possibility that food color affected grit color selection was suggested by the results of

the Initial Experiments, when the similarity between preferred grit colors (yellow and white) and

the predominant colors of the seeds consumed by the birds (off-whites, pale yellows, pale oranges)

became evident. The Colored Food Experiments confirmed that, at least for some birds, food color

influences the selection of grit colors. The extent of this influence in free-ranging birds, however,

may be very limited. Although some differences in colored grit use were statistically significant,

they were not associated with major differences in the preference rankings of the 8 grit colors (Fig.

2). Moreover, free-ranging, ground-foraging avian omnivores and herbivores are likely to consume

foods of many colors, unlike our experimental birds, whose food color remained constant for 2

weeks. 61

MANAGEMENTIMPLICATIONS

There are 2 approaches to manipulating pesticide granule color to reduce avian risk: making the granules either more attractive/visibleor less attractive/visible. Highly attractive/visible granules would be useful if the goal were to develop aversive responses in birds. Such granules would be more likely to be consumed by birds, and their conspicuous coloration could facilitate the learning of aversions (Gittleman and Harvey 1980, Gittleman et al. 1980, Mason and Reidinger

1983, Roper and Redston 1987), Aversive conditioning would be effective only for pesticide formulations with low avian toxicity per granule and for avian species capable of learning food aversions. Our results suggest that yellow (and perhaps white) should be tested further for the potential to attract birds and induce particle consumption. An advantage of making pesticide granules highly conspicuous is that spills could be more easily detected and cleaned up, reducing exposure risk for humans, livestock, and wildlife.

Making pesticide granules less attractive/visiblewould effectively reduce avian risk if an avoidance of (or an inability to easily detect) certain colors was widespread among avian species that frequent pestidde-treated areas. Gur results, consistent with the findings of avian food-color preference research, suggest that black and blue warrant additional testing for their potential to

reduce avian consumption of pesticide granules.

The success of any attempt to use color to reduce avian risk depends on the consistency of

color responses within and among the avian species exposed to granular pesticides. Although we

found several consistent, overall patterns in colored grit use by house sparrows and northern

bobwhites, the responses of individual birds varied greatly. We conclude that if the consumption

of pesticide granules as a source of grit is a major source of avian exposure, then manipulating

granule color may substantially reduce the overall risk of avian exposure, but it is not likely to 62 eliminate that risk for all birds. Investigation of the grit color responses of additional avian species is needed to identify the grit colors most (and least) likely to elicit granule discovery and consumption, and to further assess the feasibility of coloring pesticide granules to reduce avian risk.

ACKNOWLEDGMENTS

We thank K. L. Andersen, J. D. Best, J. K. Creswell, B. J. Giesler, R. P. Giesler, J. R. Gionfriddo,

L. D. Igl, J. McCarty, B. C. Schoeberl, M. K. Trzdnski, and G. Zenitsky for assisting with the lab work. J. R. Gionfriddo also assisted with data tabulation, and B. J. Giesler captured and maintained the birds and assisted with all experiments. J. J. Dinsmore, D. L. Fischer, E. E. Klaas,

J. L. Sell, and K. C. Shaw reviewed an earlier draft of the manuscript and offered many helpful suggestions. Funding was provided by Miles, Inc., Rh5ne-Poulenc, American Cyanamid, and Dow Elanco. This is Journal Paper J-15951 of the Iowa Agriculture and Home Economics

Experiment Station, Ames, Project 2168.

LITERATURE CITED

Anonymous. 1988. Munsell soil color charts. MacBethDiv. of KoUmorgen Instruments Corp.,

Baltimore, Md.

Balcomb, R., R. Stevens, and C. Bowen H. 1984. Toxicity of 16 granular insecticides to wild-caught

songbirds. Bull. Environ. Contam, Toxicol. 33:302-307.

Best, L. B. 1992. Characteristics of com rootworm insecticide granules and the grit used by

cornfield birds: evaluating potential avian risks. Am. Midi. Nat. 128:126-138.

, and D. L. Fischer. 1992. Granular insecticides and birds: factors to be considered in

understanding exposure and reducing risk. Environ. Toxicol. Chem. 11:1495-1508. 63

, and J. P. Gionfriddo. 1991a. Characterization of grit use by cornfield birds. Wilson Bull.

103:68-82.

and . 1991b. Integrity of five granular insecticide carriers in house sparrow gizzards.

Environ, Toxicol. Chem. 10:1487-1492.

Brunner, H., and B. J. Coman. 1983. The ingestion of artificially coloured grain by birds, and its

relevance to vertebrate pest control. Aust. Wildl. Res. 10:303-310.

Bryant, H., J. Hone, and P. Nicholls. 1984. The acceptance of dyed grain by feral pigs and birds.

I. Birds. Aust. Wildl. Res. 11:509-516.

Duecker, G., and I. Schulze. 1977. Color vision and color preference in Japanese quail fCotumix

cotumix japonica^ with colorless oil droplets. J. Comp. Physiol. Psychol. 91:1110-1117.

Fischer, G. J., G. L. Morris, and J. P. Ruhsam. 1975. Color pecking preferences in white leghorn

chicks. J. Comp. Physiol. Psychol. 88: 402-406.

J and S. J. Davis. 1981. Brightness effects on color pecking preferences in dark-hatched

domestic chicks. Dev. Psychobiol. 14: 237-249.

Gendron, R. P. 1986. Searching for cryptic prey: evidence for optimal search rates and the

formation of search images in quail. Anim. Behav. 34: 898-912.

Gittleman, J. L., and P. H. Harvey. 1980. Why are distasteful prey not cryptic? Nature 286:149-

150.

, , and P. J. Greenwood. 1980. The evolution of conspicuous coloration; some experiments

in bad taste. Anim. Behav. 28:897-899.

Hailman, J. P. 1966. Four color preferences of the laughing gull, Larus atricilla. Am. Zool. 6:568.

Hess, E. H. 1956. Natural preferences of chicks and ducklings for objects of different colors.

Psychol. Rep. 2: 477-483. 64

Hill, E. P., and M. B. Camardese. 1984. Toxicity of anticholinesteraseinsectiddes to birds:

technical grade versus granular formulations. Ecotoxicol. Environ. Safety 8:551-563.

Kalmbach, E. R., and J. F. Welch. 1946. Colored rodent baits and their value in safeguarding

birds. J. Wildl. Manage. 10: 353-360.

Korschgen, L. J. 1964. Foods and nutrition of Missouri and midwestem pheasants. Trans. N.

Am. Wildl. and Nat. Resour. Conf. 29:159-180.

Kovach, J. K. 1974. Early color preferences in the cotumix quail. J. Comp. Physiol. Psychol. 87:

1049-1060.

Mason, J. R., and R. F. Reidinger, Jr. 1983. Generalization of and effects of pre-exposure on color-

avoidance learning by red-winged blackbirds (Agelaius phoeniceus^. Auk 100:461-468.

May, T. A., and C. E. Braun. 1973. Gizzard stones in adult white-tailed ptarmigan (Lagopus

leucurus^ in Colorado. Arctic Alpine Res. 5:49-57.

Meinertzhagen, R. 1964. Grit. Pages 341-342 in A. L. Thomson, ed. A new dictionary of birds.

McGraw-Hill, New York, N.Y.

Pank, L. F. 1976. Effects of seed and background colors on seed acceptance by birds. J. Wildl.

Manage. 40:769-774.

Rabinowitch, V. 1968. The role of experience in the development and retention of seed

preferences in zebra finches. Behaviour 33: 222-236.

Roper, T. J. 1990. Responses of domestic chicks to artificially coloured insect prey: effects of

previous experience and background colour. Anim. Behav. 39: 466-473.

, and S. E. Cook. 1989. Responses of chicks to brightly coloured insect prey. Behaviour

110:276-293. , and S. Redston. 1987. Conspicuousness of distasteful prey affects the strength and durability

of one-trial avoidance learning. Anim. Behav. 35: 739-747.

Selden, P. A., and R. M. H. Smith. 1978. The provenance of gizzard grit from the red grouse

/Lagopus lagopus scoticus [Lath.]) of Bleaklow, Derbyshire. Naturalist 103:145-150.

SillSn-TuUberg, B. 1985. The significance of coloration per se, independent of background, for predator avoidance of aposematic prey. Anim. Behav. 33:1382-1384.

Slaby, M., and F. Slaby. 1977. Color preference and short-term learning by Steller's jays. Condor

79:384-386.

U.S. Dep. Agric. 1992. Agricultural chemical usage: 1991 field crops survey. U.S. Dep. Agric.,

Econ. Res. Serv., Washington, D.C.

U.S. Dep. Commerce. 1976. Color: universal language and dictionary of names. Nat. Bur. Stand.,

Spec. Publ. 440. 184 pp.

Wis. Agric. Exp. Stn. 1960. Soils of the north central region of the United States. Wis. Agric.

Exp. Stn. Bull., 544. 192 pp.

Zar, J. H. 1984. Biostatistical analysis, second edition. Prentice-Hall, Inc. Englewood Cliffs, N.J.

718 pp. 66

Figure Captions:

Figure 1. Use of 8 colors of grit particles, against dark and light soil backgrounds, by house sparrows and northern bobwhites. Values are means for all birds tested on each soil background.

Figure 2. Use of 8 colors of grit particles, against a dark soil background, by house sparrows and northern bobwhites fed red, yellow, or blue mash. Values are means for all birds fed mash of a particular color. 67

25- I DARK SOIL D LIGHT SOIL HOUSE SPARROW

LU O 0 tr LU Q.

RED BROWN YELLOW GREEN BLUE BLACK WHITE CLEAR

DARK SOIL II LIGHT SOIL

NORTHERN BOBWHITE

RED BROWN YELLOW GREEN BLUE BLACK WHITE CLEAR GRIT COLORS

Figure 1 68

25

111 RED FOOD 20- •YELLOW FOOD • BLUE FOOD

15- HOUSE SPARROW 10-

5-

RED BROWN YELLOW GREEN BLUE BLACK WHITE CLEAR 50-

LAI RED FOOD 40- •YELLOW FOOD • BLUE FOOD 30-

— 20 - NORTHERN BOBWHITE

10-

1 I^ Jm jaJL RED BROWN YELLOW GREEN BLUE BLACK WHITE CLEAR GRIT COLORS

Figure 2 69

CHAPTER VI. GRIT-USE PATTERNS IN NORTH AMEMCAN BIRDS: THE INFLUENCE OF BODY SIZE, DIET, AND SEX

James P. Gionfriddo and Louis B. Best

A paper to be submitted to The Wilson Bulletin

Best and Gionfriddo (1991) characterized grit use by 22 species of North American birds.

The impetus for that work was the relevance of grit use to the problem of avian mortality from the ingestion of granular pesticides used to control com rootworms and other agricultural pests. Birds included in that study therefore were limited to species that commonly use midwestem cornfields during the breeding season, when pesticides usually are applied. To determine the generality of the grit-use patterns identified in that investigation, the present research examines grit use by a larger number of avian species, over a wider geographical area, and it includes many birds that were collected during the nonbreeding season. Its objectives were to survey grit use by a broad range of avian species and to examine the influence of bird body size, diet, and sex on the amounts and characteristics of grit used by birds.

METHODS

We obtained birds opportunistically from a variety of sources including roadkills, collisions with windows, hunter harvests, and other research projects. Birds were collected year-round and from 12 (mostly midwestem) states. We removed the gizzards from all collected birds and preserved them in ethanol. Later, each gizzard was sliced in half and its contents were flushed into a petri dish and examined under a stereomicroscope. We separated all grit particles from the other gizzard contents and excluded particles < 0.1 mm in size because they were not considered to 70 be grit intentionally ingested by the birds. We then systematically counted the grit and characterized particles on the basis of size, shape, and surface texture. The longest and shortest dimensions of each particle were measured to the nearest 0.1 mm with a digital caliper or an ocular micrometer in the microscope. We used the average of these two values as a measure of particle size, and their ratio as a shape index value. Shape index values were > 1.0, with 1.0 representing a somewhat spherical shape and larger values representing more oblong shapes. We characterized the surface texture of each grit particle in 499 gizzards by using a classification system developed by petrologists to describe mineral grains (Fig. 1). The 5 surface-texture categories were angular, sub-angular, sub-rounded, rounded, and well-rounded. An overall mean surface-texture value, the surface-texture index, was calculated for each bird by assigning particles in the angular category a value of 1, those in the sub-angular category a value of 2, etc.

For comparisons of grit use based on diet, we classified each bird as an insectivore, granivore, omnivore, frugivore, or carnivore, taking into account the month in which the bird was collected and following the classification of DeGraaf et al. (1985). Ring-necked Pheasants (scientific names of avian species are given in Table 1) collected during the non-breeding season, however, were classified as granivores (rather than herbivores) because most of their non-breeding season diet consists of seeds (e.g., Dalke 1937, Ferrel et al. 1949, Korschgen 1964). Carnivores and frugivores were excluded from some analyses because of small sample sizes (see Results).

Bird body masses were obtained from Dunning (1993). For sexually dimorphic species used in intraspecific comparisons between the sexes (i.e., species with > 5 birds of each sex included in the sample), we assigned the sex-spedfic masses given by Dunning. For the other sexually dimorphic species, we assigned to each bird the mean of Dunning's values for males and females. 71

Regression analysis was used to examine the relationship between mean grit size and bird body size. We used analysis of variance (ANOVA) to examine differences in grit use among taxonomic groups and among birds consuming different t5^es of foods. When ANOVA detected differences among taxonomic or dietary groups, we used Student-Newman-Keuls (SNK) multiple comparison tests to determine specifically which groups differed. Pearson product-moment correlations were calculated to determine if mean grit size and the number of grit particles per gizzard were related. Two-tailed t-tests were used to determine if mean grit counts, sizes, shape- index values, or surface-texture values differed between the sexes. Unless otherwise indicated, a significance level of P < 0.05 was used for statistical tests.

RESULTS

Gizzard contents of birds representing 90 species and 10 orders were examined. Grit was found in gizzards of 62 species (9 orders). Frequencies of occurrence and grit counts per gizzard varied greatly among species. Low values of these variables often were associated with small sample sizes. For example, of the 41 species with mean grit counts < 4, 36 were represented by < 5 birds. Except for the diet-based comparisons (in which data from species with similar diets were combined) our analyses of grit use were limited to those species for which the contents of at least 5 gizzards were examined. This limitation was imposed because of the extreme interspecific variation in the number of grit particles per gizzard, a variable for which there exists only one

value per gizzard. (For other variables, such as grit size, shape, or surface texture, each gizzard

yielded as many values per variable as there were grit particles in the gizzard.) Among the 35

avian species for which > 5 gizzards were examined, frequencies of grit occurrence in gizzards

ranged from 0 to 100 percent, and mean grit counts per gizzard ranged from 0 to 281 (Table 1). 72

Gizzards of Ring-necked Pheasants, American Tree Sparrows, and House Sparrows had the highest frequencies of occurrence of grit, and also generally had the highest grit counts. Low frequencies of occurrence and grit counts were found in Eastern Kingbirds, Cedar Waxwings, Bam

Swallows, Dickcissels, Common Yellowthroats, Yellow-rumped Warblers, and Northern Orioles.

There was a general tendency for relatively high (or low) occurrences of grit to be associated with relatively high (or low) grit counts. Intraspedfic variation in grit counts was substantial: standard deviations typically exceeded mean values (Table 1).

Regression analysis determined that mean grit size was related to bird body size, increasing linearly with the log^^g^ of the body mass (Fig. 2). To permit examination of the

relationships between mean grit size and other variables (with the effects of bird body size

partitioned out), we adjusted the mean grit size for each species by adding the species' residual

value to the overall sample mean grit size (Steel and Torrie 1980:251). For most avian species

tested, the adjusted mean grit size and the mean grit count were not related. Among the 33 grit-

bearing species for which we examined > 5 gizzards, a significant (P < 0.001) negative correlation

was found between the adjusted mean grit size and the mean grit count in only 4 species (Ring-

necked Pheasant, Northern Bobwhite, House Sparrow, and Savannah Sparrow).

Mean grit counts per gizzard differed among birds consuming different types of food (£3^

1432 ~ 59.01, P < 0.00005). Gizzards of granivores contained more grit particles than those of

insectivores, omnivores, and frugivores (SNK test, P < 0.05) (carnivores were excluded because of

small sample size). The adjusted mean grit size, the mean shape index value, and the mean

surface texture index value did not differ among granivores, insectivores, and omnivores (size: F2,

= 2.41, P = 0.090; shape: Fj^ = 0.691, P = 0.501; surface texture: Fj^ 493 = 2.455, P = 0.087)

(carnivores and frugivores were excluded because of small sample sizes). 73

Among the 17 species for which we examined > 5 gizzards for each sex (Table 1), mean grit counts differed (P < 0.05) intraspedfically between the sexes only in Ring-necked Pheasants (P =

0.002) and Red-headed Woodpeckers (P = 0.026). In both species, gizzards of females contained more grit than those of males. Intersexual comparisons of adjusted mean grit sizes, mean shape index values, and mean surface texture index values detected few differences. In Brown-headed

Cowbirds, females used larger, less oblong, and more angular grit than males (P = 0.003,0.008, and 0.022, respectively). Female Ring-necked Pheasants and Homed Larks used smaller grit than males (P = 0.019 and 0.045, respectively). Because surface texture index values were determined only for 499 birds, sample sizes permitted intersexual comparisons within only 5 species: Northern

Bobwhite, Brown-headed Cowbird, Red-winged Blackbird, Vesper Sparrow, and House Sparrow.

DISCUSSION

Grit generally is found in the gizzards of most species that eat plant parts (Famer 1960,

Meinertzhagen 1964) and many that eat insects (e.g.. Barlow et al. 1963, Jenkinson and Mengel

1970, Barrentine 1980, Mayoh and Zach 1986). In the present study, we found grit in gizzards of

62 of 90 species (69%). Spedes with low frequencies of occurrence of grit (and low grit counts)

generally were insectivores, whereas those with high frequencies of occurrence (and high grit

counts) usually were granivores (see below). Our findings are consistent with those of numerous

studies which have shown that, among avian species that use grit, most individuals have grit in

their gizzards (e.g., Westerskov 1965, May and Braun 1973, Pinowska 1975, Hdgvar and 0stbye 1976, Hogstad 1988, Best and Gionfriddo 1991).

Grit use often varies with such factors as the age of the bird (Bartonek 1969, Verbeek 1970,

Alonso 1985, Mayoh and Zach 1986), diet (e.g., Mott et al. 1972, Norris et al. 1975, Alonso 1985, Bishton 1986), sex and reproductive status (e.g.. Harper 1964, Kopischke and Nelson 1966, May and Braun 1973, Pinowskaand Kragnicki 1985), and the characteristics (Myrberget et al. 1975, Norris et al. 1975, Gionfriddo and Best 1995) and availability (Bump et al. 1947, Tindall 1973, Norris et al. 1975) of suitable grit particles. The large amounts of grit we observed in gizzards of Ring- necked Pheasants, American Tree Sparrows, and House Sparrows are not surprising (see below) because these species feed on the ground, mainly on seeds. The relatively low grit counts and frequencies of occurrence of grit in gizzards of Eastern Kingbirds, Bam Swallows, and Cedar

Waxwings were expected (see below) because these species feed aerially or in trees, on insects or fruits. The finding that Dickcissels also used little grit on their North American breeding grounds is consistent with Zimmerman's (1963) report that wintering Dickcissels in central America used relatively large amounts of grit, but breeding birds in Illinois used very little. Zimmerman attributed the difference to the EHckdssels' heavier use of insects in North America and seeds in central America. A diet of insects gleaned in the canopies of trees or shrubs characterized the other species that tended to use little or no grit (Common Yellowthroats,Yellow-rumped Warblers,

Northern Orioles).

