This dissertation has been G2—2131 microfilmed exactly as received
DIELERY, Dean George, 1928- FOOD HABITS OF SAVANNAH AND GRASSHOPPER SPARROWS IN RELATION TO FOODS AVAILABLE.
The Ohio State University, Ph.D., 19G1 Zoology
University Microfilms, Inc., Ann Arbor, Michigan FOOD HABITS OF SAVANNAH AND GRASSHOPPER
SPARROWS IN RELATION TO FOODS AVAILABLE
DISSERTATION
Praaantad in Partial Fulfillaant of tha Raquiraaanta for tha Dagraa Doctor of Fhiloaophy in tha Oraduata School of Tha Ohio Stata Univaraitj
By
DEAN GEOROE DILLERYt B. Sc., M. Sc.
Tha Ohio Stata UniTaraity 19*1
Approvad by
Fiaar Dapartaant*"bf Zoology and Entoaology ACKNOWLEDGMENTS
I wish to acknowledge and thank Dr* D. J. Borror for his help and advice and particularly for the nany suggestions which he offered. I also wish to acknowledge the assistance of the
United States Fish and Wildlife Service in providing the contents of l*t2 sparrow stonachs for ay exaaination.
ii CONTENTS
Pago
INTRODUCTION...... 1
METHODS ...... 4
Study i r t u ...... ^
Bird Collections ...... 5
Insect Collections ...... 9
Observations ...... 11
RESULTS...... 12
General Observations ...... 12
Weight and Caecal Length...... 12
Parasites and Abnormalities ...... 12
Digestive Processes ...... 13
Feeding of Toung...... 14
Foraging Behavior...... 14
Materials Eaten...... 16
Total Food Consumption...... 16
Size of Materials Eaten ...... 23
Intraspecific Variation ...... 23
Interspecific Comparisons ...... 32
DISCUSSION...... 43
SUMMARY ...... 49
BIBLIOGRAPHY...... 51
AUTOBIOGRAPHY ...... 57
iii TABLES
Table Page
1. Number of Sparrows Utilized in this Study ...... 7
2. Comparison of Sweep Samples with Observations in a Hay
F i e l d ...... 11
3. Bird Weights (in g r a m s ) ...... 12
4. Food Materials Found in 162 Savannah Sparrows ..... 17
5» Food Materials Found in 91 Grasshopper Sparrows .... 20
6. Materials Eaten by Savannah and Grasshopper SparrowB. . 23
7. Comparison of Orthoptera per Bird with Orthoptera per
Sweep in Savannah Sparrows...... 26
8. Numbers of Food Items of 11 Savannah Sparrows Taken
from a Hay Field on July 13* 1961, Calhoun Co.,
Michigan...... 28
9- Comparison of Orthoptera per Bird with Orthoptera per
Sweep in Grasshopper Sparrows...... 29
10. Comparison of Animals per Bird with Animals per Sweep
in Grasshopper Sparrows from Two F i e l d s ...... 31
11. Numbers of Food Items of Four Adult Grasshopper
Sparrows Taken from a Pasture on July 4, 1961, Marion
Co., Michigan ...... 32
12. Comparison of Animals Eaten by Savannah and Grasshopper
Sparrows in Three Fields in Marion Co., Ohio...... 33
iv FIGURES
Figure Page
1. Per cent of animal food in the diet of 162 savannah
sparrows; remainder is plant food. (Based on volume.). 2k
2. Per cent of animal food in the diet of 90 grasshopper
sparrows; remainder is plant food. (Baaed on volume.). 2k
3. Number of Orthoptera per bird eaten by savannah and
grasshopper sparrows......
Number of Homoptera per bird eaten by savannah and
grasshopper sparrows...... 37
3. Number of Cercopidae per bird eaten by savannah and
grasshopper sparrows...... 38
6. Number of Coleoptera per bird eaten by savannah and
grasshopper sparrows...... 39
7. Number of Curculionidae per bird eaten by savannah and
grasshopper sparrows...... kO
8. Number of Hemiptera and larvae per bird eaten by
savannah and grasshopper sparrows...... kl
9. Number of Diptera, Hymenoptera, and Araneida per bird
eaten by savannah and grasshopper sparrows...... ^2 INTRODUCTION
Many studies have been made of the food habits of birds, but sost of thea have been descriptive in nature and have not been concerned with ho* birds select their food. Several general food habit studies involving sparrows were made around the turn of the century, but these were mainly aimed at establishing the relation of the birds to agriculture (Beal and McAtee, 1912; Jones, 1913;
Judd, 1901, 1902; Warren, 1890; Weed, 1898; Weed and Dearborn,
1903)* Sparrows can be considered beneficial in their food habits, since among their most important food items are weed seeds, caterpillars, and grasshoppers. Little attempt was made to see whether the birds were selective in their feeding. Judd
(1897) experimented to a limited extent with the catbird (Dume- tella carolinensla) by offering it certain food items to see which it would eat. He decided that the catbird did show prefer ences. McAtee (1932) utilized figures on the food habits of all birds in comparison with calculated total numbers of animals available in his arguments against the effectiveness of protec tive adaptations in animals, but no actual counts of animals eaten in a given habitat were compared with the animals available in that habitat.
There have also been some recent papers which discuss the food habits of sparrows, either listing the foods eaten (Hyde,
1939; Knowlton, 1950) or discussing some aspect of feeding behav ior (Walkinshaw, 1 9 ^ , 19^5)* None of these papers attempt to
1 utilise field data to determine whether birds show any selectiv
ity in their diets.
The food preferences of a species could be one of the fac
tors contributing to habitat selection or a consequence of habi
tat selection. I compared stomach contents with insect material collected at the same time in the same fields to determine whether sparrows exhibit any selectivity in their feeding or whether they merely take foods in the approximate proportions in which they occur in the fields. The former would indicate that food is a factor contributing to local distribution, the latter that it is probably only a consequence of distribution. Collec tions were made during the summers of 1959* I960, and 1961. At first several species of sparrows were collected, but the work was finally limited to two species. The savannah sparrow, Pas- serculus aandwichensis (Wilson), was fairly common in some areas and occurred in fields in which the insect life could be easily sampled. The grasshopper sparrow, Ammodramus savannarum Maynard, was often found in the same fields as the savannah sparrow though never in such large numbers.
Recently several authors have studied or at least discussed the availability of food items. Quay (195^), in a study of the winter feeding habits of the savannah sparrow, discussed the plant foods available and their possible relationship to bird distribution. He Indicated that there is probably a positive correlation. Salt (1957) compared foraging microhabitats and food preferences among fox sparrows (Passerella iliaoa). song 5
sparrows (Melospisa melodia), and Lincoln's sparrows (Melospiza
lineolnii? in Wyoming. He found that each species forages in a
different microhabitat and has different food preferences.
Some work has been done on the feeding selectivity of game
birds and a few other species. Hawkins (1937)* working with four
gallinaceous species, found certain preferences in the plant
foods selected. Stoddard (1931) decided that the amount of dif
ferent foods eaten by bobwhite quail (Collnus virginianus) was correlated with availability except in the case of legumes.
Bookhout (1958), on the other had, working with bobwhite quail in southern Illinois, found that it shows distinct preferences in
the selection of plant foods. Ticehurst (19^0) in England found representatives of several orders of birds that showed prefer ences between two foods, both of which entered their normal diet.
Stenger (1958) found that the ovenbird (Seiurus aurocapillus) picks its animal food in direct correlation with abundance of that food in the particular microhabitat in which the bird feeds.
In this study I have found that savannah and grasshopper sparrows are apparently guided in their selection of animal food by the size, numbers, and speed of their prey. METHODS
Study Areas
Sparrows were collected during the summers of 1959 and i960 in three general areas in Ohio and during the summer of 19&1 in several areas in Michigan and Ohio. Michigan collections were made in Calhoun, Jackson, and Washtenaw counties in the south central part of the state. Ohio collections were made in Dela ware, Marion, and Wyandot counties in the northwest central part of the state. A total of 22 fields was utilized for collecting, and the vegetation in some of the fields was changed between collection periods.
Most savannah sparrows were found in either hay fields or pastures. The hay consisted mainly of alfalfa with some clovers and grasses. Savannah sparrows were found in hay only when it was less than 12 inches high. The pastures were usually old hay fields containing alfalfa, clover, grasses, and some weedy plants.
The vegetation in most pastures was about V to 6 inches in height, but there were patches up to 30 inches high in some pastures.
