Food Habits of Savannah and Grasshopper Sparrows in Relation to Foods Available
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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