The observed log-linear relationship between mean grit size and bird body mass is similar to that reported for 19 avian species collected mainly in the Midwest during the breeding season

(Best and Gionfriddo 1991). Augmenting the earlier sample by including birds representing many additional avian taxa, geographical locations, and seasons did not substantially alter the linear model describing this relationship. The lack of a strong relationship between the mean grit size and the mean grit count for most (29 of 33) species we tested differs from the results of other field

(Myrberget et al. 1975, Norris et al. 1975, Alonso 1985, Best and Gionfriddo 1991) and laboratory

(McCann 1939, Smith 1960, Gionfriddo and Best 1995) studies which found that the larger the grit 75 particles, the fewer were present in gizzards. The current finding is consistent, however, with the results of one of our experiments with captive House Sparrows (Diet Experiment in Gionfriddo and

Best 1995).

Diet is a major factor influencing avian grit use. Relatively large amounts of grit often are associated with diets consisting of hard, coarse materials, especially seeds and other plant parts

(Famer 1960, Meinertzhagen 1954). Insectivores often use less grit than herbivorous or granivorous birds (Mott et al. 1972, Bishton 1986, Hogstad 1988), and frugivores typically use very little grit

(Meinertzhagen 1954,1964). The amounts of grit needed by insectivores may depend on the hardness of the prey consumed. The digestion of soft-bodied larvae, for example, may require relatively little grit, whereas the breakdown of hard-bodied insects (e.g., adult coleopterans) may require large amounts (Pinowska 1975, Gionfriddo and Best 1995). In some cases, hard insect fragments are retained in the gizzard where they serve as grit substitutes by aiding in the mechanical grinding of softer foods (Bird and Smith 1964, Jenldnson and Mengel 1970, Mott et al.

1972). Our finding no differences in mean grit size, mean grit shape, and mean grit surface texture among birds consuming different diets indicates that different foods do not require different types

(sizes, shapes, surface textures) of grit for adequate digestion. On the other hand, if birds simply consume whatever grit is available, with little discrimination in terms of these particle characteristics, then the observed similarities or dissimilarities among birds could merely reflect the relative availability of certain types of particles. The availability of grit probably plays an important role in determining the characteristics of grit particles in birds' gizzards.

Grit use by males and females often is reported to be similar (e.g., Alonso 1985, Norman and Brown 1985, Garcher and Carroll 1991, Gionfriddo and Best 1995). When differences exist, they sometimes are due to differences in body size (Rajala 1958, Pulliainen 1979, Norman and 76

Mumford 1985) or to the females' increased calcium requirements during egg laying (Sadler 1961,

Harper 1964, Taylor 1970). Females may greatly increase their consumption of grit during the egg- laying period (Pinowska and Krainicki 1985), and/or they may selectively consume caldum-rich grit particles (Harper 1964, Korschgen 1964, Kopischke and Nelson 1966). Such reproduction-related changes in grit use (and the intersexual differences that result from them) may be short-lived

(Pinowska and KraSnicki 1985), however, and therefore would not have been detectable in our study.

ACKNOWLEDGMENTS

We thank K. L. Andersen, K. K. Aulwes, B. Ballard, C. Best, J. D. Best, N. Best, J. R.

Gionfriddo, J. Grady, D. S. Huntrods, L. D. Igl, A. L. Linville, F. Winandy, and G. Zenitsky for assisting with the lab work and data tabulation. We are also grateful to those who provided or collected birds for our study, especially J. J. Dinsmore, B. J. Giesler, L. D. Igl, D. W. DeGeus, D. S.

Huntrods, and G. M. Booth. We appreciate the cooperation of various state and federal agencies in granting permission for the collection of birds. J. J. Dinsmore, E. E. Klaas, J. L. Sell, and K. C.

Shaw reviewed an earlier draft of the manuscript and offered helpful suggestions. Funding was provided by Miles, Inc., Rhone-Poulenc, American Cyanamid, and Dow Elanco.

LITERATURE CITED

Alonso, J. C. 1985. Grit in the gizzard of Spanish Sparrows (Passer hispaniolensis^. Vogelwarte

33:135-143.

Barlow, J. C., E. E. Klaas, and J. L. Lenz. 1963. Sunning of Bank and Cliff swallows. Condor

65:438-440. 77 barrentine, C. D. 1980. The ingestion of grit by nestling Bam Swallows. J. Field Omithol.

51:368-371.

Bartonek, J. C. 1969. Build-up of grit in three pochard species in Manitoba. Wilson Bull.

81:96-97.

Best, L. B., and J. P. Gionfriddo. 1991. Characterization of grit use by cornfield birds. Wilson

BuU. 103:68-82.

Bird, R. D., and L. B. Smith. 1964. The food habits of the Red-winged Blackbird, Agelaius

phoeniceus. in Manitoba. Can. Field-Nat. 78:179-186. bishton, G. 1986. The diet and foraging behaviour of the Dunnock Prunella modularis in a

hedgerow habitat. Ibis 128:526-539.

Bump, G., R. W. Darrow, F. C. Edminster, and W. F. Crissey. 1947. The Ruffed Grouse: life

history, propagation, management. N.Y. State Conserv. Dep., Albany. 915 pp.

Dalke, p. L. 1937. Food habits of adult pheasants in Michigan based on crop analysis method.

Ecology 18:199-213.

De Graaf, R. M., N. G. Tilghman, and S. H. Anderson. 1985. Foraging guilds of North

American birds. Environ. Manage. 9:493-536.

Dunning, J. B., Jr., ed. 1993. CRC handbook of avian body masses. CRC Press, Boca Raton,

Florida.

Farner, D. S. 1960. Digestion and the digestive system, p. 411-467. In A. J. Marshall [ed,].

Biology and comparative physiology of birds. Vol. 1. Academic Press, New York.

Ferrel, C. M., H. Twining, and N. B. Herkenham. 1949. Food habits of the Ring-necked

Pheasant fPhasianus colchicus^ in the Sacramento Valley, California. Calif. Fish and Game

35:51-69. 78

Garchbr, M. L., and J. P. Carroll. 1991. Comparative diet study of male and female Wilson's

Phalaropes in North Dakota. J. Pa. Acad. Sd. 64 (Suppl.):190.

Gionfrtodo, J. P., and L. b. best. 1995. Grit use by House Sparrows: effects of diet and grit size.

Condor, in press.

HAgvar, S., and E. 0stbye. 1976. Food habits of the Meadow Pipit Anthus pratensis (L.) in

alpine habitats at Hardangervidda, south Norway. Norw. J. Zool. 24:53-64.

Harper, J. A. 1964. Calcium in grit consumed by hen pheasants in east-central Illinois. J. Wildl.

Manage. 28:264-270.

Hogstad, O. 1988. Foraging pattern and prey selection of breeding Bramblings Fringilla

montifringilla. Fauna Norv. Ser. C, Cinclus 11:27-39. jenkinson, M. A., and R. M. Mengel. 1970. Ingestion of stones by goatsuckers (Caprimulgidae).

Condor 72:236-237.

Kopischke, E. D., and M. M. Nelson. 1966. Grit availability and pheasant densities in

Minnesota and North Dakota. J. Wildl. Manage. 30:269-275.

Korscmgen, L. J. 1964. Foods and nutrition of Missouri and midwestem pheasants. Trans. N.

Am. Wildl. Nat. Resour. Conf. 29:159-180.

May, T. a., and C. E. Braun. 1973. Gizzard stones in adult White-tailed Ptarmigan (Lagopus

leucuru9'> in Colorado. Arctic Alpine Res. 5:49-57.

Mayoh, K. R., and R. Zach. 1986. Grit ingestion by nestling Tree Swallows and House Wrens.

Can. J. Zool. 64:2090-2093.

McCann, L. J. 1939. Studies of the grit requirements of certain upland game birds. J. Wildl.

Manage. 3:31-41.

Meinertzhagen, R. 1954. Grit. Bull, Br. Omithol. Club 74:97-102. Meinertzhagen, R. 1964. Grit, p. 341-342. In A. L. Thomson [ed.], A new dictionary of birds.

McGraw-Hill, New York, New York.

MOTT, D. F., R. R. West, J. W. De GRAZIO, AND J. L. GUARDING. 1972. Foods of the Red-winged

Blackbird in Brown County, South Dakota. J. Wildl. Manage. 36:983-987.

Myrberget, S., C. NORRIS, and E. NORRIS. 1975. Grit in Norwegian Lagopus spp. Norw. J,

Zool. 23:205-212.

Norman, F. I., and R. S. brown. 1985. Gizzard grit in some Australian waterfowl. Wildfowl

36:77-80.

Norman, F. I. and L. MUMFORD. 1985. Studies on the Purple Swamphen, Porphyrio porphyrio.

in Victoria. Aust. Wildl. Res. 12:263-278. norris, E., C. norris, and J. B. Steen. 1975. Regulation and grinding ability of grit in the

gizzard of Norwegian Willow Ptarmigan (Lagopus lagopus). Poult. Sd. 54:1839-1843.

PiNOWSKA, B. 1975. Food of female House Sparrows (Passer domesticus L.) in relation to stages of

the breeding cycle. Pol. Ecol. Stud. 1:211-225.

PiNOWSKA, B., and K. Krasnicki. 1985. Quantity of gastroliths and magnesium and calcium

contents in the body of female House Sparrows during their egg-laying period. Zesz.

Nauk. Filii UW, 48, Biol. 10:125-130. pulliainen, E. 1979. Grit intake of the Capercaillie, Tetrao urogallus. in the northern Finnish

taiga in autumn. Aquilo Ser. Zool. 19:45-47.

Rajala, p. 1958. (The choice of grinding stones by Capercaillie, Black Grouse, and ptarmigan in

the light of enclosure experiments.) Suomen Riista 12:89-93.

Sadler, K.C. 1961. Grit selectivity by the female pheasant during egg production. J. Wildl.

Manage. 25:339-341. 80

Smith, R. E. 1960. The influence of size and surface condition of grit upon the digestibility of feed

by the domestic fowl. Can. J. Anim. Sd. 40:51-56.

Steel, R. G. D., and J. H. Torrie. 1980. Prindples and procedures of statistics: a biometrical

approach, 2nd ed. McGraw-Hill Book Co., New York, New York.

Taylor, T. G. 1970. The provision of caldum and carbonate for laying hens, p. 108-117. In H.

Swan and D. Lewis [eds.], Proc. Univ. Nottingham Fourth Nutrition Conf. for Feed

Manufacturers. J. and A. Churchill, London. tindall, A. R. 1973. Gastroliths in Norwegian Grouse (Lagopus lagopus). Acta Physiol. Scand.,

Suppl. 396:66.

Verbeek, N. A. M. 1970. Breeding ecology of the Water Pipit. Auk 87:425-451.

Westerskov, K. 1965. Utilisation of grit by pheasants in New Zealand. New Zealand Dep.

Internal Affairs Wildl. Publ. No. 65. 31 pp.

Zimmerman, J. L. 1963. The bioenergetics of the Dickdssel, Spiza americana. Ph.D. dissertation,

Univ. ni., Urbana. 142 pp. Table 1. Summary of grit use by wild birds.®

Occur­ Count*^ Mean Gizzards rence Mean Median size Shape Surface Spedes sampled (%)^ (±SD) (mm) index*^ texture*^'®

Ring-necked Pheasant (Phasianus colchicus') 41^ 100 173+206 89 2.3 2.0 3.3

Northern Bobwhite fColinus virginianus^ 75^ 90 49±106 12 1.8 1.8 3.1

Killdeer fCharadrius vodferus) 28^ 93 8±9 5 1.9 2.1 2.6

Rock Dove fColumba livia't 15 100 69+43 60 2.3 2.0 3.3

Mourning Dove fZenaidura macroura) 40 68 10±16 3 2.1 1.7 3.0

Yellow-billed Cuckoo fCoccyzus americanus) 9 44 3±6 0 1.6 1.8 3.0

Red-headed Woodpecker (Melanerpes erythrocephalus) 27^ 57 31±59 2 0.9 1.8 3.0

Eastern Kingbird fTyrannus tyrannus^ 29^ 24 1±4 0 1.3 1.9 2.7

Bam Swallow flHirundo rustical 23 22 1+4 0 1.2 3.1

Homed Lark (Eremophila alpestris^ 69^ 99 11+13 8 1.2 1.7 3.0

Blue Jay CCyanodtta cristata^ 20^ 85 35±42 15 1.6 2.1 2.8

American Crow rCorvus brachyrhynchos') 64^ 53 49±156 2 2.9 1.7 3.1 Cedar Waxwing (Bombydlla cedorum) 20 9±40 0 0.3 1.7 2.9

Hermit Thrush fCatharus guttatus^ 89 52+101 17 0.3 1.8 2.8

American Robin fTurdus migratorius) 44 12+26 0 0.8 2.3 2.7

European Starling fStumus vulgaris) 36 21+85 0 1.0 1.8 2.7

House Wren rTroglodytes aedon) 57 3±5 1 0.3 1.7 3.0

House Sparrow (Passer domesticus) 98 281+476 97 0.7 1.9 2.9

Yellow-rumped Warbler fPendroica coronata) 0 0 0

Common YellowthroatfGeotMypis trichas) 21 1+2 0 0.3 1.8 2.8

Fox Sparrow fPasserella iliaca) 100 102±88 93 0.5 2.0 3.1

Song Sparrow fMelospiza melodia) 93 14±15 8 0.8 1.8 2.9

Savannah Sparrow fPasserculus sandwichensis) 92 43±96 21 1.0 2.0 3.1

American Tree Sparrow (Spizella arborea) 100 267+212 203 0.4 1.9 3.1

Chipping Sparrow fSpizella passerina) 95 12+16 7 0.9 2.1 2.9

Vesper Sparrow fPooecetes gramineus) 86 12+14 8 0.9 1.8 3.1

T^rk Sparrow fChondestes grammacus) 100 42+50 22 0.6 1.8 3.2

EKckdssel fSpiza americana) 25 4±18 0 0.8 2.0 3.2 Northern Cardinal fCardinalis cardinalis^ 22' 73 40±82 6 1.0 2.6 2.9

Indigo Bunting fPasserina cyaneal 21 81 35+91 4 0.9 1.8 2.8

Northern Oriole (Icterus galbulal 5 0 0 0

Red-winged Blackbird fAgelaius phoeniceus^ 82^ 73 17+61 4 1.1 1.8 3.0

Western Meadowlark fStumella neglectal 9 44 2±3 0 1.4 1.8 3.0

Common Crackle fOuiscalus quiscula^ 47' 57 10±21 1 0.9 2.2 2.9

Brown-headed Cowbird (Molothrus atert 175' 52 10±30 1 1.0 2.0 2.9

® Includes oidy those species for which > 5 gizzards were sampled. ^ The percentage of gizzards in which grit particles were found. The mean and median numbers of grit particles found per gizzard. The overall mean shape-index and surface-texture-indexvalues. See text for a description of how these values were derived. ® This variable was called "roundness" in Best and Gionfriddo 1991. ' These 17 species were used for intraspedfic, intersexual comparisons of grit use. 84

Figure Captions:

Figure 1. Five categories used to characterize grit surface texture.

Figure 2. Relationship between mean grit size and mean bird body mass. Body masses were obtained from Dunning (1993). Each dot represents a species for which the contents of at least 5 gizzards were examined. 85

Angular $gt?-angglar Sharp and irregular Corners slightly rounded corners and inlets sharp

Sub-rounded Rounded Well-rounded Corners rounded and inlets Corners well-rounded and Smoothly rounded with more or less smooth only a few inlets no corners or inlets

Figure 1 86

4.0

y = -0.768 + 1.112 Log(x) / - R' = 0.666 3.0 E o 0 N o / o CO o / 2.0 o / 0 0 o / 0 \ C 0 (0 o 0) 1.0 0^ % °

? ^ 0.0 T ^ 10 100 1,000 10,000 Mean Body Size (g)

Figure 2 87

CHAPTER Vn. A REVffiW OF GRTT USE BY BIRDS

A paper to be submitted to Current Ornithology

James P. Gionfriddo and Louis B. Best

INTRODUCTION

The importance of grit in avian digestion has been recognized for at least two centuries

(Spallanzani 1783 [dted in Westerskov 1965]). The gizzards of most birds that eat plant parts

(Famer 1960, Meinertzhagen 1964) and many that eat invertebrates (e.g.. Barlow et al. 1963,

Jenkinson and Mengel 1970, Peterson and Ellarson 1977, Barrentine 1980, Mayoh and Zach 1986) contain grit. Many studies have shown that, among avian species that use grit, most individuals have grit in their gizzards (e.g., Cottam 1929, Ferrel et al. 1949, West 1967, Mott et al. 1972, Tuck

1972, Pinowska 1975, H&gvar and 0stbye 1976, Wiley and Wiley 1979, Koubek 1986, Hogstad 1988,

Moksnes 1988, Best and Gionfriddo 1991a).

As the benefits of grit use became more widely known, the practice of providing grit to birds became increasingly widespread. Feeding grit to poultry is generally considered a wise economic practice (Brook 1957, Smith and Maclntyre 1959, Smith 1960, Mcintosh et al. 1962).

Management of British upland game birds has long included supplementing natural grit supplies by providing suitable grit at carefully selected sites (Smith and Rastall 1911, Anonymous 1937,

Seldon and Smith 1978). Wildlife professionals in the United States have recommended that winter feeding programs for birds include the supplying of grit (Gordon 1925, Hicks 1940, Fox 1941 [all dted in Robel and Bisset 1979]; Leopold 1933:277; Davis et al. 1961), and grit is provided at some national wildlife refuges and other wildlife management areas (Mcllhenny 1932, Sharp and

McClure 1945, Chabreck et al. 1989). 88

Several authors have contended that some birds require grit for digestion and would weaken and die if deprived of it (e.g., Anonymous 1937, Vessey-Fitzgerald 1946:16, Meinertzhagen

1954, Short 1993:35). Smith and Rastall (1911) stated that grit is essential for the digestion of hard grain or seeds by gallinaceous birds. Westerskov (1965) identified several lines of evidence to support his contention that grit is an indispensable component in the gizzards of Ring-necked

Pheasants (scientific names of avian species are listed in Appendix 2) in New Zealand: (1) Even in areas where grit supplies were limited, pheasants had grit in their gizzards throughout the year.

(2) Pheasants raised in captivity and then released into the wild were later found to have as much grit in their gizzards as wild pheasants. (3) Pheasants began consuming grit soon after hatching and continued throughout their lives.