Savannah sparrows were also found in corn fields, a mowed grass picnic area, a grassy meadow, and a weedy field. Except for one specimen in a mature corn field they were noted only in young corn 6 to 8 inches high. The grassy meadow was several acres in extent and was surrounded by a weedy upland. The birds were present in the meadow and in the edge of the weeds. One bird was taken from a weedy field full of knee-high weeds,
k 5 grasses, and brambles, but it is likely that the bird had only moved out of an adjoining hay field cemporarily.
Grasshopper sparrows were also found mostly in hay fields and pastures, often in parts where the vegetation was a little higher. They were found in the mowed grass picnic area, the grassy meadow, and the weedy field where savannah sparrows were found. They were also found in other weedy fields. Only one was seen in a young corn field and it was not collected.
Savannah sparrows were usually found only where the vegeta tion was relatively short or sparse. The areas where grasshopper sparrows could be collected overlapped those of the savannah sparrows but also included vegetation up to 3 feet high.
Bird Collections
The stomachs or stomach contents of 82 savannah and 60 grasshopper sparrows were obtained from the United States Fish and Wildlife Service. The savannah sparrows were collected by several workers between 1877 and 1938 in Illinois, Kentucky,
Michigan, Pennsylvania, West Virginia, and Ontario, Canada. The grasshopper sparrows were collected by several workers between l8?6 and 1908 is Illinois, Michigan, and Pennsylvania.
The stomach contents of these birds were measured volumet- rically in the dry state according to the method of Martin et al.
(19*1-6)• Weighing was tentatively considered as a means of mea surement, but it would have taken more time, and Jensen and
Korschgen (19^7), working with the bobwhite quail, stated that weight and volume methods gave essentially the same results. 6
Three volumetric measurements «ere recorded: (1) total volume
Including gravel, (2) volume of animal materials, (3) volume of plant materials. The number of stones present was recorded if they were not crushed into many fragments. All of the animal and plant materials were then identified as far as possible and counted. It was possible to identify plant materials, which are fairly resistant to rough treatment, to genus in most cases and species in some. Identification of plant materials was made on the basis of a reference collection and drawings (Testing Agr. and Veg. Seeds, 1952). Botanical nomenclature was based on
Gray’s Manual of Botany, Eighth Edition, by Fernald, 1950.
Animal materials were more difficult to identify because they were broken up so badly. Frequently the only indication that a beetle had been eaten was the presence of part of one elytron. For this reason many items were identified only to order, though many were identified to family and some to genus or species. Identification of animal materials was. also made on the basis of a reference collection and drawings. Zoological nomenclature was based on An Introduction to the Study of Insects by Borror and DeLong, 1954.
The numbers and sizes of animal materials were recorded.
The whole animals were placed in five size classes: up to 1 mm.;
1-3 mm.; 3-6 mm.; 6-10 mm.; over 10 mm. Some workers in the past have used other methods, notably percentage by bulk, to gain somewhat different information (Beal, 1897; Kalmbach, 1934; McAtee, 1912; Martin, 19^9), but numbers and sizes can easily be compared between animals eaten and available.
The data from these birds were combined with the data from
the birds collected in 1959 through 1961 to determine the pat
terns of seasonal variations in the two species. Collections of
the savannah sparrow were from April through November and those of the grasshopper sparrow were from March through August (with only one specimen in March and two in April).
During the summers of 1959, I960, and 1961 I collected 82 savannah and 31 grasshopper sparrows (Table 1). The birds were
Table 1. Number of Sparrows Utilized in this Study
Savannah Qrasshopper Sparrow Sparrow
Collected in 1959 25 l*f " " i960 13 3 " " 1961 Total Collected 82 31
From Fish and Wildlife Service 82 60
TOTAL 16^ 91
When discussing any one phase of the problem only those specimens which have a bearing on the matter are utilized for that particular discussion *
collected with various guns using .22 caliber bird shot for close range and shotgun shells with number 8 or 9 shot for longer range. At the time they were collected the following data were tafcen for eaoh: (1) species, (2) date, (3 ) time, (4) locality, 8
(5) habitat, (6) activities of the bird, and (7) weather data, including temperature, aloud cover, wind direction and velocity.
Within a few minutes after a bird was shot it was injected with formalin to stop digestive action. Koersveld (1951)» work ing with Corvidae, demonstrated that digestive action continues for at least 20 to minutes after death unless stopped in some manner. The first two summers 0.3 cc. of formalin was injected into the gizzard through a plastic tube inserted in the mouth.
Tests the third summer showed that 1 cc. of formalin injected into the body cavity also stopped digestion. The latter method was then utilized because it was easier and quicker. After in jection the birds were tagged.
In the laboratory the birds were frozen until they could be examined. When they were later thawed the following additional data were recorded: (8) weight, (9) sex, (10) age, (11) length of caeca, (12) presence of fat, (13) presence of intestinal para sites or other abnormalities, (Ik) materials present in the stom ach. A few birds were weighed before and after freezing as a check on the method$ the differences were slight and inconsistent.
The otomach content'd were dried, measured, and examined in the same manner as those from the United States Fish and Wildlife
Service.
The data were examined to see whether there was any correla tion between food habits and time, weather, weight, sex, age, or oaecal length, but no significant correlations at the 95 per cent level were found. In 1961 two fledgling savannah sparrows were caught alive.
Each was fed several different items of animal food over a 5 minute period. One was killed and injected with formalin 5 minutes after feeding and the other 15 minutes after feeding.
This gave an excellent check on the rapidity of digestive action on different animal foods.
Insect Collections
On the same day that a bird was collected (or at least within a few days of any bird collections) the invertebrate popu lation in the same field was sampled by sweeping. At first, scrapings from 6n or 9M mqutres of sod were also taken, but the yields were so low for the time required to take them that this method was given up in favor of making a larger number of sweep samples. Two to four samples were taken, each consisting of 20,
25. or 50 sweeps with a sweep net 15 inches in diameter. The third summer all fields were sampled with four 50-sweep samples.
This method has various drawbacks (Carpenter, 193&; DeLong, 1932
Gray and Treloar, 1933; Phillips, 1931)* but I felt that more information could be gained in a shorter amount of time by the use of sweep samples.
Two other mt'.nods of sampling were tried to determine how accurately sweeping indicated the presence of animals. One of these, the total-sample method of Wolcott (1937), consisted of inverting a 12-inch diameter garbage can over a spot of ground, pushing the sharpened edges through the sod, and fumigating the inside through a hole in the bottom. The sod was then dug up 10
and inverted over a cloth; Materials loosened by shaking and
scratching fell on the cloth. This did not work in sandy or dry
soil and was too time-consuming to sample the fields adequately.
These samples were small but they generally showed about the
same proportions of the various orders as sweep samples, with
one exception. Ground-dwelling animals such as Isopoda, Diplo-
poda, and Mollusca were picked up in some of the total-samples
but not in the sweep samples.
The second comparative method was to get a birds-eye view
by crawling on hands and knees through the vegetation looking
for animal life. An attempt was made to record all of the animal life seen in one-half hour. This was then compared with the
sweep samples from the same field, and the agreement between the
two was very close (Table 2).
The sweep samples were handled by killing the animals, put
ting them in a labeled paper bag along with any frass in the net,
and later identifying and counting them in the laboratory. The animals were classified on the basis of body length in the same manner as those from the stomachs. During the first summer ani mals were identified to species when possible. After it was realised that the animal materials in the stomachs could rarely be identified farther than family, the identification of field collections was taken only to family.
In making comparisons of animals found by sweeping with ani mals found in birds, order totals were used because of the number of animals found in birds which were identified only to order. 11
Table 2. Comparison of Sweep Samples with Observations in a Hay Field
Total of One-half Hour Order 200 Sweeps Observation
ORTHOPTERA 23 12 HEMIPTERA 187 25 HOMOPTERA 39 25 Cercopidae 801 55 COLEOPTERA ±7 9 Curculionidae 3 1 DIPTERA 22 k HTMENOPTERA 23 2 LARVAE 5 0 ARANSIDA k 1
Correlation Coefficient - .95^ Probability of a Higher Value - .01
Observations
Some observations on the behavior of the feeding birds were made in corn fields, some in more or less bare areas, and some in freshly moved hay fields and pastures. These were limited be cause the birds were frequently hidden from sight by the vegeta tion. Binoculars were used in making the observations, sinoe the birds could not usually be approached very closely. Some of the items picked up could be identified but most were too small. No observations were made on the feeding of nestlings, but two adult savannah sparrows shot during the nesting season had several items in their mouths which were probably intended for young birds. RESULTS
General Observations
Weight and Caaoal Length. Data on the weights of 76 savan nah sparrows and 29 grasshopper sparrows are shown in Table 3; naans ware not calculated for the immature birds because of the
variations in their weight due to age. There was no significant
difference in the weights of the two sexes in either species.