Although grit use may be highly beneficial to birds, it does not seem to be essential to the survival of birds receiving adequate nutrition. Studies of poultry have shown, for example, that although grit use hastens and improves digestion, it is not essential to survival, growth, or egg production (Buckner and Martin 1922, Buckner et al. 1926, Fritz 1937). Moreover, birds whose gizzards have been removed may live indefinitely (Burrows 1936), although they may show a reduced ability to digest coarse foods (Fritz et al. 1936). Nestler et al. (1946) concluded that grit is not essential to growth, welfare, or reproduction of northern bobwhites, based upon his studies of captive birds deprived of grit throughout life.

In some instances birds may make very regular visits to specific locations to acquire grit.

Meinertzhagen (1954) observed a flock of Eurasian Siskins in Ireland that visited a gravel path each morning for 5 days to collect grit. He also observed regularity in grit use by at least 5 other avian species at sites in Europe and Asia. Westerskov (1965) reported that Ring-necked Pheasants regularly visited New Zealand roadsides in the mornings and evenings to consume grit. Red 89

Grouse on moorland in the British Isles made regular trips to low-lying areas to obtain grit (Selden and Smith 1978). Verbeek (1971) described regular, hourly visits made by a female Anna's

Hummingbird to a specific rock where it seemed to consume sand. Noting that this behavior occurred both during (May) and after (July) the species' breeding season, Verbeek speculated that the hourly periodicity of the July observations may have reflected the rate of absorption of calcium from the sand and associated fluctuations in blood calcium levels as the bird's medullary bone calcium reserves were replenished.

For game birds, spatial and temporal regularity in grit seeking often concentrates hunting pressure at grit collection sites. For example. Spruce Grouse in Alaska and western Canada commonly visit gravelled roads to consume grit, and most (90% in Alaska) hunter-killed grouse are killed along such roads (Lumsden and Weeden 1963, Ellison 1974). March and Sadleir (1972) described a coastal grit collection site used by Band-tailed Pigeons in British Columbia. Grit was washed out onto the mud flats of a tidal bay where it was gradually exposed as the tide receded.

Pigeons perched in shoreline conifers and made short, brief flights to the mud flats for grit. Grit collection sites are the most heavily-hunted Band-tailed Pigeon areas in British Columbia (March and Sadleir 1970). McDhenny (1932) described a small, sandy beach in southwest Louisiana that attracted wintering Snow Geese daily from many kilometers away because of the general lack of suitable grit in the region. Snow Geese were hunted there by American aboriginals and later by market hunters and sportsmen. McDhenny speculated that more Snow Geese had been killed at that site than at any other in the United States.

Grit in birds' gizzards sometimes provides useful information regarding avian migratory movements. Meinertzhagen (1954,1964) and Gudmundsson (1972) described several instances in which gizzards contained grit only available at specific, extracontinental locations. For example. 90 many migratory species that breed in Iceland stop temporarily in the British Isles en route to wintering sites in Africa and elsewhere (Gudmundsson 1972). This was confirmed when black lava particles only available in Iceland were found in gizzards of swans and geese shot in Scotland

(Meinertzhagen 1954). Examination of gizzard grit also has been used to determine if birds in a partially migratory population were year-round residents or seasonal visitors (Gudmundsson 1972).

The evolutionary origin(s) of avian grit use is (are) obscure. Stomach stones were used by at least two groups of Cretaceous reptiles, including sauropod dinosaurs and aquatic plesiosaurs

(Darby and Ojakangas 1980, Stokes 1987). Moas and other Pleistocene birds in New Zealand

(Forbes 1892, Young 1967), and Pleistocene, Holocene, and Recent birds in Alaska (Hoskin et al.

1970) also carried stones in their stomachs. The gizzard-like stomachs of modem crocodilians

(Darby and Ojakangas 1980, Siegel-Causey 1990) often contain stones. For dinosaurs and crocodilians, the relative importance of stomach stones as ballast versus grinding agents is

uncertain. Siegel-Causey (1990) suggested that stomach stones first were used by reptiles because

of their value as ballast, and later their use was retained in avian basal groups because of the

(previously secondary) digestive benefits.

Avian grit use has been studied mainly in three groups of birds: poultry, wild gallinaceous

birds, and waterfowl. Poultry grit research has been motivated by the increases in growth rates,

egg production, food digestibility, and feeding efficiency associated with grit use (refs. cited in

Mcintosh et al. 1962). Interest in grit use by gallinaceous species and waterfowl stems from their

value as game birds. Much of the research on gallinaceous birds, especially the Ring-necked

Pheasant, has focused on the possible roles of grit availability and use in limiting population

densities and geographical distributions through effects on reproduction (especially eggshell

production) (e.g., McCann 1939,1961; Dale 1954,1955; Dale and DeWitt 1958; Harper 1963,1964; 91

Harper and Labisky 1964; Korschgen 1964; Korschgen et al. 1965; Kopischke 1966; Kopischke and

Nelson 1966; Vance 1971). The focus of most waterfowl grit-use research has been on the relevance of grit use to the problem of lead poisoning (e.g., Godin 1967, Trost 1981, Hall and Fisher

1985, Spray and Milne 1988) or on the determination of waterfowl grit requirements (e.g., Thomas et al. 1977, Halse 1983, Skead and Mitchell 1983, Norman and Brown 1985). Recently, interest in avian grit use also has been prompted by a desire to reduce avian mortalities associated with the use of granular pesticides, which may be consumed by birds as grit (e.g.. Best and Gionfriddo

1991a; Best 1992; Best and Fischer 1992; Gionfriddo and Best, unpubl. data). This chapter reviews, from an ecological perspective, the information available on avian grit use, drawing on the literatures of avian biology, wildlife management, and poultry science.

FUNCTIONS OF GRTT USE

Several functions have been ascribed to grit use by birds, relating to improved digestion of food and dietary mineral supplementation. Perhaps the most commonly proposed function of grit

use is the facilitation of mechanical grinding and pulverization of food in the gizzard

(Meinertzhagen 1964, Ziswiler and Famer 1972). In many avian species (most omnivores,

insectivores, herbivores, and granivores), the gizzard is a specialized, highly muscular organ. The

tough, coarse foods these birds often consume require mechanical breakdown to facilitate the

activity of digestive enzymes (McLelland 1979). Powerful muscular contractions of the gizzard

crush and grind food items against the dorsal and ventral grinding plates (greatly thickened

portions of the cuticle that lines the inner surface of the gizzard). The presence of grit particles in

the gizzard is thought to improve the efficiency of this process by providing hard, moving,

grinding surfaces within the food matrix. 92

Grit use as a grinding aid seems to be related to diet, being most common among birds consuming coarse, hard plant or animal parts (McLelland 1979). Most granivores and other herbivorous birds use grit (Meinertzhagen 1954,1964; Famer 1960), as do many wholly insectivorous birds (e.g., Jones 1933, Harrisson 1954, Barlow et al. 1963, Jenkinson and Mengel

1970, Brown 1976, Barrentine 1980, Mayoh and Zach 1986), evidently to facilitate the mechanical breakdown of food. Seasonal changes in the diets of birds may affect patterns of grit use. Hogstad

(1988) reported that grit use by Bramblings was much greater when they consumed seeds than when they shifted to soft insect larvae during the breeding season. As Dunnocks changed their diet in late summer from insects to seeds and insects, their grit use increased significantly (Bishton

1986). These and other examples suggest that, at least for some species, the value of grit lies in its role in aiding digestion by grinding and crushing hard food items. Seasonal changes in the mean size of grit used by birds also are correlated with shifts in diet. There is often a greater use of larger grit particles during those seasons in which hard, difficult-to-digest food items are consumed (May and Braun 1973, Alonso 1985) (see Characteristics of Grit ~ Grit Size). Poultry experiments also have demonstrated that the value of insoluble grit as a grinding agent varies with the consistency of the diet. Feeding insoluble grit usually improved the digestibUity of coarse foods

(Titus 1949, Scott and Heuser 1957, Smith 1960, Oluyemi et al. 1978, Rowland and Hooge 1980), but sometimes had no detectable influence on the digestibility of finer or softer foods (Walter and

Aitken 1961, Proudfoot 1973, Sibbald and Gowe 1977). Experiments that directly compared birds fed coarse versus fine diets generally found that the use of insoluble grit provided greater benefits when coarse foods were eaten (Fritz 1937, Balloun and Phillips 1956, Smith and Maclntyre 1959,

Mcintosh et al. 1962). For further discussion of the value of grit use in the digestion of coarse, hard foods, see Amount Used. 93

A second function commonly attributed to grit use is the supplementation of minerals, espedally caldum, in the diet (e.g., McCann 1961, Harper 1963, Korschgen 1964, Norris et al. 1975,

Turner 1982, Campbell and Leatherland 1983). Caldum is a critical nutrient for birds, espedally during the period of rapid growth of the young and during the reproductive season for females

(Harper 1963). Recent studies suggest that caldum may be a limiting factor in the diets of birds breeding in or near anthropogenically-addified habitats (St. Louis and Breebaart 1991 and refs. therein). Birds that feed predominantly on plant materials or other caldum-deficient foods (Fisher

1972) are espedally dependent on grit as a source of caldum (McCann 1939,1961). The diet of

Ring-necked Pheasants, for example, probably supplies only 10% of the caldum needs of reproductive females; the balance must come from calcareous grit and other sources (Harper and

Labisky 1964). For pheasants, caldum-rich grit may be an ecological factor of critical importance, sometimes even more important than climate, cover, or any single organic food type (McCann

1%1).

Some birds with high caldum requirements preferentially select limestone or other calcareous grit. Several studies have shown that calcareous grit is selected by female birds during egg laying (Sadler 1961, Harper 1964, Korschgen 1964, Kopischke 1966, Kopischke and Nelson

1966). Captive Ring-necked Pheasant hens maintained on a low-calcium diet chose limestone grit over granitic grit during egg lapng (Sadler 1961). In the midwestem United States, Korschgen

(1964) found that wild pheasant hens consumed 33 times as much (by weight) caldum-containing grit as males in April. Wild pheasant hens in Illinois not only selected calcareous rather than noncalcareous grit, but they selectively ingested limestone espedally rich in caldum (Harper 1964),

The use of calcareous grit as an exogenous source of caldum for egg formation also has been documented in female Bam Swallows and Sand Martins (Bank Swallows) (Turner 1982), Band- 94 tailed Pigeons (March and Sadleir 1972), Lesser Snow Geese (Campbell and Leatherland 1983), and

Red-billed Queleas (Jones 1976). Female House Sparrows increased their grit consumption during the egg-laying period to meet increased calcium requirements (Pinowska and Krainidd 1985). Young birds also require large amounts of calcium for rapid growth. Harper (1963) reported that free-ranging, juvenile Ring-necked Pheasants in east-central Illinois showed a definite ability to select caldtic limestone over dolomitic (relatively caldum-poor) limestone. Although the two grit types were equally available in fields and along gravel roads, the birds consumed 20 times more

(by weight) caldtic limestone.

The tendency to selectively consume caldum-rich items to meet minimum caldum requirements ("caldum appetite") also has been demonstrated in domestic fowl (Meyer et al. 1970,

Mongin and Sauveur 1974, Classen and Scott 1982) and appears to be a specific, learned preference

(Wood-Gush and Kare 1966, Hughes and Wood-Gush 1971). Joshua and Mueller (1979) maintained chickens on a caldum-deficientdiet supplemented with granular caldum carbonate, and then shifted the birds to a diet providing adequate caldum. The chickens' intake of caldum carbonate sharply decreased within a day. Lobaugh et al. (1981) found that infusion of small amounts of caldum into the carotid artery reduced chickens' consumption of caldum supplement within 150 minutes. They conduded that caldum appetite is inhibited by increased concentrations of ionic caldum in the blood, and that changes in caldum appetite occur rapidly enough to enable it to play a role in regulating caldum levels in birds. Observations of laying hens indicated that these birds were able to control their intake of food and caldum independendy, and suggested that caldum intake was regulated on an hour-to-hour basis during the egg-lajring period (Hughes 1972,

Mongin and Sauveur 1974, Nys et al. 1976). 95

In some regions of the United States, a deficiency of soil calcium may play a key role in limiting the distributions and population densities of several gallinaceous species, including

Ring-necked Pheasants (e.g., Gerstell 1937, Dale 1954, McCann 1%1), Gray Partridge (Wilson 1959), and Wild Turkeys (Allen 1962:20). The natural diet of these species is caldum-deficient, and supplementary calcium may be required for adequate reproduction (Dale 1955). Captive pheasants successfully reproduced when given caldum-rich limestone grit as a dietary supplement, but failed to ovulate more than a very few eggs when given granitic grit. Leopold (1931:125-127) first suggested that the success of Ring-necked Pheasant and Gray Partridge populations in the north- central states seemed to coincide with the area once covered by the Wisconsinan glacier.

Information on pheasant distribution and densities often supports Leopold's hypothesis (e.g.,

Gerstell 1937, Dale 1955, Harper and Labisky 1964). Soils deposited by the Wisconsinan are now known to be richer in calcium than those left by earlier gladations (Anderson and Stewart 1969).

However, geographical areas undisturbed by the Wisconsinan and other gladers also may have adequate soil caldum levels to support dense populations of Ring-necked Pheasants (e.g.,

Korschgen 1964). Moreover, the ability of pheasants to selectively consume caldum-rich grit may mean that even areas relatively low in availabile calcareous material may provide enough caldum to support pheasants (Harper and Labisky 1964, Kopischke and Nelson 1966). The relationship between soil caldum and avian distributions and densities is greatly complicated by the effects of other inorganic ions that also are spatially variable in abundance and chemical form (Anderson and

Stewart 1969,1973).

Several other possible functions of avian grit use have been proposed. The presence of grit in the gizzard may enhance digestion by further stimulating the secretion of digestive fluids

(Mdntosh et al. 1962) or by facilitating the action of such fluids (Tortuero and Centeno 1973). It 96 also may help by stirring and mixing the digestive enzymes and food particles in the digestive tract

(Tortuero and Centeno 1973, Oluyemi et al. 1978) or by slowing the rate of food passage (Mcintosh et al. 1962). Finally, grit may be ingested as a source of trace elements needed by birds (Walton

1984). To our knowledge these ideas have not been tested.

Several researchers have reported that grit use causes changes in the condition of the digestive organs. Tagami and Kuchii (1971) stated that grit use may have favorable physical or physiological effects on intestinal tract tissue. Gizzards of domestic chicks fed grit are often larger and heavier than those of chicks deprived of grit (Heuser and Norris 1946, Brook 1957, Elliott and

Hinners 1969, Tagami et al. 1969, Yamantani and Otani 1969). Grit use is probably not necessary for proper gizzard condition, however. Nestler (1946) found no gizzard abnormalities among penned Northern Bobwhites raised completely without grit.

CHARACTERISTICS OF GRIT

Among the characteristics of grit that seem to influence its use by birds are particle size, shape/surface texture, color, and composition. These grit characteristics may influence 3 components of the grit-use process: particle selection by the bird, particle retention in the gizzard, and particle alteration (physical and chemical) in the gizzard. The extent to which each grit characteristic affects grit use may vary with the bird's age, diet, sex, reproductive status, and other factors. Sources of information on characteristics of grit used by wild birds are presented in

Appendix 1.

Grit Size

Grit size varies gready, both within and among avian species, ranging from particles less than 0.1 mm in diameter (Hoskin et al. 1970, Siegfried 1973) to stones that measure more than 2.5 cm aaoss, used by large birds such as Ostriches (Meinertzhagen 1964). In general, grit size is 97 positively correlated with body size (Smith and Rastall 1911, Li^eld 1983). Among 19 avian species that use midwestem cornfields, mean grit size increased linearly with the log^^Q^ of the body mass

(Best and Gionfriddo 1991a). A similar relationship was determined from a much larger sample of

34 species of North American birds (Gionfriddo and Best, unpubl. data). Grit used by nestlings and juveniles often is smaller than that used by adults of the same species (Smith and Rastall 1911,

Siegfried 1973, Myrberget et al. 1975, Halse 1983).

The distributions of grit sizes used by various avian species differ greatly (Best and

Gionfriddo 1991a). Some species use only a narrow range of particle sizes (Anonymous 1937, Best and Gionfriddo 1991a), and supplemental grit provided by wildlife managers may be ignored if it is not the proper size (Selden and Smith 1978). Other species use a broader range of grit sizes (e.g.,

Dalke 1938, Bump et al. 1947, Anderson 1959, Lewin and Lewin 1984), some with bimodal size preferences (Best and Gionfriddo 1991a).

Grit size also is related to diet. For a given bird body size, the consumption of harder and coarser foods generally is associated with the use of larger grit (Meinertzhagen 1964, Hoskin et al.

1970, May and Braun 1973, Norris et al. 1975, Thomas et al. 1977). Larger grit particles may increase the gizzard's efficiency in mechanically breaking down hard, coarse foods. Food particle size also may influence the size of grit used. Alonso (1985) found that all three age-classes

(nestlings, juveniles, adults) of Spanish Sparrows showed a positive correlation between mean size of food particles ingested and mean size of grit used. Spanish Sparrow parents fed their nestlings increasingly large grit as the young grew and were given larger food items. A similar correlation

between food item size and grit particle size was found in several waterfowl species (Thomas et al.

1977, Nystrom et al. 1991). Because birds' diets may vary seasonally with the availability of various food sources and with changing nutritional needs, the sizes of grit in gizzards of some species also 98 may vary seasonally. For example. White-tailed Ptarmigans in Colorado (May and Braun 1973) and

Spanish Sparrows (Alonso 1985) exhibited seasonal changes in mean grit size that were correlated with seasonal dietary shifts.

Seasonal changes in grit availability, such as those caused by snow cover, also affect the size of grit in birds' gizzards (Norris et al. 1975). In general, sex and reproductive status do not seem to influence grit size use (May and Braun 1973, Trost 1981, Halse 1983, Gionfriddo and Best

1995). Although males in some populations use slightly larger grit particles than females, male body size is larger in these species (e.g., Rajala 1958, Pulliainen 1979, Norman and Mumford 1985).

In some avian species, the amount of grit in the gizzard is inversely related to grit size.

Field studies have shown that, for these species, the larger the size of the grit particles, the fewer are present in the gizzard (Myrberget et al. 1975, Norris et al. 1975, Alonso 1985, Best and

Gionfriddo 1991a, Gionfriddo and Best 1995). This relationship also has been demonstrated in captive House Sparrows (Gionliiddo and Best 1995) and Ring-necked Pheasants (McCann 1939), and in domestic chicks (Smith 1960).

Grit Shape

Little information is available regarding avian use of grit particles of various shapes (see

Appendix 1). There is some evidence that rough, angular grit is selectively consumed by birds

(Best and Gionfriddo 1994), and that grit retained in the gizzard becomes more rounded over time

(Buckner et al. 1926). Retention of grit in the gizzard also may vary with particle shape (see

Retention Time). In many instances, the use of grit particles of various shapes may largely be a

function of their availability.