Caecal lengths of nost birds were measured and those of females averaged slightly longer than those of males; the difference was not significant.
Table 3* Bird Weights (in grams)
Birds Range Mean
Savannah Sparrow 30 adult males 16.1 - 20.6 18.6 16 adult females 16.1 - 20.4 18.9 10 immature birds 13.6 - 17.3
Grasshopper Sparrow 21 adult males 15*9 - 19.8 17.6 5 adult females 15*9 - 19.4 17.6 3 immature birds 14.5 - 15.9
Parasites and Abnormalities. No parasites were found in savannah sparrows, but one grasshopper sparrow had tapeworms; they were not identified. One of 19 female savannah sparrows had both ovaries present, and 1 of 54 male savannah sparrows had only the left testis present. Two of 23 male grasshopper spar rows had the right testis only. These were the only internal
12 13 peculiarities noticed. Some savannah sparrows had a much greater amount of yellow coloring on the head than others in the same field; this was not correlated with sex.
Digestive Processes. Attempts were made in 1959 and i960 to ascertain digestive rapidity in sparrow stomachs by correlating field observations with laboratory findings. In a few instances birds could be observed well enough to determine how many items of food they ingested within a given period of time. These birds were then shot and injected. The number of whole or nearly whole items in the stomach was noted and compared with the field notes.
The average number of whole animals found in the birds examined was 2.0, but the number in individual birds varied considerably. Two savannah sparrows contained 16 and 13 whole animals, and two grasshopper sparrows contained 18 and 15 ; the animals in each of these birds were Eomoptera. Most of the birds observed ate one to four items in a period of 2 minutes.
Two immature savannah sparrows were captured alive in 1961.
One bird was fed one Phalaenidae larva and three Cicadellidae and was killed and injected 15 minutes later. There were two
Cicadellidae heads in the stomach when it was opened; the head of the larva was gone but one mandible was left, and the internal parts of the larva were digested. The second bird was fed over a 5 minute period the following items in order: one Coleoptera, one Coleoptera larva, one Hemiptera, one Curculionidae, one
Hemiptera, one Phalangida. Five minutes later the bird was killed and Injected. The heads of the two Hemiptera, one with 14
the antennae attached, were present when the stomach was opened.
Fart of the head and one elytron of the adult Coleoptera were
present; the Curculionidae was whole. The Coleoptera larva and
the Phalangida were both gone. Digestion apparently takes less
than 5 minutes for medium- to soft-bodied forms but can take much longer for hard-bodied forms.
Feeding of Young. Two savannah sparrows were shot when they had their mouths full of animals. It was presumed, because of
their actions, that each was on its way to feed young birds. One bird had one Phalaenidae larva, one adult Cicadellidae, and ten
immature Cicadellidae in its beak* The other bird had nine im mature Cicadellidae in its beak. Both birds were collected in hay fields in Calhoun County, Michigan, the first on June 21,
1961, the second on July 13» 1961.
Foraging Behavior
The foraging behavior of savannah and grasshopper sparrows was quite similar but their feeding areas were different. Nearly all feeding was done on the ground, but it was done without scratching or otherwise disturbing the ground litter. The spar rows tended to move in a particular direction while feeding rather than hopping back and forth at random, but the directional movement was often in a zigzag pattern. The birds covered from
10 to 20 feet of ground per minute, their speed apparently gov erned by the number of food items present. More available items meant more pecking movements per period of time and less distance covered. Both species fed sporadically all day. 15
One savannah sparrow was observed at oloss range for 20 to
25 Minutes and it averaged about one pecking movement per minute during that time. Other birds of both species seemed to average about one to two pecks per minute, though this was quite vari able. The one savannah sparrow was observed at close range but only once could it be positively ascertained that the bird ate anything. It was suspected of eating two or three undiscernible items, and a later analysis of its stomach contents seemed to verify the suspicion. This means the bird averaged only about one item ingested every 4 minutes. Most of the birds observed appeared to ingest more items per unit of time than this bird.
Savannah sparrows nested and fed where the vegetation was less than 12 inches high and were most numerous where it was 8 inches or less in height. Grasshopper sparrows were also found in low vegetation but many were also found in vegetation over 12
Inches high. Savannah sparrows on farms tended to move to the newly mown hay fields to feed. General observations seemed to indicate that the feeding area of this species was large and without definite boundaries, and grew larger late in the simmer.
Grasshopper sparrows, on the other hand, were more confined in their wanderings, though no conflicts between males were O b ' - served. Late in the summer the birds appeared to wander quite freely from one field to the next, but grasshopper sparrows still did not wander as much as savannah sparrows. There were sexual differences in the foraging behavior of both species during the mating and nesting season. The only 16 birds ssen on perches wore singing males; this indicates that the
females stayed on the ground more than did the males. Whether
the females were feeding all of the time is not known. The males sang for 30 to *t0 minutes of eaoh hour during most of the morning and evening hours. Males in the early summer sang for 10 to 30 minutes at a time, fed for up to 10 minutes, and returned to singing again. The singing was done from a perch. As the summer progressed, less time was spent singing and more in eating. In midsummer the two species sang from the ground while feeding.
They would mount a dirt olod or other raised object, sing once or twice, and continue searching for food. The songs would be uttered from 30 seconds to several minutes apart. At the end of the summer there were no longer any noticeable sexual differ ences in feeding behavior.
Materials Eaten
Total Food Consumption. Table pages 17-19, lists all of the food materials found in the stomachs of 162 savannah spar rows. Table 5, pages 20-21, lists all of the food materials found in the stomachs of 91 grasshopper sparrows. Each table gives the number of birds that ate each type of material and the total amount eaten. The average number of animal items per bird was calculated on the basis of the birds which had eaten those items; this calculation was not made if the item was found in less than five birds. The data for plant materials are listed by genera, and the average number per bird was calculated for those genera which were eaten in large numbers by several birds. 17
Table k. Food Materials Found In 162 Savannah Sparrows*
No. of Birds No. of Items Found in which Item Avg. No. Food Material was Found Total per Bird
ORTHOPTERA Acridldae 13 22 Tettigoniidae 9 12 Unidentified b TOTAL 25 38 1.52 HEMIPTERA Reduvildae 1 1 NabIdas lb 17 Miridae 2 b Fhymatidae 1 1 Corimalaenidae 1 3 Unidentified 19 _ _ _ 3 1 ______“ t o t a l 31 57 1.85 HOMOPTERA Cicadellidae 38 13^ Cieadula sexnotata Ajrallia so. tapoasoa sp. Ceroopidae 52 201 Fulgoridae 2 13 Aphididae 2 7 t o t Il “ 355 5^30 COLEOPTERA (Adult) Carabidae 7 lb Staphylinldae 1 1 Cantharidae 6 13 Cantharis sp. Podabrus sp. Scarabasidae 3 7 Chrysomelidae 13 52 Systena blanda Curculionidae 68 1*2U Unidentified _____51 180 TOTAL 100“ “ 691 “ 6T 9T
* No data ars given for genera of animals. The difficulty of identification precludes the completeness of such data.
(Table continued) 18
Table 4. (Contd. )
No* of Birde No* of Iteaa Found in which Item Avg. No. Food Material w&a Found Total per Bird
DIPTERA (Adult) Bibionldae 1 1 Stratioayidae 6 18 Muaooidea 3 3 Unidentified 5_ 8 TOTAL 13 30 2.31 _ HYMENOPTERA (Adult) Foraicidae 3 6 Apoidea l 1 Unidentified 23- - - TOTAL 37 62 1.67 LARVAE Lepidoptera 38 64 Paeudaletia unipuncta Nephelodea earnadonla Plathypena acabra Pieria rapae Coleoptera 6 34 Hymenoptera 2 2 Unidentified 8 14 TOTAL ,?9 114 2.33 _ NEUROPTERA (Adult) Heaerobiidae 1 1 ODONATA, Zygoptera 2 2 INSECT EGGS 6 20 3*33 ARANEIDA 12 16 1.33 PBALANOIDA 2 2 CHILOPODA 1 2 MOLLUSCA 5 8 1.6o UNIDENTIFIED ANIMALS 2 2
TOTAL ANIMAL MATERIALS 148 1400 9.46
(Table continued) 19
Table k. (Contd.)