Gizzards of free-ranging birds often contain grit particles of many shapes, from angular to

well rounded (Smith and Rastall 1911, Moksnes 1988, Best and Gionfriddo 1991a). It is usually not 99 possible to determine how much rounding of grit particles occurs in the gizzard (but see Hoskin et al. 1970, Selden and Smith 1978). Hoskin et al. (1970) reported that Alaskan Rock Ptarmigan grit was more angular and dull-surfaced in summer, when grit sources were always available, and more rounded and polished in winter, when fresh grit was unavailable due to snow cover. They concluded that grit availability determined retention rates and thereby influenced the shape of gizzard grit. Myrberget et al. (1975) found similar seasonal patterns in Willow Ptarmigan and Rock

Ptarmigans in Norway, and reached the same conclusion. Grit from White-tailed Ptarmigan gizzards in Colorado, however, did not change seasonally in roundness, suggesting that grit was available, consumed, and eliminated steadily year-round (May and Braun 1973).

Some temporal differences in grit shapes used may be related to diet. For example, grit in gizzards of free-ranging Iowa House Sparrows captured during the months of relatively heavy insect (mostly hard-bodied coleopterans) consumption was more angular than grit in gizzards of birds collected at other times of year, despite year-round grit availability (Gionfriddo and Best

1995).

Grit Color

Grit color is seldom mentioned in published reports of avian grit use (see Appendix 1). In his review of grit use by birds, Meinertzhagen (1964) stated that brightly colored grit is generally preferred to dull, but he offered no empirical support for this contention. Available evidence suggests that local bird populations use grit of many colors, but sometimes they favor a certain color or group of colors. For example. Red Grouse in England mainly used opaque, white quartz with traces of red (iron) stain, plus a few clear, polished quartz particles (Selden and Smith 1978).

Barrentine (1970) determined that 70% of the particles in the gizzards of nestling Bam Swallows were light colored, 10% were transparent, and 20% were dark. The color of grit used by English 100 waterfowl also varied: smaller particles were usually transparent, whereas larger ones were white, orange or brown (Thomas et al. 1977). Availability may play a major role in determining the color of grit used by birds.

The conspicuousnessof grit particles may be an important factor determining if birds notice and consume grit. Color may influence particle conspicuousness in 2 ways: (1) some colors may be inherently conspicuous to birds regardless of context (Sill§n-Tullberg 1985, Roper and Cook 1989, Roper 1990), but (2) conspicuousness also may depend on the degree of contrast with the background (Gittleman and Harvey 1980, Gendron 1986). In aviary experiments with House

Sparrows and Northern Bobwhites, Gionfriddo and Best (unpubl. data) found only a limited influence of soil background color on the selection of colored grit, and only in House Sparrows.

Pank (1976) tested the effects of seed-coloring agents and background color on Douglas fir

(Pseudotsuga menziesii^ seed acceptance by 3 species of granivorous birds and concluded that background color did not affect colored seed selection. On the other hand, grain consumption rates of captive Mourning Doves varied with the color of the background material, indicating that at least some avian feeding responses are affected by background color (Goforth and Baskett 1971).

Additional research is needed to clarify the influence of background color on avian color preferences.

Gionfriddo and Best (unpubl. data) examined colored grit use by captive House Sparrows and Northern Bobwhites by offering birds a grit mixture consisting of equal amounts of 8 colors

(red, brown, yellow, green, blue, black, white, clear) on a soil surface. In gizzards of both House

Sparrows and Northern Bobwhite, yellow, green, and white particles represented the greatest proportions of colored grit. Black and blue grit were generally used very little by the 2 avian species. The influence of food color on grit color selection then was examined by repeating the 101 experiments by using birds maintained on food dyed to match 3 of the 8 grit colors (red, yellow, blue). Regardless of food color. House Sparrows preferred brown, yellow, and white grit, and

Northern Bobwhites preferred yellow and green grit. Black and blue grit again received little use by both species. Food color affected grit color selection in both species, but was not associated with major differences in the preference rankings of the 8 grit colors. Grit color use by males and females did not differ in either species in any of the experiments. Despite the emergence of consistent overall color preference patterns among the birds, there was great variation in the responses of individual birds. Nearly all (941 of 947) birds expressed color preferences, but in many instances these preferences differed greatly from the overall patterns (Gionfriddo and Best, unpubl. data).

Experimental efforts to identify avian color preferences often have focused on responses of birds presented with a choice of colored, illuminated keys (or colored chips) in a test box, or on

responses of free-ranging birds to artificially colored food. In studies of the first type, domestic

chicks have shown preferences in the red-orange and blue-violet regions of the visible spectrum

(e.g., Hess 1956, Fischer et al. 1975, Fischer and Davis 1981); Japanese Quail generally have

preferred green and yellow, and avoided red and blue (Kovach 1974, Duecker and Schulze 1977).

The latter pattern is consistent with the selection of colored grit by captive Northern Bobwhites

(Gionfriddo and Best, unpubl. data). Much of the research examining avian food color preferences

has been prompted by a desire to reduce avian depredation of grain crops or to reduce avian

consumption of toxic baits intended for rodents. Preferred food colors varied greatly but a

consistent finding of studies in which artificially colored grain or other seeds were offered to free-

ranging birds was an avoidance of green, blue, and black items (Kalmbach and Welch 1946, Pank

1976, Slaby and Slaby 1977, Brunner and Coman 1983, Roper 1990). This result is consistent with 102 the observed avoidance of blue and black grit by House Sparrows and Northern Bobwhites

(Gionfriddo and Best, unpubl. data).

Grit Composition

The value of grit as a grinding agent and nutritional supplement greatly depends upon its mineral composition, which determines grit hardness, solubility in the avian digestive tract, and nutritional value. For this reason the composition of grit particles is sometimes a major determinant of avian use.

Most studies have found mainly quartz grit in the gizzards of wild birds (Table 1). Quartz is a very hard, relatively insoluble material that retains its angularity until completely ground to a powder, whereas softer grit particles become rounded or even polished (Meinertzhagen 1954). A preponderance of quartz in the gizzard may reflect a preference for this mineral or it may simply result from the hardness and relative insolubility of quartz, compared with other grit types such as limestone, in the ad ^lic environment of the avian digestive tract (Myrbergetet al. 1975).

Availability also may play a major role. Although quartz was quite scarce in some of the locations studied (e.g.. Smith and Rastall 1911), it was relatively abundant in most areas (Table 1).

Moreover, because birds are highly mobile, their gizzards may contain grit of nonlocal and sometimes even extracontinental origin (Meinertzhagen 1954, Gudmundsson 1972). Because of its hardness, quartz might be expected to be more efficient than limestone as a grinding agent in the gizzard. In experiments with chickens, however, both limestone and quartz achieved the same beneficial effect (improved digestion of feed) while they remained intact in the gizzard (Smith and

Maclntyre 1959). For a discussion of avian use of limestone and other calcareous grit, see

Functions of Grit Use. 103

Another common mineral often used as grit is feldspar. Like quartz, feldspar is relatively hard and insoluble. Scott and Heuser (1957) found that domestic chicks, laying hens, and turkeys all preferred feldspar grit to granite when offered a choice, although the two grit types were consumed in equal amounts when fed singly. Among wild birds, the use of feldspar has been documented in Colorado White-tailed Ptarmigan (May and Braun 1973), in Rock Ptarmigan and

Willow Ptarmigan in Norway (Myrberget et al. 1975), in Red Grouse in the British Isles (Smith and

Rastall 1911), and in many North American species (Gionfriddo and Best, unpubl. data). In each instance, however, birds used less feldspar than quartz.

AMOUNT USED

Quantities of grit used by birds vary greatly within and among species, from none or a few particles to several hundred or more (e.g.. Sharp and McClure 1945, Westerskov 1965, Myrberget et al. 1975, Best and Gionfriddo 1991a). A Ring-necked Pheasant gizzard contained 2,709 grit particles; another contained a total grit volume of 19 cc (Westerskov 1965). Keil (1973) reported that grit accounted for more than half of the gizzard contents (by weight) of House Sparrows (66%) and

Eurasian Tree Sparrows (54%). Grit made up more than half (by volume) of the gizzard contents of California Quail in summer and winter, and more than one-quarter in spring and fall (Crispens et al. 1960). In some waterfowl and wading birds, half (Meinertzhagen 1954) or even three-quarters (Bengtson and Svensson 1968) of the volume of a full gizzard may be grit. In some of these species, however, grit ingestion may occur inadvertently during foraging in sandy

substrates. Several factors may influence the quantity of grit birds consume intentionally. These include the bird's age, diet, sex and reproductive status, and the characteristics of the grit particles.

Grit use often varies with the age of the bird. Nestlings of many species are fed grit by

their parents (Kluijver 1950; Miller 1962; Verbeek 1967,1970; Betts 1955; Royama 1970; Davis and 104

Arnold 1972; H&gvar and 0stbye 1976; Barrentine 1980; Alonso 1985; Bishton 1986; Mayoh and Zach 1986). Evidently this feeding is deliberate rather than incidental (Betts 1955, Royama 1970,

Crook 1975, Hogstad 1988), and it may begin soon after hatching (Higvar and 0stbye 1976). Betts (1955) watched both Great and Blue Tits at the nest and found that adult birds brought beakfuls of grit to the nest and fed a little to each of the young. Kluijver (1950) observed the collection and delivery to the nest of grit by adult Great Tits. Royama (1970) determined that Great Tits brought to the nest an average of about 1 beakful of grit or snail shell per nestling each day. Precocial young may start to use grit within a day of hatching. Northern Bobwhite (Stoddard 1931) and

Ruffed Grouse (Bump et al. 1947) chicks, for example, pick up grit almost as soon as they begin feeding. Grit has been found in crops (Dalke 1938) and gizzards (Westerskov 1965) of 1-day-old

Ring-necked Pheasants. Several studies have documented an increase and then a decrease with age in grit ingestion by nestlings of various species (Royama 1970, Barrentine 1980, Mayoh and

Zach 1986). Adults of many species, including Tree Swallow, House Wren (Mayoh and Zach

1986), Water Pipit (Verbeek 1970), Meadow Pipit (H&gvar and 0stbye 1976), and Homed Lark (McAtee 1905; but see Verbeek 1967) have been found to have less grit in their gizzards than nestlings. Juvenile Spanish Sparrows used significantly less grit (by weight) than nestlings (Alonso

1985). On the other hand, the quantity of gizzard grit increased with the age of the birds among juveniles of three species of Manitoba waterfowl investigated by Bartonek (1969). Ontogenetic shifts in grit use may be related to diet. For example, the dietary composition of nestlings of many species changes as the birds grow older. Alonso (1985) documented decreases in the weight and size of grit used by juvenile Spanish Sparrows that were strongly correlated with a decrease in the mean size of their prey. Harper (1963) found that as young Ring-necked Pheasants grew they consumed more grit but the proportion of calcium in that grit decreased. 105

Diet probably has a major effect on grit use through its influence on the value of grit as a grinding agent and mineral supplement. Use of insoluble grit had a greater beneficial influence on digestive efficiency in chickens consuming coarse rather than flne foods (Fritz 1937, Balloun and

Phillips 1956, Smith and Maclntyre 1959, Mcintosh et al. 1962). A general association between greater use of grit and diets consisting of hard, coarse food is evident among wild birds. Analysis of the gizzard contents of 1,440 North American birds determined that gizzards of granivores contained more grit particles than those of insectivores and omnivores (Gionfriddo and Best, unpubl. data). Gizzards of Red-winged Blackbirds in Manitoba (Bird and Smith 1964) and South

Dakota (Mott et al. 1972) contained more grit when birds consumed seeds than when they ate insects. Similarly, Bearded Tits used grit in winter when eating seeds, but not in summer when consuming mostly insects (Spitzer 1972 [dted in Welty and Baptista 1988]). Spanish Sparrows used more grit particles in fall and winter when they fed mainly on (relatively hard) small weed seeds than in spring and summer when they consumed large insects and cereal grains (Alonso 1985).

The amounts of grit in the gizzards of Common Eiders (Player 1971), Dunnocks (Bishton 1986),

Wood Pigeons (Mathiasson 1972), Capercaillie (Wilhelm 1982), Dickcissels (Zimmerman 1963), and three species of doves (Passmore 1981) also varied seasonally with diet. Grit use by juvenile

Spruce Grouse in Alberta increased steadily as the proportion of arthropods in the birds' diet decreased and plant parts became predominant (Pendergast and Boag 1970). Gizzards of herbivorous Australian (Norman and Brown 1985) and South African (Skead and Mitchell 1983) waterfowl species contained more grit (by weight) than those of carnivorous species. Captive

Norwegian Willow Ptarmigans fed twigs and buds of willow fSalix't and birch fBetula^ consumed and eliminated 2 to 4 times as many grit particles as those fed pelleted food (Norris et al. 1975). 106

For a discussion of the increased use of calcareous grit among birds with elevated calcium requirements, see Functions of Grit Use.

Differences in grit use between the sexes are not always evident (Siegfried 1973; Alonso

1985; Norman and Brown 1985; Garcher and Carroll 1991; Gionfriddo and Best 1995, unpubl. data).

When present, such differences may reflect the increased calcium requirements of females during egg laying and the ability of reproductive females to adjust their consumption of calcareous grit to meet these needs (Taylor 1970). For example, egg-laying Ring-necked Pheasant hens collected in

Minnesota and South Dakota consumed 50% more grit (by weight) than non-la5dng females, and their grit was about 4 times as rich in caldum as that of non-layers (Kopischke and Nelson 1966).

The amount of grit in gizzards of female House Sparrows peaked during the egg-laying period

(Pinowska and Krainicki 1985). Dalke (1938) found that the amount of grit in gizzards of Ring- necked Pheasants in Michigan increased during the breeding season and noted that the size of the increase was greater in females than in males. Several studies have documented an annual peak in

May in the amount of grit in gizzards of free-ranging (Harper 1964, Korschgen 1964, Kopischke

1966) and captive (Sadler 1961) Ring-necked Pheasants. Even in bird populations that use predominantly insoluble grit, females sometimes consume significantly more grit than males (May and Braun 1973).

Characteristics of the grit itself, especially size and composition, also may influence the amount of grit birds consume. Field studies have determined that, in general, the greater the size of the grit particles, the fewer are present in gizzards (Myrberget et al. 1975, Norris et al. 1975,

Alonso 1985, Best and Gionfriddo 1991a, Gionfriddo and Best 1995). When captive House

Sparrows were given either large (1.0 -1.4 mm) or small (0.2 - 0.4 mm) grit, gizzards of birds consuming large grit contained only one-fifth as many particles as those of birds consuming small 107 grit (5? = 51 vs. 275, respectively) (Gionfriddo and Best 1995). Grit composition affects the amount of grit birds consume in at least 2 ways. Birds may adjust calcareous grit consumption in accordance with fluctuating caldum requirements (see Functions of Grit Use). Also, some grit types dissolve/disintegratemore rapidly in the gizzard than others (e.g., limestone vs. quartz) and require more frequent replacement (Lienhart 1953, Smith and Madntyre 1959, Kopischke and

Nelson 1966).

Another factor affecting the amount of grit consumed by birds is its availability (Bump et al. 1947, Tindall 1973, Norris et al. 1975). Under normal ecological conditions, some birds occasionally face situations in which grit is temporarily unavailable. For example, in temperate zones snow occasionally may cover all or most sources of grit. Under such circumstances birds must either emigrate or conserve the grit already in their gizzards. Some birds leave local areas after snow has covered their grit supplies (Meinertzhagen 1954,1964; Selden and Smith 1978).

PuUiainen and livanainen (1981) noted that Willow Ptarmigan readily exploited grit resources on wind-swept summits and suggested that these sites were visited specifically for the grit. On the other hand, it is likely that the ability to conserve grit is well developed in many avian species (see

Retention Time). Several studies have demonstrated that birds are able to sharply reduce grit elimination rates in response to the removal of ingestable grit (e.g.. Brown 1904, Smith and Rastall

1911, McCann 1939).

RETENTION TIME

The ability of birds to retain grit in the gizzard for extended periods has long been recognized (Kraupp and Ivey 1923, Kraupp 1924, Anonymous 1937), and grit is known to have been retained in the gizzards of birds for up to 1 year (Table 2). The mechanisms of retention remain unknown, but control by the gizzard seems likely. McCann (1939) suggested that the 108 pyloric sphincter (at the outlet of the gizzard) may determine which particles are retained.

Mathiasson (1972) concluded from field and experimental evidence that the tj^e of food eaten has an immediate effect on the process that regulates grit retention in the gizzard. He suggested that tactile receptors in the gizzard mucosa receive information on the number of grit particles present, and that the consistency (hardness or softness) of the food in the gizzard determines the rate at which grit particles contact these receptors. The number of particles retained therefore depends on the hardness of the food. Others also have suggested that gastrointestinal stimuli regulate grit intake and retention, in accordance with the consistency of the food eaten (Beer and Tidyman 1942,

Porkert 1972, Porkert and Hoglund 1984).

The retention of grit particles in the gizzard is influenced by the rate at which grit is ingested (Walter and Aitken 1961, Tagami 1974, Trost 1981). When grit is readily available, birds may consume and eliminate considerable amounts daily (Brown 1904, Lienhart 1953, May and

Braun 1973, Alonso 1985, Gionfriddo and Best 1995). Birds suddenly deprived of grit, however, can reduce their grit output and retain particles in their gizzards for long periods (Smith and

Rastall 1911, Kraupp 1924, McCann 1939, Walter and Aitken 1961). May and Braun (1973) found

that Colorado White-tailed Ptarmigan living in quartz-defident areas selected quartz as grit and retained it longer than birds living in areas where quartz was more readily available. Hoskin et al.

(1970) concluded that Alaskan Rock Ptarmigan retained grit longer in winter when snow cover

sharply reduced the availability of grit, and Stoddard (1931) suggested that Northern Bobwhites did

the same.

Other factors that influence grit retention in the gizzard include diet and grit characteristics

(particle size, shape, composition) (Hollingsworth et al. 1965). Diet can affect retention in at least 2

ways. Coarse, hard diets may increase the grit ingestion rate and thereby reduce retention (Trost 109

1981). Hard diets also may reduce retention by accelerating grit particle disintegration and elimination (Norris et al. 1975).

To what extent the gizzard is selective in its retention of individual grit particles, as suggested by Kraupp and Ivey (1923), is not clear. In several laboratory studies, groups of birds were fed (ad libitum) grit of different sizes (one size per group). Smith (1960) measured grit consumption and determined that as grit size increased, so did the proportion that was retained in gizzards of domestic chicks. Tagami (1974) found that domestic chicks retained more medium-sized (1.7 - 2.4 mm) grit particles than large (2.4 - 3.4 mm) particles, and that they retained very few small (0.6 -1.7 mm) particles. In gizzards of captive House Sparrows, on the other hand, small grit particles were retained longer than large particles (Gionfriddo and Best 1995). Retention processes in gizzards of free-ranging birds, however, act on a much wider range of grit sizes than were made available to these experimental birds (Best and Gionfriddo 1991a).