No. of Birds No. of Iteas Found in which Item Avg. No. Food Material was Found Total per Bird
GRAMINEAE Broaue so. 1 1 Festaca an* 1 3 Poa sp. 5 26 Eraicrostis sp. 1 18 Arena satire 1 1 Alopecurus sp. 6 7 2 Phleus pretense 3 23 Digitaria sp. 22 658 29.50 Pan!c u m spp. 32 if73 1^.80 Eohinochloa crusfcalli 10 143 1.43 Sstarla lutesoens. 6. riridis, S. italica ^6 385 8.37 Unidentified ______J>______TOTAL B7 - -o?8“i8¥i - 2 1 . l£ NON-GRASSES Cjperaceae k 17 Rumex sp. 1 1 Polygonum spp. if 6 Chenopodiua sp. 1 1 Anaranthus sp. 3 19 Portulaca oleracea 2 32 Stellaria aedia 2 2 Silene sp. 1 2 Brassioa sp. 12 122 10.15 TrifolluM sp. 2 2 Oxalis sp. 26 97 3-73 Eujghorbia sp. 3 32 Cusouta pentagons 1 9 Verbena sp. k 18 Physalis sp. 1 1 Verbasona sp. 1 1 Compositae k 72 Ambrosia artemislifolia 6 6 Anthemis cotula 1 3 Cirsiua spp. 5 18 Unidentified 5 TOTAL 59 7 . 3 0
TOTAL PLANT MATERIALS 100 2307 23.07 20
Table 5 . Food Materials Found In 91 Grasshopper Sparrows*
No. of Birds No. of H teas Found in which Item Avg. No. Food Material was F iund Total per Bird
0RTH0PTERA Acrididae 4o 83 Tettigonlidae 15 25 Unidentified 12 25 _ TOTAL 50 133 2.6 b HEMIPTERA Nabidae 22 47 Lygaeldae 2 3 Phynatidae 3 3 Unidentified 15 36 TOTAL 32 *9 2.78 H0M0PTERA Cioadellidae 15 48 Cercopidae 16 85 Unidentified 5 7 TOTAL __ 30 140 4.67 COLEOPTERA (Adult) Carabidae 4 4 Cantharidae 1 2 Elateridae 1 1 Scarabaeidae 3 4 Chrysomelidae 8 19 Systena blanda* Curculionldae 27 95 Unidentified ______15______19 TOTAL 5i 184 3.12 DIPTERA (Adult) Syrphidae 1 1 HYMENOPTERA (Adult) Fornicidae 5 5 Apoidea 1 1 Unidentified _ _ _ __ 8 ___13______“t o t a l ~ 13 19 1.46
* No data are given for genera of animals. The difficulty of identification precludes the completeness of such data.
(Table continued) 21
Table 5. (Contd.)
No. of Birda No. of I tenia Found in which Item Ayg. No. Food Material vaa Found Total par Bird
LARVAE Lepidoptera 35 63 Paeudaletia unipunota Nephelodea ennadonia Papaipeaa nebria Unidentified 5 7 TOTAL 38 70 1.85 LEPIDOPTERA (Adult) 1 1 ODONATA, Zygoptera 1 1 INSECT EGGS 2 4 ARANEIDA 18 2k 1-33 MOLLUSCA 4 4 UNIDENTIFIED ANIMALS 1 1
TOTAL ANIMAL MATERIALS 90 670 7.44
GRAMINXAE Broaua ap. 1 17 Poa ap. 4 31 Dactylla gloaeratue 1 2 Avana aatira 1 5 Aaroatla ap. 1 1 Phleua pratenae 9 229 25.44 Dijtitaria ap. 1 4 Panioua ap. 7 49 Echinoahloa cruagalli 1 21 Sataria lateaoana. S. viridia 42 686 16.33 Unidentified _ _ -7 _ _ 127 TOTAL Zz 1172 18.90 NON-GRASSES Ruaex ap. 1 1 Polyiconua sp. 2 18 Medioajto ap. 1 3 Oxalia ap. 19 94 4.95 Varbana ap. 1 1 Aabreaia arteaiaiifolia 10 30 Ciraiua ag. 1 5 TOTAL 31 .132 4.90
TOTAL PLANT MATERIALS 68 1324 19.50 22
The most important animal materials in the diet of savannah sparrows were Coleoptera, Homoptera, and larvae, and in the diet of grasshopper sparrows were Orthoptera, Coleoptera, larvae, and
Hemiptera. The most common animals found by sweeping, in order of their abundance, were Homoptera, Coleoptera, Hemiptera, Or thoptera, and Diptera. Larvae were found in sweep samples less often than any other major group. The ranking is based on a compilation of sweep data from three summers.
Table 6 is a comparison of the orders of animals, groups of plants, and numbers of stones found in the two sparrows. The two families Cercopidae and Curculionidae and the genus Setaria are listed separately. The Cercopidae are separated because they occurred so abundantly in the field, the other two because they were eaten in large numbers.
The average number of stones per savannah sparrow was 9.95 in April, reached a low of 1.04 in June, and was 19.7 in October.
Savannah sparrows ingested more stones at all times than did grasshopper sparrows.
Figure 1, page 29, shows the proportions of plant and animal materials eaten by savannah sparrows from April through November, and Figure 2 shows these proportions for grasshopper sparrows from May through August. The savannah sparrow feeds almost en tirely on seeds in the winter (Quay, 1958), and almost entirely on animals in the summer. Grasshopper sparrows lag behind savan nah sparrows about one month in their spring transition from a vegetable to an animal diet. 23
Table 6. Materials Eaten by Savannah and Grasshopper Sparrows
Savannah S parrow Grasshopper Sparrow Per cent of Per cent of Birds which Avg. No. Birds which Avg. No. Orders Ate Item per Bird Ate Item per Bird ORTHOPTERA 15-4 1.52 55-0 2.66 HEMIPTERA 19.1 1.84 35.2 2.78 HOMOPTERA* 24.1 3.94 19.8 3.06 Cercopidae 32.1 3.86 17.6 5.31 COLEOPTERA (Adult)* 41.3 3.98 48.4 2.02 Curculionidae 42.0 6.24 29.7 3.52 DIPTERA (Adult) 8.0 2.31 1.1 1.00 HTMENOPTERA (Adult) 22.8 1 .6? 1^.3 1.46 LARVAE 30.3 2.33 41.8 1.84 ARANEIDA 7.4 1.33 19-8 1.33
Setaria spp. 28.4 8.37 46.2 16.33 OTHER GRASSES 39.5 22.75 30.8 17.35 NON-GRASSES 36.4 7.90 34.1 4.90
STONES 70.3 9.26 50.6 5.22
* Exclusive of family listed e
The data from which Figures 1 and 2 were drawn agree fairly closely with the figures given by Martin et al. (1951)* Animals made up only about 33 per cent of the number of items eaten but because of their size they composed about 73 per cent of the volume.
Sice of Materials Eaten. All animals in a bird or in a sweep sample were put in size categories. Eighty-six per cent of the animals eaten were from 3 to 10 mm. long (1198 of 1393 items). The ingested animals Imnger than 10 mm. (98 of 1393 items) were Orthoptera, larvae, and a few Coleoptera, and those 2k
Per cent of Total
Apr. May June July Aug. Sep. Oct* Hot. Figure 1. Per cent of animal food In the diet of 162 savannah sparrows; remainder is plant food. (Based on volume.)
Per cent
Apr. May June July Aug. Sep. Oct. Figure 2. Per cent of animal food in the diet of 90 grasshop per sparrows; remainder is plant food. (Based on volume.) 25
less than 3 mm. long (97 of 1395 items) were nearly all Coleop
tera, mostly Curculionidae, and vere at least 2 mm. long. A
great many, frequently over one-half, of the animals in sweep
samples were less than 3 mm. long; these were mainly Homoptera,
Dlptera, Hymenoptera, and Coleoptera.
No animals in the sweep sample data except Coleoptera were used in comparisons unless they were at least 3 mm. in length;
Coleoptera were counted from 1 mm. up. This appeared to be a more valid way of counting available animals than to count all of the animals present.
Intraspecific Variation. There were 16 occasions during
the three summers of collecting when two or more savannah spar rows were collected from a given field on the same day. The data were pooled for each of the 16 stations, and in each case two
figures were derived: the average number of animals per bird for each order, and the average number of animals per sweep for each order. The average number of animals per bird was calculated on
the basis of all birds colleoted at a given station on a given date. A statistical analysis was then made for each order to determine the regression of animals per bird on animals per sweep. The standard error and Student's t were also calculated.