Grit particle shape also may affect retention. For example, domestic chicks offered grit of 2

different shapes consumed more smooth-surfaced grit, but their gizzards retained a higher

proportion of the rough-surfaced grit particles they ingested (Smith 1960). The comparative

retention of rounded versus angular grit particles was evaluated in 2 experiments in which captive

House Sparrows were administered (dosed via oral gavage; N = 23) or fed (mixed with canned dog

food; M = 15) equal amounts of the 2 grit types for a period of time, deprived of grit for 2 days,

and then examined (Gionfriddo and Best, unpubl. data). In both experiments, the proportions of

the 2 grit types did not differ significantly in most gizzards. When they did differ, angular grit

predominated in gizzards in the oral gavage experiment (8 of 9 gizzards), whereas rounded grit

predominated in the dog food experiment (5 of 5 gizzards). These results suggest that particle

shape generally does not strongly influence grit retention, although there may be a tendency to 110 retain angular grit when the diet consists of hard foods (birds in the oral gavage experiment were fed a seed mixture) and to retain rounded grit when softer foods (represented by canned dog food) are consumed.

Whether the excessive accumulation of grit in the gizzard is prevented by periodic evacuations of the gizzard (Trost 1981) or by a slower, more constant turnover is unknown. To examine grit turnover in gizzards, Gionfriddo and Best (1995) switched captive House Sparrows from one hard, insoluble grit type to a second, very similar grit. Only 6 hours after the switch, nearly 40% of the grit in gizzards of these birds was of the second grit type; after 24 hours only

12% was of the first grit type. The hardness and solubility of grit particles influence grit replacement in the gizzard. Grit disintegration in the gizzard may be substantial (Korschgen et al.

1965, Vance 1971, Norris et al. 1975). Lienhart (1953) found that small calcium fragments dissolved completely in 3 hours in chickens' gizzards. Experiments with captive House Sparrows given crushed marble (calcium carbonate) grit and fed a seed mixture indicated a more moderate disintegration rate: at least 3 months would have been required for the complete dissolution of particles 0.4 - 0.7 mm in size (Gionfriddo and Best, unpubl. data). Physical and chemical alteration of less soluble grit particles are much less rapid, permitting longer retention in the gizzard

(Lienhart 1953, Smith and Maclntyre 1959, Kopischke and Nelson 1966).

GRIT SUBSTmJTES

Birds often consume non-food items other than stones and rock fragments. These items are sometimes retained in the gizzard where they seem to function as grit substitutes. Among the materials found in birds' gizzards and reportedly serving as grit were hard seeds, insect parts, small snails and shells, shell fragments, fossils, lead shot, bones, teeth, and coral (Table 3). Ill

Grit availability and the specific food habits of a species seem to determine to what extent hard seeds are used as a substitute for grit particles (Beer and Tidyman 1942). Even when grit is available, however, some birds use hard seeds instead. In their study of 9 free-ranging gallinaceous and 1 passerine species, Beer and Tidyman (1942) documented a supplanting of grit by hard seeds in the gizzards of at least 6 avian species. They found that the volume of grit and the volume of hard seeds were inversely proportional, i.e., the sum of the 2 volumes remained constant. The authors concluded that some birds may be able to control the total volume of hard material in their gizzards.

Results of several other studies also provide evidence that birds may substitute hard seeds for grit. Lewin and Lewin (1984) examined the gizzards of Kalij Pheasants introduced on the island of Hawaii and found that they contained 2 to 300 lava particles and 0 to 472 hard seeds. A strong negative correlation was found between the numbers of grit particles and the numbers of hard seeds in these gizzards. In Australia, Norman and Mumford (1985) found a moderate negative correlation between the volumes of grit and hard seeds in Purple Swamphen gizzards.

Carroll (1966) had suggested that Purple Swamphens substituted hard seeds for grit during summer and autumn, and had used this to explain the decreased use of grit during those seasons.

An inverse relationship between the numbers of grit particles and hard seeds in gizzards of Ring- necked Pheasants in Nebraska was attributed to greater use of hard seeds as grinding agents in the sandhill region, where suitable grit generally is unavailable (Sharp and McCIure 1945). Swanson and Bartonek (1970) found that hard seeds were retained in gizzards of captive Blue-winged Teal for several days while softer foods were eliminated and suggested that they were functioning as grit. 112

Fragments of insects and shells often are used as grit (Table 3). Jenldnson and Mengel

(1970) speculated that the large, undigested beetle heads they found in the gizzards of about one-third of the 46 Central and South American Common Pauraques they examined were serving as substitutes for grit. In some instances these beetle heads were the only items retained in the gizzards. Bird and Smith (1964) found less grit in gizzards of Red-winged Blackbirds when hard insect parts were retained, and suggested that these insect parts had replaced grit as grinding agents. Korschgen (1964) suggested that the caldum-rich snails consumed by Missouri

Ring-necked Pheasants were used in lieu of calcareous grit where the latter was not plentiful or readily available.

Pestidde Granules

Granular pesticides are applied to millions of hectares of com and other crops each year in

North America to control agricultural pests (U.S. Dep. Agric. 1992). Pesticide granules are often spilled or not fully incorporated into the soil during application, making them accessible to birds

(Erbach and Tollefson 1991). The toxicity of these materials to birds (Balcomb et al. 1984, Hill and

Camardese 1984) has prompted interest in evaluating avian risk associated with pesticide use.

There are several potential sources of avian exposure to granular pesticides, including consumption of the gi-anules as a source of grit (Best and Fischer 1992). Characteristics of pesticide granules often are similar to those of grit particles used by birds (Best 1992). Most pesticide granules disintegrate rapidly in the gizzard (Best and Gionfriddo 1991b) and therefore probably do not satisfy a bird's "appetite" for grit, although the action of the chemical may diminish this appetite.

Moreover, for several pesticides, the consumption of five or fewer granides is lethal to passerine birds (Balcomb et al. 1984). 113

Several potential means of reducing avian consumption of pesticide granules as a source of grit have been proposed (Best and Fischer 1992). In addition to improving pesticide application techniques, the suggestions include altering granule characteristics such as size, shape, surface texture, color, composition, and insecticide load. The option(s) chosen would depend on whether the goal was to make the granules less conspicuous/attractiveto birds (so they would be less likely to be seen and consumed) or more conspicuous/attractive(so an aversive response could be more easily learned [e.g.. Mason and Reidinger 1983, Roper and Redston 1987] if toxicity per granule were sufficiently low). Alteration of pesticide granule color may be the most feasible and promising means of changing the conspicuousness/attractiveness of pesticide granules as a source of grit (Best and Fischer 1992; Gionfriddo and Best, unpubl. data).

Lead Shot

Lead poisoning of waterfowl and shorebirds in and near wetlands in North America has

been a problem for more than a century (Phillips and Lincoln 1930, Knap 1969). More recently, lead poisoning also has become more common at many upland sites (e.g., Locke and Bagley 1967

and refs. therein, Lewis and Legler 1968, Castrale 1989). Lead shot may enter birds' bodies by

being "shot in" by hunters, by being inadvertently ingested by foraging birds, or by being mistaken

for food or grit and consumed. The focus of the present discussion is the retention of lead shot in

the gizzard where it may serve as a grit substitute.

Birds need not consume many lead pellets to receive a lethal dose of lead. Among captive

Mallards experimentally dosed with lead shot, mortality rates were 35% for birds receiving 2 pellets

and 54% for those given 4 (Godin 1967). Wetmore (1919) noted that wintering areas where lead

poisoning occurred often were deficient in grit, and he suggested that grit be provided in such

areas. Godin (1967) found that, for a given dose of lead pellets, there were no significant 114 differences in mortality rates among Mallards given different tjrpes of grit (no grit, coarse sand, mica granite, or crushed oyster shell). Providing supplementary grit therefore may reduce lead poisoning only if birds consume grit instead of (and not in addition to) lead pellets.

Susceptibility to lead poisoning depends on many factors, including a bird's body size, feeding habits and locations, diet, and requirements for grit. Spray and Milne (1988) found that lead poisoning mortality in Scotland was much greater in Whooper Swans than in Mute Swans, and that gizzards of Whoopers contained more grit and more lead pellets. They concluded that the Whoopers' greater need for grit contributed to its greater mortality from lead poisoning. Hall and Fisher (1985) reported that among birds using brackish waters in Texas, those species that used relatively large proportions of grit larger than 2.0 mm in diameter were much more likely to ingest lead pellets than species that used smaller grit. Noting that suitable grit often is limited in northern Texas gulf coast marshes, they suggested that lead shot was consumed instead of grit by some avian species. More than 97% of the grit in gizzards of Canada Geese in Wisconsin was smaller than the lead shot found in some (9%) of the gizzards, suggesting that geese were not intentionally using lead pellets as grit (Craven and Hunt 1984). A massive die-off of Canada Geese

(> 900 birds) due to lead poisoning in Colorado was attributed to the intentional consumption of lead shot on the ground surface in agricultural fields adjacent to a heavily-hunted pond (Szjmiczak and Adrian 1978). It was not clear if the birds mistook the lead pellets for food or grit, but samples

of the availability of various pellet sizes on the ground indicated that the geese seemed to

preferentially consume the larger (> No. 4) shot sizes.

SUMMARY

Grit is ingested and retained in the gizzards of most species of birds that eat plant parts

and many that eat insects. Most research on avian grit use has focused on upland game birds. 115 waterfowl, and poultry. Grit aids in the mechanical grinding of coarse, hard foods in the gizzard.

Sometimes it also provides critical nutrients such as calcium, the demand for which is especially great in rapidly-growing young and in egg-la}ing females. Characteristics of grit that influence its use by birds include particle size, shape, color, and composition. The size of grit birds use depends upon grit availability and the bird's age, diet, and body size. The extent to which grit shape and surface texture influence avian grit use has received little attention, but captive birds in experimental settings have shown grit preferences based on these features. Grit color greatly influences grit selection by captive birds. The composition of grit may play a major role in avian grit use because grit types differ in their value as grinding agents and nutrient sources, and in their dissolution/disintegrationrates in the gizzard. Quartz generally predominates in birds' gizzards, but some free-ranging birds preferentially consume limestone or other caldum-rich grit.

Grit availability and the birds' specific needs determine the selection of grit types. The amounts of grit in birds' gizzards vary greatly and are influenced by bird age, diet, nutritional and reproductive status, and by the characteristics of the grit particles. Although most grit particles probably pass through the digestive tract in a few hours, some may be retained in the gizzard for many months. The mechanism of retention and its degree of selectivity are unknown. Evidence suggests that particle size, shape, surface texture, and composition, in addition to grit consumption rate, may affect particle retention. In place of grit, other non-food items are sometimes consumed and then retained in the gizzard. Like grit, these items may serve as grinding agents and, in some instances, they may provide supplementary nutrients. Pesticide granules and lead shot are sometimes ingested as grit, often with fatal results. Grit use may not be necessary for the survival of birds, but it is an important dietary component for many birds through its nutritional benefits. 116

ACKNOWLEDGMENTS

J. J, Dinsmore, E, E. Klaas, J. L. Sell, and K. C. Shaw reviewed an earlier draft of the manuscript and offered helpful suggestions. Funding was provided by Miles, Inc., Rhone- Poulenc, American Cyanamid, and Dow Elanco.

LITERATURE CITED

Allen, D. L. 1962. Our wildlife legacy, 2nd ed. Funk and Wagnalls, New York. 422 pp.

Alonso, J. C. 1985. Grit in the gizzard of Spanish Sparrows (Passer hispaniolensis). Vogelwarte

33:135-143.

Anderson, H. G. 1959. Food habits of migratory ducks in Illinois. Bull. 111. Nat. Hist. Surv.

27:289-344.

Anderson, W. L., and P. L. Stewart. 1969. Relationships between inorganic ions and the

distribution of pheasants in Illinois. J. Wildl. Manage. 33:254-270.

Anderson, W. L., and P. L. Stewart. 1973. Chemical elements and the distribution of pheasants

in Illinois. J. Wildl. Manage. 37:142-153.

Anonymous. 1937. Grit and dust. I.C.I. Game Researches Advisory Leafl. No. 3. 8 pp.

Balcomb, R., R. Stevens, and C. Bowen n. 1984. Toxicity of 16 granular insecticides to wild-caught

songbirds. Bull. Environ. Contam. and Toxicol. 33:302-307.

Balloun, S. L., and R. E. Phillips. 1956. Grit feeding affects growth and feed utilization of chicks

and egg production of laying hens. Poult. Sd. 35:566-569.

Barlow, J. C., E. E. Klaas, and J. L. Lenz. 1963. Sunning of Bank and Cliff swallows. Condor

65:438-440.

Barrentine, C. D. 1980. The ingestion of grit by nestling Bam Swallows. J. Field Omithol.

51:368-371. 117

Bartonek, J. C. 1969. Build-up of grit in three pochard species in Manitoba. Wilson Bull. 81:96-97.

Beer, J., and W. Tidyman. 1942. The substitution of hard seeds for grit. J. Wildl. Manage.

6:70-82.

Bengtson, S., and B. Svensson. 1968. Feeding habits of Calidris alpina L. and £. minuta Leisl.

(Aves) in relation to the distribution of marine shore invertebrates. Oikos 19:152-157.

Best, L. B. 1992. Characteristics of com rootworm insecticide granules and the grit used by

cornfield birds: evaluating potential avian risks. Am. Midi. Nat. 128:126-138.

Best, L. B., and D. L. Fischer. 1992. Granular insecticides and birds: factors to be considered in

understanding exposure and reducing risk. Environ. Toxicol, and Chem. 11:1495-1508.

Best, L. B., and J. P. Gionfriddo. 1991a. Characterization of grit use by cornfield birds. Wilson

Bull. 103:68-82.

Best, L. B., and J. P. Gionfriddo. 1991b. Integrity of five granular insecticide carriers in House

Sparrow gizzards. Environ. Toxicol, and Chem. 10:1487-1492.

Best, L. B., and J. P. Gionfriddo. 1994. Effects of surface texture and shape on grit selection by

House Sparrows and Northern Bobwhite. Wilson Bull. 106:689-695.

Betts, M. M. 1955. The food of titmice in oak woodland. J. Anim. Ecol. 24:282-323.

Bird, R. D., and L. B. Smith. 1964. The food habits of the Red-winged Blackbird, Agelaius

phoeniceus. in Manitoba. Can. Field-Nat. 78:179-186.

Bishton, G. 1986. The diet and foraging behaviour of the Dunnock Prunella modularis in a

hedgerow habitat. Ibis 128:526-539.

Boag, D. A. 1963. Significance of location, year, sex, and age to the autumn diet of Blue Grouse.

J. Wildl. Manage. 27:555-562. 118

Bolen, E. G., and B. J. Forsyth. 1967. Foods of the Black-bellied Tree Duck in soutfi Texas.

Wilson BuU. 79: 43-49.

Brook, H. T, 1957. Insoluble grit cuts feeding costs. Modem Poult. Keeping 76:5-7.

Brown, C. R. 1976. Use of gravel by Purple Martins. Auk 93:842.

Brown, E. W. 1904. Digestion experiments with poultry. U.S. Dep. Agric. Bur. Anim. Ind. Bull.

56.

Brunner, H., and B. J. Coman. 1983. The ingestion of artificially coloured grain by birds, and its

relevance to vertebrate pest control. Aust. Wildl. Res. 10:303-310.

Buckner, G. D., and J. H. Martin. 1922. The function of grit in the gizzard of the chicken. Poult.

Sd. 1:108-113.

Buckner, G. D., J. H. Martin, and A. M. Peter. 1923. [unknown title.] Ky. Agric. Exp. Stn.

Research Bull. No. 250. [Cited in Buckner et al. 1926.]

Buckner, G. D., J. H. Martin, and A. M. Peter. 1926. Concerning the growth of chickens raised

without grit. Poult. Sd. 5:203-208.

Bump, G., R. W. Darrow, F. C. Edminster, and W. F. Crissey. 1947. The Ruffed Grouse: life

history, propagation, management. N.Y. State Conserv. Dep., Albany. 915 pp.

Burrows, W. H. 1936. The surgical removal of the gizzard from the domestic fowl. Poult. Sd.

15:290-293.

Campbell, R. R., and J. F. Leatherland. 1983. Changes in caldum reserves in breeding Lesser

Snow Geese (Chen caerulescens caerulescens^. Acta Zool. 64:9-14.

Carroll, A. L. K. 1966. Food habits of Pukeko (Porphyrio melanotus Temminck). Notomis

13:133-141. 119

Castrale, J. S. 1989. Availability of spent lead shot in fields managed for Mourning Dove hunting.

Wildl. Soc. BuO. 17:184-189.

Chabreck, R. H., T. Joanen, and S. L. Paulus. 1989. Southern coastal marshes and lakes. Pages

249-277 in L. M. Smith, R. L. Pederson, and R. M. Kaminski, eds. Habitat management

for migrating and wintering waterfowl in North America. Texas Tech, Univ. Press,

Lubbock.

Chambers, G. D. 1963. Com a staple food of doves wintering in northern Missouri. J. Wildl.

Manage. 27:486-488.

Classen, H. L., and T. A. Scott. 1982. Self-selection of calcium during the rearing and early laying

periods of white leghorn pullets. Poult. Sd. 61:2065-2074.

Cottam, C. 1929. The status of the Ring-necked Pheasant in Utah. Condor 31:117-1123.

Craven, S. R., and R. A. Hunt. 1984. Fall food habits of Canada Geese in Wisconsin. J. Wildl.

Manage. 48:169-173.

Crook, D. 1975. Chipping Sparrows feeding grit to offspring. Wilson Bull. 87:552.

Dale, F. H. 1954. Influence of calcium on the distribution of the pheasant in North America.

Trans. N. Amer. Wildl. Conf. 19:316-323.

Dale, F. H. 1955. The role of calcium in reproduction of the Ring-necked Pheasant. J. Wildl.

Manage. 19:325-331.

Dale, F. H., and J. B. DeWitt. 1958. Calcium, phosphorus and protein levels as factors in the

distribution of the pheasant. Trans. N. Am. Wildl. Conf. 23:291-294.

Dalke, P. D. 1938. Amount of grit taken by pheasants in soutiiem Michigan. J. Wildl. Manage.

2:53-54. 120

Darby, D. G., and R. W. Ojakangas. 1980. Gastroliths from an Upper Cretaceous plesiosaur. J.

Paleontol. 54:548-556.

Davis, J. P., C. H. Thomas, and L. L. Glasgow. 1961. Foods available to waterfowl in fallow

ricefields of soudiwest Louisiana, 1960-1961. Proc. Annu. Conf. Southeast. Game and Fish

Comm. 15:60-66.

Davis, W. R. U., and K. A. Arnold. 1972. Food habits of the Great-tailed Grackle in Brazos

County, Texas. Condor 74:439-446.

Duecker, G., and L Schulze. 1977. Color vision and color preference in Japanese Quail fCotumix

cotumix japonica) with colorless oil droplets. J. Comp. Physiol. Psychol. 91:1110-1117.

Eisenhauer, D. I., and C. M. Kirkpatrick. 1977. Ecology of the Emperor Goose in Alaska. Wildl.

Monogr. 57:1-62.

Elliott, B., and S. W. Hinners. 1969. Effect of certain dietary variables on the chick's response to

grit. Poult. Sd. 48:1804-1805.

Ellison, L. N. 1966. Seasonal foods and chemical analysis of winter diet of Alaskan Spruce

Grouse. J. Wildl. Manage. 30:729-735.

Ellison, L. N. 1974. Population characteristics of Alaskan Spruce Grouse. J. Wildl. Manage.

38:383-395.

Erbach, D. C., and J. J. Tollefson. 1991. Application of com pesticide granules to minimize hazard

to birds. Applied Engineer. Agric. 7:545-548.

Errington, P. L. 1931. The bobwhite's winter food. Am. Game 20:75-78.

Famer, D. S. 1960. Digestion and the digestive system. Pages 411-467 in A. J. Marshall, ed.

Biology and comparative physiology of birds. Academic Press, New York. Ferrel, C. M., H. Twining, and N. B. Herkenham. 1949. Food habits of the Ring-necked Pheasant

(Phasianus colchicus^ in the Sacramento Vallev. California. Calif. Fish and Game 35:51-69.

Fischer, G. J., G. L. Morris, and J. P. Ruhsam. 1975. Color pecking preferences in white leghorn

chicks. J. Comp. Physiol. Psychol. 88:402-406.

Fischer, G. J., and S. J. Davis. 1981. Brightness effects on color pecking preferences in

dark-hatched domestic chicks. Dev. Psychobiol. 14:237-249.

Fisher, H. 1972, The nutrition of birds. Pages 431-469 in D. S. Famer, J. R. King, and K. C.

Parkes, eds. Avian biology, vol. 2. Academic Press, New York.

Forbes, H. O. 1892. On a recent discovery of the remains of extinct birds in New Zealand.

Nature 45:416-418.

Fox, A. C. 1941. Winter feeding for game birds. N.D. Fish and Game Dep., Bismarck, N.D. 16

pp. [Cited in Robel and Bisset 1979.]

Fritz, J. C. 1937. The effect of feeding grit on digestibility in the domestic fowl. Poult. Sd.

16:75-79.

Fritz, J. C., W. H. Burrows, and H. W. Titus. 1936. Comparison of digestibility in

gizzardectomized and normal fowls. Poult. Sd. 15:239-243.

Garcher, M. L., and J. P. Carroll. 1991. Comparative diet study of male and female Wilson's

Phalaropes in North Dakota. J. Pa. Acad. Sd. 64 (Suppl.):190.

Gendron, R. P. 1986. Searching for cryptic prey: evidence for optimal search rates and the

formation of search images in quail. Anim. Behav. 34: 898-912.

Gerstell, R. 1937. The status of the Ringneck Pheasant in Pennsylvania. Trans. N. Am. Wildl.

Conf. 2:505-511. 122

Gerstell, R. 1942. The place of winter feeding in practical wildlife management. Pa. Game

Comm. Res. Bull. 3. 121 pp.

Gionfriddo, J. P., and L. B. Best. 1995. Grit use by House Sparrows: effects of diet and grit size.

Condor, in press.

Gittleman, J. L., and P. H. Harvey. 1980. Why are distasteful prey not cryptic? Nature 286:149-

150.

Gittleman, J. L., P. H. Harvey, and P. J. Greenwood. 1980. The evolution of conspicuous

coloration: some experiments in bad taste. Anim. Behav. 28:897-899.

Godin, A. J. 1967. Test of grit t3^es in alleviating lead poisoningin Mallards. U.S. Dep. Inter.,

Fish and Wildl. Serv., Spec. Sd. Rep., Wildl. No. 107. 9 pp.

Goforth, W. R., and T. S. Baskett. 1971. Effects of colored backgrounds on food selection by

penned Mourning Doves fZenaidura macroura^. Auk 88:256-263.

Gordon, S. 1925. Winter feeding of game. Pa. Board of Game Comm., Harrisburg, Pa. 4 pp.

[Cited in Robel and Bisset 1979.]

Gudmundsson, F. 1972. Grit as an indicator of the overseas origin of certain birds occurring in

Iceland. Ibis 114:582.

Higvar, S., and E. 0stbye. 1976. Food habits of the Meadow Pipit Anthus pratensis (L.) in alpine habitats at Hardangervidda, south Norway. Norw. J. Zool. 24:53-64.

Hall, S. L., and F. M. Fisher Jr. 1985. Lead concentrations in tissues of marsh birds: relationship

of feeding habits and grit preference to spent shot ingestion. BuU. Environ. Contam.

Toxicol. 35:1-8.

Halse, S. A. 1983. Weight and particle size of grit in gizzards of Spur-winged Geese. Ostrich

54:180-182. 123

Harper, J. A. 1963. Calcium in grit consumed by juvenile pheasants in east-central Illinois. J.

Wildl. Manage. 27:362-367.

Harper, J. A. 1964. Calcium in grit consumed by hen pheasants in east-central Illinois. J. Wildl.

Manage. 28:264-270.

Harper, J. A., and R. F. Labisky. 1964. The influence of caldum on the distribution of pheasants

in Illinois. J. Wildl. Manage. 28:722-731.

Harrisson, T. 1954. [untitled letter]. Ibis 96:626.

Hess, E. H. 1956. Natural preferences of chicks and ducklings for objects of different colors.

Psychol. Rep. 2:477-483.

Heuser, G. F., and L. C. Norris. 1946. Calcite grit and granite grit as supplements to a chick

starting ration. Poult. Sd. 25:195-198.

Hicks, C. L. 1940. Emergency feeding of game and song birds in winter. Oh. St. Univ., Oh.

Wildl. Res. Stn. Release 154. 10 pp. [Cited in Robel and Bisset 1979.]

Hill, E. P., and M. B. Camardese. 1984. Toxidty of anticholinesteraseinsectiddesto birds:

technical grade versus granular formulations. Ecotoxicol. and Environ. Safety 8:551-563.

Hogstad, O. 1988. Foraging pattern and prey selection of breeding Bramblings Fringilla

montifringilla. Fauna Norv. Ser. C, Cindus 11:27-39.

Hollingsworth, H., J. R. Howes, and J. Geary. 1965. The intake and fate of insoluble grit as

studied with x-rays and as affected by environment. Poult. Sd. 44:1380.

Hoskin, C. M., R. D. Guthrie, and B. L. P. Hoffman. 1970. Pleistocene, Holocene and Recent bird

gastroliths from interior Alaska. Arctic 23:14-23.

Hughes, B. O. 1972. A circadian rhythm of caldum intake in the domestic fowl. Br. Poult. Sd.

13:485-493. Hughes, B. O., and D. G. M. Wood-Gush. 1971. A specific appetite for caldum in domestic

chickens. Anim. Behav. 19:490-499.

Jenkinson, M. A., and R. M. Mengel. 1970. Ingestion of stones by goatsuckers (Caprimulgidae).

Condor 72:236-237.

Jones, G. W. 1933. An apparently unnoticed trait of Whip-poor-will. Auk 50:436-437.

Jones, P. J. 1976. The utilization of calcareous grit by laying Ouelea quelea. Ibis 118:575-576.

Jonkel, C. J., and K. R. Greer. 1963. Fall food habits of Spruce Grouse in northwest Montana. J.

Wildl. Manage. 27:593-596.

Joshua, I. G., and W. J. Mueller. 1979. Thedevelopmentof a specific appetite for caldum in

growing broiler chicks. Br. Poult. Sd. 20:481-490.

Kalmbach, E. R., and J. F. Welch. 1946. Colored rodent baits and their value in safeguarding

birds. J. Wildl. Manage. 10:353-360.

Keil, W. 1973. Investigations on food of House-and Tree sparrows in a cereal-growing area

during winter. Pages 253-261 in S.C. Kendeigh and J. Pinowski, eds. Productivity,

population djmamics and systematics of granivorous birds. PWN - Pol. Sd. Publ.,

Warsaw, Poland.

Kluijver, H. N. 1950. Daily routines of the Great Tit, Parus m. major L. Ardea 38:99-135.

Knap, J. J. 1969. Lead poisoning in waterfowl. Can. Audubon 31(4-5):127-132.

Kolderup, C.F. 1925. (Grit in the gizzard of Norwegian Willow Grouse.) Bergens Mus. Aarb.

1923-1924, Naturvid. Raekke 4:1-34. [Cited in Myrberget et al. 1975, Selden and Smith

1978.]

Kopischke, E. D. 1966. Selectionof caldum-and magnesium-bearing grit by pheasants in

Minnesota. J. Wildl. Manage. 30:276-279. 125

Kopischke, E. D., and M. M. Nelson. 1966. Grit availability and pheasant densities in Minnesota

and North Dakota. J. Wildl. Manage. 30:269-275.

Korschgen, L. J. 1964. Foods and nutrition of Missouri and midwestem pheasants. Trans. N.

Am. Wildl. Nat. Resour. Conf. 29:159-180.

Korschgen, L. J., G. D. Chambers, and K. C. Sadler. 1%5. Digestion rate of limestone force-fed to

pheasants. J. Wildl. Manage. 29:820-823.

Koubek, P. 1986. The spring diet of the Woodcock fScolopax rusticola^. Folia Zool. 35:289-297.

Kovach,J. K. 1974. Early color preferences in the Cotumix quail. J. Comp. Physiol. Psychol.

87:1049-1060.

Kraupp, B. F. 1924. The digestive organs of the fowl. Vet. Med. 19:522-523.

Kraupp, B. F., and J. E. Ivey. 1923. Digestive coefficients of poultry feeds and rapidity of

digestion and fate of grit in the fowl. N.C. Agric. Exp. Stn. Tech. Bull. 22.

Leopold, A. 1931. Report on a game survey of the north central states. Sporting Arms and

Ammunition Manufacturers'Institute, Madison, Wis. 299 pp.

Lewin, V., and G. Lewin. 1984. The Kalij Pheasant, a newly established game bird on the island

of Hawaii. Wilson Bull. 96:634-646.

Lewis, J. C. 1993. Foods and feeding ecology. Pages 181-204 in T. S. Baskett, M. W. Sayre, R. E.

Tomlinson and R. E. Mirarchi, eds. Ecology and management of the Mourning Dove.

Stackpole Books, Harrisburg, Pa.

Lewis, J. C., and E. Legler, Jr. 1968. Lead shot ingestion by Mourning Doves and incidence in

soil. J. Wildl. Manage. 32:476-482.

Lienhart, R. 1953. Recherches sur le role des cailloux contenus dans le gesier des oiseaux granivores. Bull. Soc. Sd. Nancy 12:5-9. 126

Lifjeld, J. 1983. (Prey and grit taken by five species of waders at an autumn migration staging

post in N Norway.) Fauna Norv, Ser. C, Cinclus 7:28-36.

Lobaugh, B., I. G. Joshua, and W. J. Mueller. 1981. Regulation of calcium appetite in broiler

chickens. J. Nutr. 111:298-306.

Locke, L. N., and G. E. Bagley. 1967. Lead poisoning in a sample of Maryland Mourning Doves.

J. Wildl. Manage. 31:515-518.

Lumsden, H. G., and R. B. Weeden. 1%3. Notes on the harvest of Spruce Grouse. J. WildL

Manage. 27:587-591.

MacLean, S. F. Jr. 1974. Lemming bones as a source of calcium for arctic sandpipers fCalidris

spp.). Ibis 116:552-557.

March, G. L., and R. M. F. S. Sadleir. 1970. Studies on the Band-tailed Pigeon fColumba fasdata)

in British Columbia. L Seasonal changes in gonadal development and crop gland activity.

Can. J. ZooL 48:1353-1357.

March, G. L., and R. M. F. S. Sadleir. 1972. Studies on the Band-tailed Pigeon fColumba fasdata^

in British Columbia. II. Food resource and mineral-gravelling activity. Syesis 5:279-284.

Mason, J. R., and R. F. Reidinger Jr. 1983. Generalization of and effects of pre-exposure on

color-avoidance learning by Red-winged Blackbirds (Agelaius phoeniceus). Auk

100:461-468.

Mathiasson, S. 1972. (The relation between the number of grit stones and the type of food of

Wood Pigeons (Columba palumbus^^. Goteb. Naturhist. Mus. Arstryck 1972:13-22.

May, T. A., and C. E. Braun. 1973. Gizzard stones in adult White-tailed Ptarmigan (Lagopus

leucurus^ in Colorado. Arctic Alpine Res. 5:49-57. 127

Mayoh, K. R., and R. Zach. 1986. Grit ingestion by nestling Tree Swallows and House Wrens.

Can. J. Zool. 64:2090-2093.

McAtee, W. L. 1905. The Homed Larks and their relation to agriculture. U.S. Dep. Agric., Biol.

Surv. Bull. No. 23. 37 pp.

McCann, L. J. 1939. Studies of the grit requirements of certain upland game birds. J. Wildl.

Manage. 3:31-41.

McCann, L.J. 1961. Grit as an ecological factor. Am. Midi. Nat. 65:187-192.

McClure, H. E. 1941. Ecology and management of the Mourning Dove. Zenaidura macroura

(Linn.), in southwest Iowa. Ph.D. dissertation, Iowa St. Coll., Ames. 366 pp.

Mcllhenny, E. A. 1932. The Blue Grouse in its winter home. Auk 49:279-306.

Mcintosh, J. I., S. J. Slinger, I. R. Sibbald, and G. G. Ashton. 1962. Factors affecting the

metabolizable energy content of poultry feeds. 7. The effects of grinding, pelleting and grit

feeding on the availability of the energy of wheat, com, oats and barley. 8. A study on the

effects of dietary balance. Poult. Sd. 41:445-456.

McLelland, J. 1979. Digestive system. Pages 69-181 in A. S. King and J. McLelland, eds. Form

and function in birds, vol. 1. Academic Press, New York.

Meinertzhagen, R. 1954. Grit. Bull. Br. Omithol. Club 74:97-102.

Meinertzhagen, R, 1964. Grit. Pages 341-342 in A.L. Thomson, ed. A new dictionary of birds.

McGraw-Hill, New York.

Meyer, G. B., S. W. Babcock, and M. L. Sunde. 1970. Decreased feed consumption and increased

calcium intake associated with puUef s first egg. Poult. Sd. 49:1164-1169.

Miller, L. 1962. Stomach stones. Zoonooz 35:10-13. 128

Moksnes, A. 1988. Grit in the stomachs of Ringed Plovers Charadrius hiaticula and Temminck's

Stints Calidris temminckii during breeding. Fauna Norv. Ser. C, Cindus 11:7-10.

Mongin, P., and B. Sauveur. 1974. Voluntary food and calcium intake by the laying hen. Br.

Poult. Sd. 15:349-359.

Mott, D. F., R. R. West, J. W. De Grazio, and J. L. Guardino. 1972. Foods of the Red-winged

Blackbird in Brown County, South Dakota. J. Wildl. Manage. 36:983-987.

Myrberget, S., C. Norris, and E. Norris. 1975. Grit in Norwegian Lagopus spp. Norw. J. Zool.

23:205-212.

Nestler, R. B. 1946. Mechanical value of grit for Bobwhite Quail. J. Wildl. Manage. 10:37-42.

Norman, F. I., and R. S. Brown. 1985. Gizzard grit in some Australian waterfowl. Wildfowl

36:77-80.

Norman, F. I., and L. Mumford. 1985. Studies on the Purple Swamphen. Porphyrio porphyrio. in

Victoria. Aust. Wildl. Res. 12:263-278.

Norris, E., C. Norris, and J. B. Steen. 1975. Regulation and grinding ability of grit in the gizzard

of Norwegian Willow Ptarmigan fLagopus lagopusV Poult. Sd. 54:1839-1843.

Nys, Y., B. Sauveur, L. Lacassagne, and P. Mongin. 1976. Food, caldum and water intakes by

hens lit continuously from hatching. Br. Poult. Sd. 17:351-358.

Nystrom, K. G. K., O. Pehrsson, and D. Broman. 1991. Food of juvenile Common Eiders

(Somateria mollissima) in areas of high and low salinity. Auk 108:250-256.

Oluyemi, J. A., A. S. Arafa, and R. H. Harms. 1978. Influence of sand and grit on the

performance of turkey poults fed on diets containing two concentrations of protein. Br.

Poult. Sd. 19:169-172. 129

Owen, M. 1973. The winter feeding ecology of wigeon at Bridgwater Bay, Somerset. Ibis

115:227-243.

Owen, M., and C. J. Cadbury. 1975. The ecology and mortality of swans at the Ouse Washes,

England. Wildfowl 26:31-42.

Pank, L. F. 1976. Effects of seed and background colors on seed acceptance by birds. J. Wildl.

Manage. 40:769-774.

Passmore, M. F. 1981. Population biology of the Common Ground Dove and ecological

relationships with Mourning and White-winged Doves in south Texas. Ph.D. dissertation,

Texas A&M Univ., College Station. 109 pp.

Pendergast, B. A., and D. A. Boag. 1970. Seasonal changes in diet of Spruce Grouse in central

Alberta. J. Wildl. Manage. 34:605-611.

Peterson, S. R., and R. S. Ellarson. 1977. Food habits of Oldsquaws wintering on Lake Michigan.

Wilson BuU. 89:81-91.

Phillips, J. C., and F. C. Lincoln. 1930. American waterfowl: their present situation and the

outlook for their future. Houghton Miiflin, Boston and New York. 312 pp.

Pinowska, B. 1975. Food of female House Sparrows (Passer domesticus L.) in relation to stages of

the nesting cycle. Pol. Ecol. Stud. 1:211-225.

Pinowska, B., and K. Kra§nicki. 1985. Quantity of gastroliths and magnesium and calcium contents in the body of female House Sparrows during their egg-laying period. Zesz.

Nauk. Filii UW, 48, Biol. 10:125-130.

Player, P. V. 1971. Food and feeding habits of the Common Eider at Seafield, Edinburgh, in

winter. Wildfowl 22:100-106. Porkert, J, 1972. (On the change of grit in our grouse [Tetraonidae.]) Vestn. Cesk. Spol. Zool.

36:134-159.

Porkert, J., and N. H. Hoglund. 1984. (Control of grit content in the stomach of Tetraonides). Z.

Jagdwiss 30:81-88.

Proudfoot, F. G. 1973. Effects of feeding grit on the performance of leghorns housed in cages and

fed an all-mash laying diet. Can. J. Anim. Sd. 53:601-603.

PuUiainen, E. 1979. Grit intake of the Capercaillie. Tetrao urogallus. in the northern Finnish taipa

in autumn. Aquilo Ser. Zool. 19:45-47.

PuUiainen, E, 1984. Changes in the composition of the autumn food of Perdix perdix in west

Finland over 20 years. J. Appl. Ecol. 21:133-139.

PuUiainen, E., and J. livanainen. 1981. Winter nutrition of the WiUow Grouse (Lagopus lagopus

L.) in the extreme north of Finland. Ann. Zool. Fennici 18:263-269.

Rajala, P. 1958. (The choice of grinding stones by Capercaillie, Black Grouse, and ptarmigan in

the light of enclosure experiments.) Suomen Riista 12:89-93.

Robel, R. J., and A. R. Bisset. 1979. Effects of supplemental grit on metabolic efficiency of

bobwhites. Wildl. Soc. BuU. 7:178-181.

Roper, T.J. 1990. Responsesof domestic chicks to artificiaUy coloured insect prey: effects of

previous experience and background colour. Anim. Behav. 39: 466-473.

Roper, T. J., and S. E. Cook. 1989. Responses of chicks to brightly coloured insect prey.

Behaviour 110:276-293.