A second analysis was made using only the 12 stations where three or more savannah sparrows had been taken. The difference in re sults in the two analyses was negligible in most cases, and in no case did it change the significance of any results. 26
Table ? shows the numbers of Orthoptera per bird and per sweep for each of the 16 stations. None of the data for other orders are tabulated because only the Orthoptera showed a signif icant regression of animals per bird on animals per sweep.
Table 7. Comparison of Orthoptera per Bird with Orthoptera per Sweep in Savannah Sparrows
Type of No. Animals Animals Date Field Birds per Bird per Sweep 5-29-59 Pasture 10 - .10
6-21-61 Corn 3 - .01
6-21-61 Hay 2 --
6-21-61 Hay 2 -- 6-26-61 Corn 2 • 50 .01 6-26-61 Pasture 4 - .04 7- 4-59 Hay 5 .20 .18 7- 4-59 Corn 4 - .04 7- 4-59 Pasture 6 .84 .86 7-15-61 Hay 11 .54 .12 7-16-60 Hay 7 .43 .35 7-16-60 Pasture 3 .67 .08
7-29-61 Pasture 2 • 50 • 56 8- 1-61 Hay 4 1.25 .54 8-11-61 Hay 6 .84 1.55
8-50-61 Hay 4 - .28
Regression Coefficient - .82 Standard Error - .22 Student's t with 14 degrees of freedom - 3.73 Probability of larger value of t - .01
All of the orders except Diptera, Hymenoptera, and Araneida showed an iaorease in numbers in the fields during the summer. 27
Those three orders maintained relatively constant numbers during
the summer. Savannah sparrows ate grasshoppers and Homoptera in
increasing numbers during the summer but seemed to eat other ani
mals in a sporadic manner. The relative numbers of each order
that were eaten during the summer can be seen in Figures 3 to 9,
pages 3& in b2. The birds had their peak intake of several
orders during June or July. The animals preyed upon were usually
fairly abundant at that time but some orders reached their maxi
mum adundance in August.
Comparisons were made within fields between the numbers of
each order eaten by savannah sparrows and the numbers of each
order present. In no case was there a significant regression of
numbers eaten on numbers present; the proportions of animals
eaten did not depend upon the proportions in which they were
present. Some animals that were relatively scarce were eaten
in large numbers (particularly Curculionidae), while others that
were numerous were eaten in small numbers.
Both sexes of the savannah sparrow were collected from three
fields in sufficient numbers, 17 males and 10 females, to make
comparisons. No substantial differences were found in types or
numbers of animal foods eaten by the two sexes. Females seemed
to eat fewer seeds in the late spring than did the males, but
there were not enough data to support a conclusive judgment.
The individual variation between specimens, all of which
were taken from one field on one day, was usually not great, but was always noticeable. The numbers and kinds of materials eaten 28
by 11 specimens collected from a hay field on July 13, 1961, are
tabulated In Table 8. One reason for the apparent individual
variation is that even though all of the birds might eat the same
things, they would not eat the same things at the same time* A
second factor which contributes to the variation is the rapidity
with which some items leave the stomach of the bird.
Table 8. Numbers of Food Items of 11 Savannah Sparrows Taken from a Hay Field on July 13, 1961, Calhoun Co., Michigan
Food Material______dddddddQQQQ Acrididae Hemiptera 1---111---1 Nabidae -----12--12 Cicadellidae 6118 721110 213 Cercopidae 24356632235 Coleoptera ------2- Chryaomelidae Curculionidae — — — — — — A|-*6 — Lepidoptera adult ------1 Lepidoptera larva ------1-1.2 Araneida ---1---2--- Gramineae __-2----l-- Stellaria
Some birds ate one item in large numbers to the exclusion
of other types of food, but this was unusual* Several birds ate much larger numbers of one item than of anything else; e.g., one
bird colleoted on June 2 6 , 1961, contained, among other things,
64 small Chrysomelidae of two species. This was most common with birds that ate Curculionidae or various seeds, and occasionally 29 with birds that ate Cercopidae or Cicadellidae. The number of
other iteme eaten varied when one item was eaten in large numbers.
There were only eight occasions during the three summers of
collecting when two or more grasshopper sparrows were collected
from a given field on the sane day. The data from each of the
eight stations were handled in the same way as those from savan nah sparrows (see page 25)* and the Orthoptera data are presented
in Table 9* The data for other orders are not tabulated because
the grasshopper sparrow, as did the savannah sparrow, showed a
significant regression of animals per bird on animals per sweep
only with the Orthoptera. The relative numbers of each order
that were eaten during the summer can be seen in Figures 3 to 9* pages 36 to 42.
Table 9* Comparison of Orthoptera per Bird with Orthoptera per Sweep in Qrasahopper Sparrows
Type of No. Animals Animals Date Field Birds per Bird per Sweep
5-25-61 Pasture 2 - .02 5-29-59 Pasture 3 - .10
6-17-61 Weeds 2 - .10 6-27-61 Weeds 2 - .55 7- 4-59 Pasture 4 1.50 .86 7-29-61 Pasture 5 .80 .56 7-31-59 Meadow 4 1.25 .90 8- l-6l Hay 2 1.50 .54
Regression Coefficient - 1.60 Standard Error - .36 Student's t with 6 degrees of freedom -• 4.05 Probability of larger value of t - .01 Comparisons were made within fields between the numbers of
each order eaten by grasshopper sparrows and the numbers of each
order present. In only two cases was there a significant regres
sion of numbers eaten on numbers present: July 1959, in a
pasture and July 31, 1959, in a grassy meadow. The data from
these two fields are presented in Table 10. Data from other
fields are not presented, since there were no significant regres
sions.
There were not enough female grasshopper sparrows collected
in any one place to make meaningful comparisons with males, but
nothing unusual was noted concerning the diets of females as
compared with males in the specimens which were collected.
The individual variation between specimens taken from a
given field on the same day was about the same as in savannah
sparrows, with one exception; the diet of immature grasshopper sparrows seemed to be more limited in variety than the diet of
immature savannah sparrows. The numbers and kinds of materials
eaten by four adult specimens collected from a pasture on July
1959, are tabulated in Table 11.
The reasons for individual variation are the same as those given for individual variation in the savannah sparrow. With their breadth of diet the birds did not all eat the same things at the same time; differential rates of digestive rapidity help to determine what is present when the stomachs are examined.
Some of the grasshopper sparrows ate much larger quantities of 31 one item than of anything else. The Items eaten In larger num bers were Cercopidae, Curculionidae, and some seeds.
Table 10. Comparison of Animals per Bird with Animals per Sweep in Qrasshopper Sparrows from Two Fields
Date 7-4-59 7-31-59 _ Field Past;ure Meadow Animals Animals Animals Animals Order per Bird per Sweep per Bird per Sweep ORTHOPTERA 1.50 .86 1.25 .90 HEMIPTERA 1.25 .04 - .34 HOMOPTERA *50 .18 .25 .18 Cercopidae 9*25 .90 5.25 3.8* COLEOPTERA .50 .30 .50 .42 Curculionidae *53 .02 .50 .04
DIPTERA - . Ob - .06
HYMENOFTERA .25 . 06 - • 34 LARVAE .50 .1? 1.00 .04 ARANEIDA - - .25 . 68
Regression data for July 4, 1959: Regression Coefficient - 5.88 Standard Error - 1.99 Student’s t with 8 degrees of freedom - 3*035 Probability of larger value of t - .02
Regression data for July 51, 1959* Regression Coefficient - 1.215 Standard Error - .512 Student’s t with 8 degrees of freedom - 8.26 Probability of larger value of t - .01 52
Table 11. Numbers of Food Itome of Four Adult Grasshopper Sparrows Taken from a Pasture on July 9-, 1961, Marion Co., Ohio
Food Material cf 9
Acridldae 2 1 1 2 Hemiptera - - 1 - Nabidae 1 - 2 - Phymatidae - - 1 - Cicadellidae - 1 - 1 Cercopidae 10 2 10 15 Coleoptera - - - 2 Curculionidae - 1 1 - Formicidae - - - 1 Lepidoptera larva 1 - - 1 Setaria viridis - 1 - - Oxalis sp. 1 - 1 17 Cirsium sp. - - - 5
Interspecific Comparisons. Savannah and grasshopper spar
rows were similar in their foraging habits, and when they were both foraging in the same field the materials they ate were simi
lar. Several fielda were found where both species occurred, but usually only a few individuals of one species occurred with many of the other. In several cases only one specimen was obtained of one of the two species; in only three fields were enough specimens of both species obtained for comparisons.