Roper, T. J., and S. Redston. 1987. Conspicuousness of distasteful prey affects the strength and

durability of one-trial avoidance learning. Anim. Behav. 35: 739-747. 131

Rowland, L. O. Jr., and D. M. Hooge. 1980. Effect of dietary sand on the performance of young

broiler chickens. Poult. Sd. 59:1907-1911.

Royama, T. 1970. Factors governing the hunting behaviour and selection of food by the Great Tit

(Parus major L.). J. Anim. Ecol. 39:619-668.

Rundle, W. D., and M. W. Sayre. 1983. Feeding ecology of migrant soras in southeastern

Missouri. J. Wildl. Manage. 47:1153-1159.

Sadler, K.C. 1961. Grit selectivity by the female pheasant during egg production. J. Wildl.

Manage. 25:339-341.

Scott, M. L., and G. F. Heuser. 1957. The value of grit for chickens and turkeys. Poult. Sd.

36:276-283.

Selden, P. A., and R. M. H. Smith. 1978. The provenance of gizzard grit from the Red Grouse

fLagopus lagopus scoticus [Latt\.]) of Bleaklow, Derbyshire. Naturalist 103:145-150.

Severin, H. C. 1933. An economic study of the food of the Ring-necked Pheasant in South

Dakota. S. Dakota Game and Fish. 252 pp.

Sharp, W. M., and H. E. McClure. 1945. The pheasant in the sandhill region of Nebraska. Pages

203-233 in W. L. McAtee, ed. The Ring-necked Pheasant and its management in North

America. Am. Wildl. Inst., New York.

Short, L. L. 1993. The lives of birds: birds of the world and their behavior. Henry Holt and Co.,

New York. 256 pp.

Sibbald, I. R., and R. S. Gowe. 1977. Effects of insoluble grit on the productive performance of

ten white leghorn strains. Br. Poult. Sd. 18:433-442.

Siegel-Causey, D. 1990. Gastroliths assist digestion in shags. Notomis 37:70-72. Siegfried, W. R. 1973. Summer food and feeding of the Ruddy Duck in Manitoba. Can. J. Zool.

51:1293-1297.

SillSn-Tullberg, B. 1985. The significance of coloration per se, independent of background, for predator avoidance of aposematic prey. Anim. Behav. 33:1382-1384.

Skead, D. M., and R. J. H. Mitchell. 1983. Grit ingested by waterfowl in relation to diet. S. Afr.

J. Wildl. Res. 13:32-34.

Slaby, M., and F. Slaby. 1977. Color preference and short-term learning by Steller's Jays. Condor

79:384-386.

Smith, H. H., and R. N. Rastall. 1911. Grit. Pages 94-99 in A.S. Leslie, ed. The grouse in health

and in disease. Smith Elder, London.

Smith, R. E. 1960. The influence of size and surface condition of grit upon the digestibility of feed

by the domestic fowl. Can. J. Anim. Sd. 40:51-56.

Smith, R. E., and T. M. Maclnt5n:e. 1959. The influence of soluble and insoluble grit upon the

digestibility of feed by the domestic fowl. Can. J. Anim. Sd. 39:164-169.

Soler, M., N. Alcala, and J. J. Soler. 1990. (Diet of the Jackdaw Corvus monedula in three areas of southern Spain.) Donana, Acta Vertebr. 17:17-48. Spallanzani, L. 1783. Experiences sur la digestion de I'homme et de differentes esp&ces d'animaux. Barthelemi Chirol, Libraire, Gendve. [Cited in Westerskov 1965.] Spitzer, G. 1972. Tahreszeitliche Aspekte der Biologie der Bartmeise (Panurus biarmicus^. T.

Omithol. 113:241-275. [Cited in Welty and Baptista 1988.]

Spray, C. J., and H. Milne. 1988. The inddence of lead poisoning among Whooper and Mute

Swans Cygnus cyngus and C. olor in Scotland. Biol. Conserv. 44:265-281.

St. Louis, V. L., and L. Breebaart. 1991. Caldum supplements in the diet of nestling Tree

Swallows near add sensitive lakes. Condor 93:286-294. 133

Stoddard, H. L. 1931. The Bobwhite Quail: its habits, preservation and increase. Charles

Scribner's Sons, New York. 559 pp.

Stokes, W. L. 1987. Dinosaur gastroliths revisited. J. Paleontol. 61:1242-1246.

Swanson, G. A., and J. C. Bartonek. 1970. Bias associated with food analysis in gizzards of Blue-

winged Teal. J. Wildl. Manage. 34:739-746.

Szymczak, M. R., and W. J. Adrian. 1978. Lead poisoning in Canada Geese in southeast

Colorado. J. Wildl. Manage. 42:229-306.

Tagami, S. 1974. On the variation of retention and form of grit in gizzard of growing chicks. Sd.

Rep. Faculty Agric., Ibaraki Univ. 22:7-13.

Tagami, S., and T. Kuchii. 1971. Effects of grit on the growth of chicks fed with rations at some

differential levels of grain size. Sd. Rep. Faculty Agric., Ibaraki Univ. 19:15-20.

Tagami, S., T. Nakaya, T. Kuchii, Y. Tarumoto, S. Tamai, and K. Kawamura. 1969. Effects of grit

on chick growth with morphological study of alimentary canal. Jap. Poult. Sd. 6:171-178.

Taylor, T, G. 1970. The provision of caldum and carbonate for lapng hens. Pages 108-117 in H.

Swan and D. Lewis, eds. Proc. Univ. Nottingham Fourth Nutr. Conf. Feed

Manufacturers. J. and A, Churchill, London.

Thomas, G. J. 1975. Ingested lead pellets in waterfowl at the Ouse Washes, England, 1968-1973.

Wildfowl 26:43-48.

Thomas, G. J., M. Owen, and P. Richards. 1977. Grit in waterfowl at the Ouse Washes, England.

Wildfowl 28:136-138.

Tindall, A. R. 1973. Gastroliths in Norwegian Grouse (Lagopus lagopus^. Acta Physiol. Scand.,

Suppl. 396:66.

Titus, H. W. 1949. The sdentific feeding of chickens. Interstate Press, Danville, 111. 253 pp. 134

Tortuero, F., and C. Centeno. 1973. Studies of the use of caldum carbonate in the feeding of

laying hens during summer months. Poult. Sd. 52:866-872.

Trost, R. E. 1981. Dynamics of grit selection and retention in captive Mallards. J. Wildl. Manage.

45:64-73.

Turner, A. K. 1982. Timing of laying by swallows (Hirundo rustical and Sand Martins (Riparia

riparia). J. Anim. Ecol. 51:29-46.

U.S. Dep. Agric. 1992. Agricultural chemical usage: 1991 field crops survey. U.S. Dep. Agric.,

Econ. Res. Serv., Washington, D.C.

Vance, D. R. 1971. Physical and chemical alterations of grit consumed by pheasants. J. Wildl.

Manage. 35:136-140.

Verbeek, N. A. M. 1967. Breeding biology and ecology of the Homed Lark in alpine tundra.

Wilson BuU. 79:208-218.

Verbeek, N. A. M. 1970. Breeding ecology of the Water Pipit. Auk 87:425-451.

Verbeek, N. A. M. 1971. Hummingbirds feeding on sand. Condor 73:112-113.

Vesey-Fitzgerald, B. S. 1946. British game. Collins, London. 240 pp.

Walter, E. D., and J. R. Aitkin. 1961. The value of soluble and insoluble grit in all-mash and

mash-grain rations for caged layers. Poult. Sd. 40:904-909.

Walton, K. C. 1984. Stomach stones in Meadow Pipits Anthus pratensis. Bird Study 31:39-42.

Ward, A. L. 1964. Foods of the Mourning Dove in eastern Colorado. J. Wildl. Manage. 28:152-

157.

Weigand, J. P. 1980. Ecology of the Hungarian Partridge in north-central Montana. Wildl.

Monogr. 74:1-106. 135

Welty, J. C, andL. Baptista. 1988. The life of birds, 4th ed. Saunders College Publ., New York.

581 pp.

West, G. C. 1967, Nutrition of Tree Sparrows during winter in central Illinois. Ecology 48:58-67.

Westerskov, K. 1965. Utilisation of grit by pheasants in New Zealand. New Zealand Dep.

Internal Affairs Wildl. Publ. No. 65. 31pp.

Wetmore, A. 1919. Lead poisoning in waterfowl. U.S. Dep. Agric. Bull. 793. 12 pp.

White, M., and S. W. Harris. 1966. Winter occurrence, foods, and habitat use of snipe in

northwest California. J. Wildl. Manage. 30:23-34.

Wiley, J. W., and B. N. Wiley. 1979. The biology of the White-crowned Pigeon. Wildl. Monogr.

64:1-54.

Wilhelm, G. J. 1982. (Resultsof faeces analysis of Capercaillie in the Vosges). Z. Jagdwiss.

28:162-169.

Wilson, J. E. 1959. The status of the Hungarian Partridge in New York. Kingbird 9:54-57.

Wood-Gush, D. G. M., and M. R. Kare. 1966. The behaviour of caldum-deficient chickens. Br.

Poult. Sd. 7:285-290.

Yamatani, Y., and I. Otani. 1969. Fundamental studies on the digestion in the domestic fowl. V.

Effect of grit on the chemical composition of gizzard. J. Faculty Fish. Anim. Husb,

Hiroshima Univ. 8:99-104.

Young, D. J. 1967. Loess deposits of the west coast of the South Island, New Zealand. New

Zealand J. Geol. Geophys. 10:647-658.

Zimmerman, J. L. 1963. The bioenergetics of the Dickdssel. Spiza americana. Ph.D. dissertation,

Univ. Dl., Urbana. 142 pp. 136

Ziswiler, V., and D. S. Famer. 1972. Digestion and the digestive system. Pages 343-430 in D. S.

Famer, J. R. King, and K. C. Parkes, eds. Avian biology, vol. 2. Academic Press, New

York. Table 1. Wild birds using mainly quartz as grit.

Spedes Source

12 spp. ducks Anderson 1959

12 spp, waterfowl Thomas et al. 1977

11 spp. waterfowl Norman and Brown 1985

Spur-winged Goose Halse 1983

Ring-necked Pheasant Dalke 1938

Ring-necked Pheasant Korschgen 1964

Ring-necked Pheasant, Gray Partridge, ptarmigan Smith and Rastall 1911

Willow Ptarmigan, Rock Ptarmigan Kolderup 1925®, M5n:berget et al. 1975

Red Grouse Smith and Rastall 1911, Selden and Smitti 1978

White-tailed Ptarmigan May and Braun 1973

Ruffed Grouse Bump et al. 1947

Purple Swamphen Norman and Mumford 1985

Eurasian Woodcock Koubekl986 Common Snipe N. America Tuckl972

7 spp. wading birds Norway liQeld 1983, Moksnes 1988

House Sparrow, Eurasian Tree Sparrow Germany Kefl 1973

Meadow Pipit Norway Higvar and 0stbye 1976 Water Pipit Wyoming Verbeekl970

® Gted in Selden and Smidi 1978. 139

Table 2. Duration of grit retention in gizzards of birds.

Spedes Duration of Retention Source

Mallard 60 days Godin 1967

Mallard 7.5 months Anderson 1959

Ring-necked Pheasant 6 weeks GersteU1942

Northern Bobwhite 6 weeks Errington 1931

Northern Bobwhite 5 months Nesder 1946

Northern Bobwhite 9 months Robel and Bisset 1979

Domestic chicken 8 months Buckner et al. 1923®

Domestic chicken 11 months Walter and Aitken 1961

Domestic chicken 1 year Kraupp 1924

®Cited in Buckner et al. 1926. 140

Table 3. Items found in gizzards of wild birds and considered grit substitutes by original authors.

Grit substitute Species Location Source

Hard seeds 10 spp. waterfowl England Thomas et al. 1977

4 spp. waterfowl South Africa Skead & MitcheU 1983

5 gallinaceous spp. U.S. Beer & Tidyman 1942

Kalij Pheasant Hawaii Lewin & Lewin 1984

Ring-necked Pheasant Nebraska Sharp & McClure 1945

Ring-necked Pheasant New Zealand Westerskov 1965

Red Grouse British Isles Smith & Rastall 1911

Capercaillie unspecified Teplov 1947®

Ruffed Grouse New York Bump et al. 1947

Northern Bobwhite U.S. Stoddard 1931

Northern Bobwhite U.S. Nestiier 1946

Purple Swamphen New Zealand Carroll 1966

Purple Swamphen Australia Norman & Mumford 1985

"Pigeons, doves, & unspecified Meinertzhagen 1954

game birds"

Mourning Dove N. America Lewis 1993

Red-winged Blackbird South Dakota Mott et al. 1972 141

Shells/fragments 11 spp. waterfowl Australia Norman & Brown 1985

10 spp. waterfowl England Thomas et al. 1977

5 spp. ducks Illinois Anderson 1959

Eurasian Dipper, unspecified Meinertzhagen 1954

Shelduck, European Starling

Ring-necked Pheasant Misssouri Korschgen 1964

Ring-necked Pheasant New Zealand Westerskov 1965

Common Snipe N. America Tuck 1972

5 spp. waders Norway Lifjeldl983

Mourning Dove Iowa McClure 1941

Mourning Dove Colorado Ward 1964

Great Tit England, Japan Royama 1970

Meadow Pipit Norway H&gvar & 0stbye 1976 Red-winged Blackbird South Dakota Mott et al. 1972

Insect parts Common Pauraque C. & S. America Jenkinson & Mengel 1970

Red-winged Blackbird Manitoba Bird & Smith 1964

Red-winged Blackbird South Dakota Mott et al. 1972

Lead shot Black-bellied Texas Bolen & Forsyth 1967

Whistling-duck

13 spp. waterfowl England Thomas 1975, Thomas et

al. 1977 142

Mallard, Northern England Meinertzhagen 1964

Shoveler

Australian Black Duck Australia Norman & Brown 1985

Ring-necked Pheasant Nebraska Sharp & McClure 1945

Ring-necked Pheasant New Zealand Westerskov 1965

Purple Swamphen Australia Norman & Mumford 1985

Fossils 11 spp. waterfowl Australia Norman & Brown 1985

17 spp. ducks Illinois Anderson 1959

Glass fragments Black-bellied Texas Bolen & Forsyth 1967

Whistling-duck

11 spp. waterfowl Australia Norman & Brown 1985

Ring-necked Pheasant Nebraska Sharp & McClure 1945

Ring-necked Pheasant New Zealand Westerskov 1965

Mourning Dove Iowa McClure 1941

Purple Martin Texas Brown 1976*'

Coral, wood, bones, 17 spp. ducks Illinois Anderson 1959

teeth

Teeth Water Pipit Wyoming Verbeek 1970

®Cited in Pulliainen 1979. ''Birds were observed consuming glass and grit. Appendix 1. Sources of infonnation on grit use by wild birds.

Grit Grit Grit Grit Grit Taxon Location Sex® Age Season*^ amount^ size® shape^ color^ comp.^'S Source

Double-crested Gulf of N Sp R X - - Minerl962 Cormorant California

Black-bellied Texas M+F J+A Sp+Su W SC - - - Bolen& Forsyth 1%7 Whistling-duck

Ruddy Duck Manitoba M,F J,A Su V,W SC - - - Siegfriedl973

Blue-hilled Duck Australia F A F W SC - - X Norman & Brown 1985

Musk Duck Australia M,F A F W SC - - X Norman & Brown 1985

Freckled Duck Australia M,F A F W SC - - X Norman & Brown 1985

Mute Swan England W W SC - - - Owen & Cadbury 1975

Mute Swan England F+W W SC - X X Thomas etal. 1977

Mutei Swan Scofland W - - - - Spray & Milne 1988

Whooper Swan Scotland W - - - - Spray & Milne 1988

Bewick's Swan England W W SC - - - Owen & Cadbury 1975

Bewick's Swan England F+W W SC - X X Thomas etal. 1977 Emperor Goose Alaska - J+A Sp+Su Eisenhauer & fCirlq>atrick 1977

Canada Goose Wisconsin - J+A F Craven & Hunt 1984

Australian Shelduck Australia M,F A F Norman & Brown 1985

Spur-winged Goose S. Africa M,F J,A Su Halse 1983

Wood Duck Illinois - - F Anderson 1959

Maned Goose Australia M,F A F Norman & Brown 1985

Eurasian Wigeon England - - F+W Owen 1973

Eurasian Wigeon Eng^nd M,F - F+W Thomas et al. 1977

American Wigeon Illinois - - F Anderson 1959

Gadwall Illinois - - F Anderson 1959

Gadwall England - - F+W Thomas et al. 1977

Green-winged Teal Illinois - - F Anderson 1959

Green-winged Teal England - - F+W Thomas et al. 1977

Cape Teal S. Africa M+F A Skead & Mitchell 1983

Grey Teal Australia M,F A F Norman & Brown 1985 Chestnut Teal Australia M,F SC - - X Norman & Brown 1985

Mallard Illinois R X - X Anderson 1959

Mallard England SC - X X Thomas et al. 1977

Yellow-billed Duck S. Africa M+F SC - X X Skead&MitcheU1983

Australian black Australia M,F SC - - X Norman & Brown 1985 Duck

Northern Pintail Illinois R X - X Anderson 1959

Northern Pintail England SC - X X Thomas et al. 1977

Red-billed Teal S. Africa M+F SC - X X Skead& Mitchell 1983

Blue-winged Teal Illinois R X - X Anderson 1959

Cape Shoveler S. Africa M+F SC - X X Skead&Mitchem983

Australian Shoveler Australia M,F SC - - X Norman & Brown 1985

Northern Shoveler Illinois R X - X Anderson 1959

Northern Shoveler England SC - X X Thomas et al. 1977

Pink-eared Duck Australia M,F SC - - X Norman & Brown 1985

Southern Pochard S. Africa M+F SC - X X Skead & Mitchell 1983 Common Pochard Eng^nd F+W Thomas et al. 1977

Canvasback Illinois F Anderson 1959

Canvasback Manitoba M,F J, A Su Bartonek 1%9

Redhead Illinois Anderson 1959

Redhead Manitoba M,F J,A Su Bartonek 1%9

Ring-necked Duck Illinois F Anderson 1959

Australian White-eye Australia F A F Norman & Brown 1985

Tufted Duck England F+W Thomas et al. 1977

Lesser Scaup Illinois F Anderson 1959

Lesser Scaup Manitoba M,F J,A Su Bartonek 1969

Common Eider Firtti of Forth M+F J+A W Player 1971

Common Eider Sweden - J F Nystrom et al. 1991

Oldsquaw Lake Sp+W Peterson & Ellarson 1977 Michigan

White-faced Ibis Texas Su Hall & Fisher 1985

Gray Partridge Washington Beer & Tidyman 1942 Gray Partridge Montana J,A Sp,Su, PV,0 - - - - Weigandl980 F,W

Gray Partridge Finland W,0 - - - - PuUiainen 1984

Kalij Pheasant Hawaii Sp+Su+ N R - - - Lewin & Lewin 1984 W

Ring-necked Pheasant Utah M,F J,A Sp/Su, N,0 - - - - Cottainl929 F,W

Ring-necked Pheasant S. Dakota - - Sp,Su, N,V,0 - - - X Severinl933 F,W

Ring-necked Pheasant Michigan J,A Sp,Su, W M - - X Dalkel938 F,W

Ring-necked Pheasant Washington V,0 - - - - Beer & Tidyman 1942

Ring-necked Pheasant Nebraska Sp+Su+ N,V,W - - - - Sharp & McQure 1945 F+W

Ring-necked Pheasant California J,A Sp+Su+ V,0 - - - - Ferrel et al. 1949 F+W

Ring-necked Pheasant Illinois J Su,F,W W M - - X Harper 1963

Ring-necked Pheasant Illinois A Sp,Su, W,0 - - - X Harper 1964 F,W Ring-necked Pheasant Illinois M,F J, A Sp,Su, W X Harper & Labislgr 1964 F,W

Ring-necked Pheasant Missouri M,F J, A Sp,Su, W X Korschgen 1964 W

Ring-necked Pheasant New M,F J,A Sp,Su, N,V,W,0 R,S X Westerskov 1965 Zealand F,W C,M

Ring-necked Pheasant Minnesota M,F J+A Sp,Su, W X Kopischke 1966 F,W

Ring-necked Pheasant Minnesota & F A Sp+Su W SC X Kopischke & Nelson 1%6 S. Dakota

Spruce Grouse Montana PV,0 Jonkel & Greer 1963

Spruce Grouse Alaska Sp,Su,F O Ellison 1966

Spruce Grouse Alaska W R,M Hoskin et aL 1970

Spruce Grouse Alberta M+F J, A Sp,Su, V,W,0 Pendergast& Boag 1970 F,W

Franklin's Grouse Beer & Tidyman 1942 (Spruce Grouse)

Blue Grouse Washington Sp+Su+ V,0 Beer & Tidyman 1942 F

Blue Grouse Washington M+F J+A F V,0 - - - - Boag 1963 Blue Grouse Alaska - - - W R,M - - - Hoskin et al. 1970

Willow Ptarmigan Alaska W R,M - - - Hoskin etal. 1970

Willow Ptarmigan Norway - - Sp,F,W N SC - - - Norris et al. 1975

Willow Ptarmigan Norway - ],A Su,F,W N,W,0 - X - X Kolderup 1925^

Willow Ptarmigan Norway M,F J,A Sp,F,W N,W,0 SC X - X Myrberget etal. 1975

Willow Ptarmigan Finland M+F - W O - - - - Pulliainen & livanainen 1981

Red Grouse British Isles - J,A N,W - X - X Smith & Rastall 1911

Red Grouse England - - F SC, XXX Selden & Smitti 1978 M

Rock Ptarmigan Alaska - - Sp+Su+ W R,M X - . Hoskin etal. 1970 F+W

Rock Ptarmigan Norway - J,A W N,W SC X - X Myrberget etal. 1975

White-tailed Ptarmigan N.A. - - - O - - - - Beer & Tidyman 1942

White-tailed Ptarmigan Alaska W R,M - - - Hoskin et al. 1970

White-tailed Ptarmigan Colorado M,F A Sp,Su, W,0 SC, X - X May & Braun 1973 F,W M

Capercaillie Finland M,F J,A F,W N,W SC - - - Pulliainen 1979 Ruffed Grouse Washington Su+F+ V,0 - - - Beer & Tid)anan 1942 & Idaho W

Ruffed Grouse New York J, A Sp,Su, PV R X X - Bump etal. 1947 F,W

Ruffed Grouse Alaska W R,M - - - Hoskin etal. 1970

California Quail N.A. J+A Su V,0 - - - - Beer & Tidyman 1942

California Quail Washington A Sp,Su, PV - - - - Crispens et al. 1960 F,W

Northern Bobwhite N.A. PV - - - - Stoddard 1931

Northern Bobwhite Tennessee & V,0 - - - - Beer & Tidyman 1942 Washington

Purple Swamphen New Sp,Su, W,0 R - - - CarroUl%6 Zealand F,W

Purple Swamphen Australia M,F Sp,Su, W,PV SC - - X Norman & Mumford 1985 F,W

Common Moorhen England F+W W SC - X X Thomas et al. 1977

Eurasian Coot England F+W W SC - X X Thomas et al. 1977

Eurasian Woodcock Czech Sp N,W,0 R,M - - X Koubekl986 Republic Common Snipe California W PV,0 White and Harris 1966

Common Snipe Canada Sp,F PV,0 Tuck 1972

Long-billed Dowitcher Texas Su Hall & Fisher 1985

Western Sandpiper Texas Su Hall & Fisher 1985 litde Stint Norway F w,o Lifjeld 1983

Temminck's Stint Norway M+F Su N,W,0 Moksnes 1988

Least Sandpiper Texas Su Hall & Fisher 1985

Pectoral Sandpiper Texas Su HaU & Fisher 1985

Dunlin Sweden PV,0 Bengtson & Svensson 1968

Dunlin Norway F w,o Lifjeld 1983

Curlew Sandpiper Norway F w,o Lifjeld 1983

Stilt Sandpiper Texas Su HaU & Fisher 1985

Ruff Norway M,F w,o Lii5eldl983 Wilson's Phalarope N. Dakota M,F Sp N R,M Garcher & Carroll 1991

Black-necked Stilt Texas Su SC, Han & Fisher 1985 M

Ringed Plover Norway F W,0 MD X Lifjeld 1983

Ringed Plover Norway M+F Su N,W,0 X Moksnes 1988

White-crowned Pigeon Puerto Rico N, Su,F V,PV,0 Wiley & Wiley 1979 J+A

Mourning Dove Missouri - Sp+Su+ N,V,PV, Chambers 1963 F+W O

Mourning Dove Colorado - Sp,Su,F V,PV,0 Ward 1964

Caprimulgids: 9 N.A.+ N,0 R Jenkinson & Mengel 1970 species C.A.+S.A.

Jackdaw Spain Sp,Su, PV M Soler et al. 1990 F,W

American Crow Tennessee W v,o Beer & Tidyman 1942

House Wren Manitoba N,A Su N,W,0 SC X Mayoh & Zach 1986

Tree Swallow Manitoba N,A Su N,W,0 SC X Mayoh & Zach 1986

Bam Swallow Washington N N,0 SC X Barrentine 1980 Marsh Tit England Sp,Su, O - - - - Bettsl955 F,W

Coal Tit England - Sp,Su, O - - - - Bettsl955 F,W

Great Tit England Sp,Su, O - - - - Betts 1955 F,W

Blue Tit England Sp,Su, O - - - - Betts 1955 F,W

Homed Lark Wyoming N,A Su W - - - - Verbeek 1%7

House Sparrow Germany F+W W R - - X Keill973

House Sparrow Poland F A Sp+Su+ W,0 - - - - Pinowska 1975 W

House Sparrow Poland F A Sp N,W - - - X Pinowska & Krasnicki 1985

House Sparrow Iowa M,F J+A Sp+Su, N,0 M X X - Gionfriddo & Best 1995 F+W

Spanish Sparrow Spain M,F NJ, Sp,Su, N,W,0 R,M - - - Alonso 1985 A F,W

Eurasian Tree Sparrow Germany - - F+W W R - - X Keill973

Meadow Pipit Norway N,A Su N,W,0 - - - X Hagvar&0stt)yel976 Meadow Pipit N. Wales J,A Sp+Su+ N,W,0 X Walton 1984 F

Water Pipit Wyoming N,A Su W X Verbeekl970

Dunnock England A Sp,Su, N M Bishton 1986 F,W

Red-billed Quelea Africa A Su O X Jones 1976

Brambling Norway N,A Sp+Su N,0 EM X Hogstadl988

American Tree Illinois W w,o West 1967 Sparrow

Red-winged Blackbird Manitoba - - Su,F PV Bird and Smitti 1964

Red-winged Blacklnrd S. Dakota M+F Sp,Su P/V,0 Mott et al. 1972

Great-tailed Grackle Texas - N Sp Davis & Arnold 1972

® Sexes: M,F = data for sexes reported separately; M+F = data for sexes combined; dash = sexes not distinguished. Age categories: N = nesUing, J = juvenile, and A = adult J,A = data for juveniles and adults reported separately; J+A = data for juveniles and adults combined. Dash = ages not given. Season; Sp = spring, Su = summer, F = fall, and W = winter. Data for seasons separated by commas were reported separately; data for seasons separated by "+" were combined. Dash = season(s) not given. Grit amount reported as: N = number, V = volume, W = weight, PV = proportion of the total volume of stomach contents, and O = occurrence (the proportion of sampled birds in which grit particles were found). Dash = no information given. ® Grit size reported as: R = range, SC = size categories, M = mean, EM = estimated mean, and MD = median. Dash = no information given. ^ X = information given; dash = no information given. 8 Grit composition (e.g., minerals). Dash = no information given. 156

Appendix 2. Scientific names of avian species/subspedes whose common names appear in text, tables or Appendix 1,

Common Name Sdentific Name

Ostrich Struthio camelus

Double-crested Cormorant Phalacrocorax auritus

White-faced Ibis Plegadis chihi

Black-bellied Whistling-duck Dendrocygna autumnalis

Ruddy Duck Oxyura jamaicensis

Blue-billed Duck Oxyura australis

Musk Duck Biziura lobata

Freckled Duck Stictonetta naevosa

Mute Swan Cvgnus olor

Whooper Swan Cvgnus cygnus

Bewick's Swan Cygnus columbianus bewickii

Lesser Snow Goose Anser caerulescens caerulescens

Emperor Goose Anser canagicus

Canada Goose Branta canadensis

Australian Shelduck Tadoma tadomoides

Shelduck Tadoma tadoma

Spur-winged Goose Plectropterus gambensis

Wood Duck Aix sponsa 157

Maned Goose Chenonetta jubata

Eurasian Wigeon Anas penelope

American Wigeon Anas americana

Gadwall Anas strepera

Green-winged Teal Anas crecca

Cape Teal Anas capensis

Grey Teal Anas gibberifrons

Chestnut Teal Anas castanea

Mallard Anas platyrhynchos

Yellow-billed Duck Anas undulata

Australian Black Duck Anas superdliosa

Northern Pintail Anas acuta

Red-billed Teal Anas erythrorhyncha

Blue-winged Teal Anas discors

Cape Shoveler Anas smithii

Australian Shoveler Anas rhynchotis

Northern Shoveler Anas clypeata

Pink-eared Duck Malacorhynchus membranaceous

Southern Pochard Netta erythrophthalma

Common Pochard Aythya ferina

Canvasback Aythya valisineria

Redhead Aythya americana

Ring-necked Duck Aythya collaris 158

Australian White-eye Aythya australis

Tufted Duck Aythya fuligula

Lesser Scaup Aythya affinis

Common Eider Somateria moUissima

Oldsquaw Clangula hyemalis

Gray Partridge Perdix perdix

Japanese Quail Cotumix japonica

Domestic chicken Gallus domesticus

Kalij Pheasant Lophura leucomelanos

Ring-necked Pheasant Phasianus colchicus

Spruce Grouse Dendragapus canadensis

Blue Grouse Dendragapus obscurus

Willow Ptarmigan Lagopus lagopus

Red Grouse Lagopus lagopus scoticus

Rock Ptarmigan Lagopus mutus

White-tailed Ptarmigan Lagopus leucurus

Capercaillie Tetrao urogallus

Ruffed Grouse Bonasa umbellus

Wild Turkey Meleagris gallopavo

California Quail Callipepla califomica

Northern Bobwhite Colinus virginianus

Purple Swamphen Porphyrio porphyrio

Common Moorhen Gallinula chloropus 159

Eurasian Coot Fulica atra

Eurasian Woodcock Scolopax rusticola

Common Snipe Gallinago gallinago

Long-billed Dowitcher Limnodromus scolopaceus

Western Sandpiper Calidris mauri

Little Stint Calidris minuta

Temminck's Stint Calidris temminckii

Least Sandpiper Calidris minutilla

Pectoral Sandpiper Calidris melanotos

Dunlin Calidris alpina

Curlew Sandpiper Calidris ferruginea

Stilt Sandpiper Micropalama himantopus

Ruff Philomachus pugnax

Wilson's Phalarope Steganopus tricolor

Black-necked Stilt Himantopus mexicanus

Ringed Plover Charadrius hiaticula

Wood Pigeon Columba palumbus

White-crowned Pigeon Columba leucocephala

Band-tailed Pigeon Columba fasciata

Mourning Dove Zenaidura macroura

Common Pauraque Nyctidromus albicollis

Anna's Hummingbird Calypte anna

Jackdaw Corvus monedula 160

American Crow Corvus brachyrhynchos

Eurasian Dipper Cindus cinclus

European Starling Stumus vulgaris

House Wren Troglodytes aedon

Tree Swallow Tachydneta bicolor

Purple Martin Progne subis

Bank Swallow Riparia riparia

Bam Swallow Himndo rustica

Bearded Tit Panurus biarmicus

Marsh Tit Parus palustris

Coal Tit Pams ater

Great Tit Pams major

Blue Tit Pams caemleus

Homed Lark Eremophila alpestris

House Sparrow Passer domesticus

Spanish Sparrow Passer hispaniolensis

Eurasian Tree Sparrow Passer montanus

Meadow Pipit Anthus pratensis

Water Pipit Antftus spinoletta

Dunnock Pmnella modularis

Red-billed Quelea Quelea quelea

Brambling Fringilla montifringilla

Eurasian Siskin Carduelis spinus 161

American Tree Sparrow Spizella arborea

Red-winged Blackbird Agelaius phoeniceus

Great-tailed Grackle Ouiscalus mexicanus 162

CHAPTER Vffl. GENEEiAL CONCLUSIONS

The saline flushing technique is a highly efficient means of removing all material from the gizzards of granivorous birds. The method enables avian researchers to collect and analyze the food items and grit consumed by birds without having to kill the birds. It has a low (8%) mortality rate and may be used either in the field to sample the gizzard contents of free-ranging birds or in the laboratory in connection with research experiments. Because of its nonlethal nature, the saline flushing technique permits repeated sampling of the food habits and grit consumption of individual birds.

The effects of diet and grit size on grit use by House Sparrows were evaluated by examining the gizzard contents of free-ranging birds and by conducting a series of aviary experiments with captive birds. Free-ranging House Sparrows used more grit during the warm months of the year when they often consumed hard-bodied insects (mostly coleopterans) in addition to the seeds that made up the majority of their diet. Males and females did not differ in mean grit size or number. In aviary experiments, gizzards of House Sparrows using small grit consistently contained more (an average of 5 times as many) particles than those of birds using large grit. No consistent differences in grit use were associated with differences in diets of captive

House Sparrows. Grit turnover rates in gizzards of experimental birds were high: generally, most

(more than 75%) grit particles were replaced in gizzards within 5 days. Diet and grit size both exert important effects on grit use by House Sparrows. The effects of diet are probably even more pronounced in avian species whose diets undergo greater seasonal shifts in the proportion of hard, coarse materials. 163

Aviary experiments with House Sparrows and Northern Bobwhites evaluated the influence of grit surface texture and shape on grit selection. The two species of experimental birds differed in prior experience with grit and in body size, and they represent different avian orders. Despite these differences, however, the responses of House Sparrows and Northern Bobwhites were very similar in the experiments. Both species expressed a clear preference for angular/oblong rattier than rounded/spherical grit when given a mixture of the two grit t5rpes. Additional experiments were conducted with captive House Sparrows to determine the influence of grit surface texture and shape on retention of grit particles in the gizzard. The results of these retention experiments suggest that surface texture and shape do not affect the retention of individual grit particles.

Selection of grit particles by birds, on the other hand, does seem to be influenced by the surface texture and shape of the grit they encounter.

The effects of grit color on avian grit selection were investigated in a series of aviary experiments with House Sparrows and Northern Bobwhites. Birds were offered a grit mixture consisting of equal amounts of 8 colors (red, brown, yellow, green, blue, black, white, clear) of particles, on either a light-brown or a dark-brown soil background. After 7 days, in gizzards of both House Sparrows and Northern Bobwhites, yellow, green, and white particles represented the greatest proportions of colored grit. Blue and black grit received relatively little use by birds. Soil background color had only a slight influence on grit color selection, and only in House Sparrows.

The influence of food color on grit color selection was examined by repeating the experiments (on dark soil only), using birds maintained on food dyed to match 3 of the 8 grit colors (red, yellow, blue). House Sparrows preferred brown, yellow, and white grit, and Northern Bobwhites preferred yellow and green grit, regardless of food color. Black grit again received little use by both avian species. Food color affected grit color selection but was not associated with substantive 164 differences in the preference rankings of the 8 grit colors. Grit color use did not differ between males and females in any of the experiments. These results indicate that particle color can be a major determinant of avian responses to grit.

Grit preferences of birds should be considered when evaluating avian risks from granular pesticides. The degree of overlap between the physical characteristics of pesticide granules and those of grit particles naturally ingested by birds can be used to evaluate the probability that birds will consume pestidde granules as grit. The greater the overlap, the greater the likelihood of pestidde granule ingestion. Of the variables examined in the research reported in this dissertation, particle color shows the most promise as a characteristic that can be manipulated to reduce avian mortality resulting from the ingestion of pestidde granules as grit.

A comprehensive review and s}mthesis of the available literature on avian grit use determined that grit is ingested and retained in the gizzards of most spedes of birds that eat plant parts and many that eat insects. Most research on avian grit use has focused on upland game birds, waterfowl, and poultry. Grit aids in the mechanical grinding of coarse, hard foods in the gizzard. Sometimes it also provides critical nutrients such as caldum. Characteristics of grit that influence its use by birds indude particle size, shape, color, and composition. The amounts of grit in birds' gizzards vary greatly and are influenced by bird age, diet, nutritional and reproductive status, and by the characteristics of the grit particles. Although most grit particles probably pass

through the digestive tract in a few hours, some may be retained in the gizzard for many months.

The mechanism of retention, and its degree of selectivity, are unknown. Evidence suggests that

particle size, shape, surface texture, and composition, in addition to grit consumption rate, may

affect particle retention. In place of grit, other non-food items are sometimes consumed and then

retained in the gizzard, where they may serve as grinding agents and, in some instances, they may 165 provide supplementary nutrients. Grit use may not be necessary for the survival of birds, but it is an important dietary component for many birds through its nutritional benefits. 166

ACKNOWLEDGMENTS

I thank Louis B. Best, my major professor, for his guidance, encouragement, and friendship throughout this study. His contagious enthusiasm never wavered, and he was never too busy to lend assistance whenever it was needed. I will always be grateful for his support and tutelage. I also thank James J. Dinsmore, Erwin E. Klaas, Jerry L. Sell, and Kennetii C. Shaw for serving on my graduate committee and providing guidance and support throughout the study.

Bret Giesler worked tirelessly as laboratory and field technician from the first to the last day of this research, and his good humor, enthusiasm for the work, and friendship greatly improved the workplace atmosphere. I am also grateful to the many friends whose thoughtful suggestions and discussions helped immeasurably over the years. These include Bret Giesler, Mary Crowe

Mitchell, Larry Igl, Ken Petersen, Gary Zenitsky, Dan Varland, Mark Wallace, and Kathy

Andersen. Finally, I thank my wife, Julie, for her many years of encouragement and limitless patience, and for the hundreds of hours she spent helping us at the aviaries and in the lab.