Ten savannah and three grasshopper sparrows were collected in a pasture on May 29, 1959* and six more savannah and four more grasshopper sparrows were collected from the same pasture on July
9-, 1959* Four savannah and two grasshopper sparrows were 33
collected from a hey field on August 1, 1961. The data obtained
from the three collections are tabulated in Table 12 as animals
per bird. A statistical analysis indicated that the diets of the
two species were significantly correlated in the three cases.
Table 12. Comparison of Animals Eaten by Savannah and Grass- hopper Sparrows in Three Fields in Marion Co. , Ohio
5-29-39 7-4-59 8-1-61 Pasture Pasture Hay Field Order 10 _Sav.b Gras. 6 Sav. 4 Gras. 4 Sav. 2 Gras.
ORTHOPTERA - .84 1.50 1.25 1.50 HEMIPTERA .30 - 1.17 1.25 - - HOMOPTERA 1.30 - .50 .50 4.25 1.00 Cercopidae -- 6.84 9.25 2.25 1.50
COLEOPTERA 3.00 - .50 .50 2.00 - Curculionidae 4.70 5.00 - .50 2.50 .50 DIPTERA 1.70 - - - - - HYMENOPTERA .50 - • 50 .25 .50 - LARVAE 1.30 .70 .50 • 50 2.25 1.00 ARANEIDA .10 • 30 - - - -
Correlation .916 Coefficient _ .997 • 723 Probability of .01 .01 a Higher Value .02
The diets of savannah and grasshopper sparrows were not as biologically similar as the correlation coefficients in Table 12 indicate. The data from May 29 shows that the savannah sparrows consumed eight different items, while the grasshopper sparrows consumed only three, but the correlation coefficient is signifi cant at the 99 per cent level. Table 6, page 23, shows that 3^ over the summer the two species consumed the same types of mate rials but in different amounts.
There was an impression when sweeping and when first looking at the sweep data that Orthoptera, Hemiptera, and Araneida were more numerous in higher vegetation and that Cercopidae were more numerous in lower vegetation. This agrees with comparative num bers eaten by grasshopper and savannah sparrows in their respec tive habitats. Statistical treatment, however, did not bear out the impression, and Curculionidae, which seemed most abundant in higher vegetation, were eaten in greatest numbers by savannah sparrows.
There was a difference between the two species in the pro portions of the diet composed of animal versus plant materials.
A greater prorortion of the diet of savannah sparrows in early summer consisted of animal materials than did the diet of grass hopper sparrows. This is shown in Figures 1 and 2, page 2^.
Figures 3 to 9 show graphically the relative numbers of each order eaten by the two species each month. The time covered was April through October for the savannah sparrow and May through August for the grasshopper sparrow. The number of ani mals eaten per bird is based on all of the birds collected that month and includes the recently collected specimens and those from the Fish and Wildlife Service.
Figures 3 to 9 show when the peak intake of each order oc curred in each species and the relative abundance of each order in the field. The relative abundance is derived from a compilation of sweep data from several fields sampled during the three year collecting period. The data for relative field abun dance is only an approximation and the scale for each figure is not the same.
When the peak intakes of the orders were compared with their peak abundance it was found that the peaks coincided for Orthop tera and Cercopidae in the savannah sparrow and for Orthoptera,
Cercopidae, larvae, and Hymenoptera in the grasshopper sparrow.
The peaks of abundance of Homoptera and larvae in the savannah sparrow and in the fields overlapped, though they did not coin cide. 5 Savannah — — Grasshopper - - - Relative Abundance in Field — o—
3
2
1
11 3522 16 7 Numbers of Savannah Sparrows 25 15 39 13 Numbers of Grasshopper Sparrows
Figure 3» Number of Orthoptera par bird eaten by savannah and grasshopper sparrows. 5 Savannah ----- Grasshopper - - - Relative Abundance in Field o
2
1
Apr. Mar June July Aug. Sep. Oct. 11 35 22 kj 16 7 23 Numbers of Savannah Sparrows 23 15 39 13 Numbers of Grasshopper Sparrows
Figure J+. Number of Homoptera per bird eaten by savannah and grasshopper sparrows. 38
5 SaTannah - — Grasshopper - - - Relative Abundance in Field — o— k
3
2
1
Apr. Kay June July Aug. Sap. Oct. 11 35 22 *13 16 7 23 Rushers of Savannah Sparrows 23 15 39 13 Rushers of grasshopper Sparrows______
Figure 5* Nusber of Cercopidae per bird eaten bj savannah and grasshopper sparrows. 8 SaTannah 1 Qrasahopper - - - RelatiTe Abundance in Field — o— 7
6
5
k
3
2
1
Apr. Maj June J»ly Aug. Sep. Oct. 11 35 22 **3 16 7 23 Hunbera of SaTannah Sparrow______23 15 39 13 Ifunbsra of Qraaahopper Sparrows
Figure 6. Nunber of Coleoptera per bird eaten bj eaeannnh and grasshopper sparrows. 8 Savannah ----- Grasshopper - - - Relative Abundance in Field — o— 7
6
5
4
3
2
--- 1
Apr. May June July Aug. Sep. Oct. 11 35 22 43 16 7 23 Nusbera of Savannah Sparrows______23 15 39 13 Nusbera of Grasshopper Sparrows______
Figure 7. Nuaber of Curculionidae per bird eaten by savannah and grasshopper sparrows. kl
2 SaTannah — — Grasshopper - - - Relative Abundance in Field — o—
Hemiptera1
3
2
1
Apr. May June July Aug. Sep. Oct. 11 35 22 *0 16 7 23 Numbers of Savannah Sparrows 23 15 39 13 ______Numbers of Grasshopper Sparrows
Figure 8. Number of Hsmiptera and larvae per bird eaten by savannah and grasshopper sparrows. 42
2 Savannah ----- Oraeahopper - - - Relative Abundance in Field — o—
Diptera 1
2
1
1 Araneida
o — ■
Apr. May June July Aug. Sep. Oct. 11 35 22 43 16 7 23 Numbers of Savannah Sparrowa______23 15 39 13 Nuabera of Grasshopper Sparrows______
Figure 9* Nunber of Diptera, Hymenoptera, and Araneida per bird eaten bj savannah and grass hopper sparrows. DISCUSSION
Savannah and grasshopper sparrows do not eat animals (exeept
Orthoptera) In proportion to the numbers In which the animals occur In the fields. This Is interpreted as indicating that savannah and grasshopper sparrows show preferences in the animal foods they eat. Savannah sparrows differ more than grasshopper sparrows in intake compared to numbers present; grasshopper sparrows select fewer items from the total available than do savannah sparrows. Both species show a definite size preference for animals 3 to 10 am. in length.
A comparison of numbers of animals present, as indicated by sweeping, with numbers of animals eaten shows that the numbers eaten are disproportional to the numbers present, particularly in the savannah sparrow. The period of greatest consumption of some orders of animals, however, corresponds to the period of their greatest abundance. During other times orders are eaten in relatively small numbers because they have been more or less replaced in the diet by an order which may have reached its peak of abundance.
Five groups of animals account for most of the animal mate rial eaten during the summer: Orthoptera, Hemiptera, Homoptera,
Coleoptera, and larvae (mostly Lepidoptera). The Orthoptera and
Homoptera are relatively fast-moving but during part of the sum mer they occurred in excessively large numbers. The other three groups are relatively slow. Their abundance varied during the summer but they were present at all times. Between one-third and
*3 kk one-half of the Hemiptera eaten were Nabidae, which are relative ly large and alow. One-half of the Coleoptera eaten were Curcu lionidae, which are very slow-moving, as are larvae.
The two species of sparrows showed a difference in overall preferences. The diet of the savannah sparrows included many more items than did the diet of grasshopper sparrows, and, over the whole summer, the two species did not eat things in the same proportions.
Several factors are probably involved in the relative pre ferences of savannah and grasshopper sparrows. Maximum intake of some orders occurred at or near the time of peak abundance in the fields. This indicates that the total numbers present of some orders can modify preferences. Numbers by themselves, how ever, probably do not determine the availability of animals; the speed of the animals may affect their availability to the sparrows. The birds made many pecking movements for each item of food obtained, indicating that probably many animals escaped.
One would have to determine an "escape value" for each order to be used with total numbers present to allow for the effect of speed in the determination of actual availability. The "escape value" might be an estimate of the percentage of an order eaten under certain given conditions.
The sparrows ate very few animals less than 3 ®m. in length.
They probably do not abstain from smaller animals because of poor eyesight; they feed on many seeds that are 1 to 2 mm. in length. It is possible that the effect of speed is exaggerated ^5 by the small size. Most of the animals eaten that were less than
3 mm. long were Curculionidae, which are very slow.
Protective coloration of the animals eaten may play a part in the preferences of the birds, but there was no apparent evi dence of this. None of the animals eaten eeemed any less well protectively colored than those not eaten except Aphididae. Few
Aphididae were eaten but most were below the size limit taken by the birds.
The interspecific differences could have been due to one or more of three things: (1) There may have been differences in availability of animals in the different habitats greater than those detected by sweeping, as the sweep sample usually did not indicate habitat differences of the magnitude of those found be tween species; (2) the differences could have been a matter of taste, since some animals may be more palatable to one species than to the other; or, (3) they could have been due to innate or learned behavior patterns expressed as different preferences
(e.g., different reactions of the two species to movements of the prey, or different learned habits due to training on differ ent foods in microhabitate). *
The sparrows generally spent a large part of the day feed ing, as noted by Stevenson (1933), but because of their manner of feeding they do not get as much food as might at first be surmised. They move a distance of several feet for every item of food taken, and with seeds in particular the items eaten are frequently quite small. 46
Steiniger (1937b) claimed, as did McAtee (1932), that the protectire adaptations of insects are only relative and may pro tect them from some birds but not from others. The findings of this study seem to lend support to this assertion.
Jones (1954) found that pigeons could distinguish better between forms than between colors or positions. This would be helpful in recognizing certain types of insects if sparrows are also good at distinguishing forms.
Three workers found that certain birds ate food materials in the proportions in which the foods were available: Quay
(1958), working with the savannah sparrow in winter, Stenger
(1958), working with the ovenbird, and Stoddard (1931) working with the bobwhite quail. Quay (195$) also found that savannah sparrows rarely ate any seeds larger than 3 And then only by cracking them first.
Several workers have found that many birds do express pre ferences in their diets: Judd (1897), working with the catbird,
Salt (1957), working with three species of sparrows, Bookhout
(1958), working with bobwhite quail, Hawkins (1937), working with four gallinaceous species, Ticehurst (1940), working with several species in different orders, and others. Hartley (1954) found that four species of Turdus ate about the same fruits but each species had a different preference. The same thing is true of the two species of sparrows with respect to animal foods. Bruns
(1952) observed that titmice (Parus spp.) preferred cucumber seeds that had black markings on the ends to those that were ^7 plain or striped. Various workers have found food preferences in a wids variety of other animals; Lindsay (1958) found that Dro sophila larvae have food preferences for certain yeastB.
HBglund (1955) showed that if capercaillie chicks (Tetrao uroaallus) are given a choice between colored beads when they first begin to feed they will usually try to eat green beads rather than red, yellow, or black ones. The chicks normally feed on green plant material. They have instinctive movements, accord ing to HtJglund, which are followed quickly by a directed hunt based on availability and experience. Engelmann (1951) observed that chickens had the ability to recognize food and the least at tractive plants were recognized best. Their memory was also bet ter for colored grains than for plain ones, and they could recog nize specific food objects up to more than 100 days. Bene (19^5) found that the feeding habits of black-chinned hummingbirds
(Archilochus alexandri) are modified by experience, particularly during the first two weeks they feed. These findings support the idea that part of the interspecific variation may be due to dif ferent learning experiences.
According to MacArthur (1958), several species of warblers may feed in the same tree but they feed in different parts and in different ways and thus do not overlap. Hartley (1953) found that there was an ecological separation of titmice but that it disappears in times of superabundance of food. It is not known whether there was a superabundance of food available to the sparrows, but there probably was in July and August. 48
Dove (1935) conducted an experiment in which many different foods were offered to groups of chicks at the same time and the amount of each food eaten was recorded. Subsequent weight gains and longevity were recorded, and the chicks were periodically segregated into groups according to weight gained. He found that the chicks were widely variable in their choices. He also found that a diet slightly higher than average in amount eaten and variable in content gave good growth gain and best longevity; correct preferences led to a longer life.
Preferences for animal foods in savannah and grasshopper sparrows are probably based on a combination of size, numbers, and speed of movement of the prey. Interspecific differences are probably due to some differences in availability and dif ferent preferences, either learned or innate.
Some unsolved problems present themselves. One problem is determining actual availability, what it is, and how it is af fected. This might be approached by releasing a given number of animals into a cage with a sparrow and determining the percentage eaten within a given period of time. Only one type of animal could be released at a time and preferably in a cage containing some vegetation. A second problem is how habit and experience influence food preferences. This might be approached by rearing young birds on certain selected items for a period of time and then determining what they do when presented with a wide variety of items including those on which they were reared. SUMMARY
Eighty-two savannah sparrows and 31 grasshopper sparrows were collected from various cultivated and weedy fields in Ohio and Michigan during the summers of 1959, 19&0, and 19&1. Eighty- two additional savannah sparrows and 60 additional grasshopper sparrows were obtained from the United States Fish and Wildlife
Service. The stomach contents were analyzed for taxonomic and volumetric content. The animal portion of the taxonomic content was then compared on a proportional basis to the taxonomic con tent of the fields where the birds were collected as determined by insect sweeping. Comparative measurements were made of the weights of the birds.
Many animal materials break up in the stomach in five minutes or less. Foraging behavior was the same in the two species. The habitats utilized by the two species overlapped.
The total foods eaten by each species were listed and the per centages of plant and animal foods were compared through the summer for both species. The two species ate the same types of animals but in different amounts. Both species showed a distinct preference for animals over 3 in length.
Orthoptera were eaten in proportion to the number present by both species through the summer; this was not true of other orders. In middle and late summer grasshopper sparrows seemed to eat animals in the proportions in which they occurred in the fields, but this was not true of savannah sparrows at any time.
There were no differences in animal foods taken by males and females in either species. Both species showed preferences for certain groups; savannah sparrows ate mainly Coleoptera, Homop- tera, and larvae, and grasshopper sparrows ate mainly Orthoptera,
Coleoptera, larvae, and Hemiptera. The diets of savannah and grasshopper sparrows which fed In the same fields were similar but not identical. The two species of birds show preferences based on the sise, numbers, and speed of movement of the animals present. Some suggestions are given for possible further lines of research. BIBLIOGRAPHY
Beal, F.E.L. 1897* Recent investigation* of tha food of
European birda. Auk, 14(1):8-14.
Beal, F.E.L. and W.L. MoAtee. 1912. Pood of aone well-known
birds of forest, fara and garden. Earners Bull. No. 506,
35 p.
Bene, Frank. 19^5* The role of learning in the feeding behavior
of blaek-chinned huaaingbirds. Condor, V7(l)i3-22.
Bookhout, T.A. 1958- The availability of plant seeds to bob-
white quail in southern Illinois. Ecology, 39(*0*671-681.
Borrero, J.I. 1953. Notaa prelialnares sobre habitos
allaentielos do paloaas silvestres Coluablanas. Caldasia,
6(27):75-80.
Borror, D.J. and D.M. DeLong. 195^* An Introduction to the
Study of Inseets. Rinehart and Co., New York, 1030 p.
Bradley, H.L. 19^0. A few observations on the nesting of the
Eastern Chipping Sparrow. Jaok-Plne Warbler, 18*35-46.
Bruns, H. 1952. Die Bedeutung optisoher Merkaale des Futter-
platses und des Futters fVr nahrungsuohende Meisen.
Biol. Zentralbl., 71(1/2)t69-108.
Butts, W. K. 1927. The feeding range of certain birds. Auk,
W 3 ):329-350.
Carpenter, J.R. 1936. Quantitative ooaaunity studies of land
anlaals. Jour. Aniaal Eeol., 5(2):231-245.
51 Cottaa, Clarence. 1936. Econoaic ornithology and the correla
tion of laboratory and flold methods. U.S. Dapt. Agr.
Wildlife Rea. and Mgat. Leaflet BS-30, 13 p.
Davison, V.B. 19*K). A field aethod of analysing gaae bird
fooda. Jour. Wildlife Mgat., *f(2)»105-116.
Dawson, R.W. 19^2. Inaect control by birde. Flicker, l*f(l)tl-5-
DeLong, D.M. 1932. Some probleaa encountered in the eatiaation
of insect populations by the sweeping aethod. Ann. Ent.
Soc. Aaer., 25(1):13-17.
Dove, W.F. 1933* A study of individuality in the nutritive
instincts and of the causes and effects of variations in
the selection of fooda. Aaer. Nat., 69(72*0:**69-5i*^.
Engelaann, C. 1951• BeltrSge sua Gedlohtnis des Huhns.
Seitsohr. Tierpsychol., 8(1):110-121.
Fernald, M.L. 1950. Gray*a Manual of Botany, 8th Ed.
Aaerlean Book Co., New York, 1632 p.
Festinger, Leon. 19^3* Developaent of differential appetite
in the rat. Jour. Exp. Psychol., 32(3): 226-23*f.
Gray, H.X. and A.E. Treloar. 1933* On the enuaeration of
Insect populations by the method of net collection.
Ecology, l^(^)t356-367.
Hanson, W.R. and F. Graybill. 1956. Sample slse in food-habits
analyses. Jour. Wildlife Mgat., 20(1)*64-68.
Hartley, F.H.T. 1953* An ecological study of the feeding habits
of English titmice. Jour. Aniaal Ecol., 22(2):261-288. Hartley, P.H.T. 1951*-. Wild fruits in the diet of British
thrushes. A study in the ecology of closely allied species.
Brit. Birds, k?(k)t97-107-
Hawkins, A.S. 1937* Winter feeding at Faville Grove, 1935-36.
Amer. Midi. Nat., 18(3):417-^25.
H#glund, N.H. 1955* Influence of different colours on the
capercaillie chick's choice of food. Viltrevy, 1(1):122-128.
Hyde, A.S. 1939* The life history of Henslow's sparrow.
Misc. Publ. Mue. Zool. Univ. Mich., ^1:1-72.
Jensen, G.H. and L.J. Korschgen. 19^7* Contents of crops,
gizsards, and droppings of bobwhite quail force-fed known
kinds and quantities of seeds. Jour. Wildlife Mgat.,
11(1)*37-^3.
Jones, Lyle V. 195^< Distinctiveness of color, fora, and
position cues for pigeons. Jour. Comp, and Physiol.
Psychol., *f?(3)*253-257.
Jones, Lynds. 1913* Some records of the feeding of nestlings.
Wilson Bull., 25(2):67-71.
Judd, S.D. 189?. Methods in economic ornithology, with special
reference to the catbird. Aaer. Nat., 31(190):392-397.
Judd, S.D. 1901. The relation of sparrows to agriculture.
U.S. Div. Biol. Surv. Bull. No. 15, 98 p.
Judd, S.D. 1902. Birds of a Maryland farn: a local study of
econoaic ornithology. U.S. Div. Biol. Surv. Bull. No. 17,
116 p. Kalmbach, E.R. 193^* Field observation in economic ornithology.
Wilson Bull., ^6(2):73-90.
Knowlton, Q.H. 1990* Insect food of the Nevada savannah
sparrow. Auk, 67(1)»106.
Koersveld, E. van. 1951* Difficulties in stomach analysis.
10th Internet. Ornithol. Cong. Proc., p. 592-59*f.
Leopold, A.S. 1953* Intestinal morphology of gallinaceous
birds in relation to food habits. Jour. Wildlife Mgmt.,
17(2):197-203.
Lindsay, S.L. 1958* Food preferences of Drosophila larvae.
Amer. Nat., 92(866)*279-285.
MacArthur, R.H. 1958. Pbpulation ecology of some warblers of
northeastern coniferous forests. Ecology, 39(iO *599-819.
McAtee, W.L. 1912. Methods of estimating the contents of
bird stomachs. Auk, 29(*0 *
McAtee, W.L. 1932. Effectiveness in nature of the so-called
protective adaptations in the animal kingdom, ohiefly as
illustrated by the food habits of nearctic birds.
Smithson. Misc. Coll., 85(7 )11-201.
Martin, A.C. 19^9* Procedures in wildlife food studies.
U.S. Dept. Int. Wildlife Leaflet No. 325» 10 p.
Martin, A.C., R.H. Gensch, and C.P. Brown. 19^6. Alternative
methods in upland gamebird food analyses. Jour. Wildlife
Mgmt., 10(1)*8-12.
Martin, A.C., H.S. Zim, and A.L. Nelson. 1951* American Wild
life and Plants. McGraw-Hill Book Co., Inc., New fork, 500 p. Massey, A.B. 193d. A yards tick for measuring the habitat of ths
bobwhits quail. Trans. N. Assr. Wildlife Conf., 3*782-786.
Phillips, J.F.V. 1931* Quantitative ssthods in ths study of
nusbsrs of tsrrsstrial animals in biotio oosmunitiss: a
review with suggsstlons. Ecology, 12(4):633-649.
Quay, T.L. 1938. Ths foods and fseding habits of th« savannah
sparrow in winter. Jour. Elisha Mitchell Sci. Soc.,
7*K1)i1-6.
Rand, A.L. 1932. Secondary sexual characters and ecological
eoapetition. Fieldianai Zool., 34(6)t65-70.
Salt, G.W. 1937. Observations on fox, Lincoln, and song spar
rows at Jaokson Hole, Wyoming. Auk, 74(2):258-259*
Steiniger, F. 1937a. Beobaehtungen und Bemerkungen sur Mimikry-
frage. Biol. Zentralbl., 57(1/2)*47-58.
Steiniger, F. 1937b. "Ekelgeschmack" und visuelle Anpassung
einiger Insekten. (Ftitterungsversuche an Vogeln.)
Zeitschr. Wias. Zool. Abt. A., 149(2)s221-257.
Stenger, J. 1958. Food habits and available food of ovenbirds
in relation to territory size. Auk, 75(3)035-346.
Stevenson, J. 1933* Experiments on the digestion of food by
birds. Wilson Bull., 4o(4):155-167.
Stoddard, H.L. 1931* The Bob-white Quail: Its Habits, Preser
vation, and Increase. Charles Scribner's Sons, Inc.,
New York, 559 p.
Testing Agricultural and Vegetable Seeds. 1952. U.S. Dept.
Agr* Handbook No. 30, 440 p., 39 plates. Ticehurst, C.B. 1940. The question of food preferences.
Ibis, Ser. 14, 4(2):337-339.
Walkinshaw, L.H. 1939. Nesting of the field sparrow and
survival of the young. Bird-Banding, 10(3):107-114;
10(4):149-157.
Walkinshaw, L.H. 1944. The eastern chipping sparrow in
Michigan. Wilson Bull., 56(4):193-205.
Walkinshaw, L.H. 1945. Field sparrow, 39-54015. Bird-Banding
16(1):1-14.
Warr«n, b.H. 1690. Report on the Birds of Pennsylvania, with
Special Reference to Food Habits. Penn. State Board Agr.,
Harrisburg, 260 p.
Weed, C.M. 1898. An observation on the feeding habits of the
chipping sparrow. New Hampshire Col. Agr. Expt. Stat.
Bull. No. 55, p. 101-110.
Weed, C.M. and N. Dearborn. 1903* Birds in Their Relations to
Man. J.B. Lippincott, Inc., Philadelphia, 3&0 p.
Wellington, W.G. 1957. Individual differences as a factor in
population dynamics: The development of a problem.
Canadian Jour. Zool., 35(3)*293-323*
Wolcott, G.N. 1937. An animal census of two pastures and a
meadow in northern New York. Ecol. Monog., ?(l):l-90. AUTOBIOGRAPHY
I , D o a n Gsorge Dillery, was born in Present, Ohio, Novesber i d , 1 9 2 8 . I received ny secondary sohool education in the public
•choola ot Fostoria, Ohio, and ay undergraduate training at
Ohio Stato Unitereity, which granted ae the Bachelor of Science d e g r e e i n 1 9 5 2 . The Ohio Departient of Agriculture eiployed i b « a s a H o r t i c u l t u r e Innpector during the years 1932 to 195^<
I n 1 9 5 ? O h i o S tate University granted ae the Master of Science d*gra«. tharing the year1955*56, I was a graduate research a s s i s t a n t a t North Carolina State College. In 1956 I returned t o Ohio State University and was a graduate assistant for three y e a r s a h l l * in residence there. I was successively esployed ass V i s i t i n g In stru c to r and Instructor by Ohio lesleyan Univer s i t y and A l b i o n College while conpleting the requirements for t h s dsgraa D o c to r of Philosophy.
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