Feeding Ecology of Three Resident Sympatric Sparrows in Eastern Texas

THE feeding ecology of two or more closely related organisms involves detailed observations of those organisms in their natural habitat.Of particular interest are ways in which competition for food is reduced between them.Moreau (1948) stated that whenever related species of birds overlap in range, they are either different in size or they use different methods of seeking food.Lack (1945) found that the sympatric Great Cormorant (Phalacrocorax carbo) and Shag (Phalacrocorax aristotelis) coexist by specializing on different foods.MacArthur (1958) and Morse (1973) reported that competition between closely related warblers was reduced, in part, by differences in vertical and horizontal feeding positions and behavior.Wiens (1969), in a study of seven grassland birds, and Hespenheide (1971), in a study of three eastern deciduous forest flycatchers, found preferences in habitat based on foliage density that would lead to a spatial distribution, thereby reducing competition for food.The purpose of this study was to investigate the foraging behavior and food habits of the sympatric Bachman's Sparrow (Aimophila aestivalis), Field Sparrow (Spizella pusilia), and Chipping Sparrow (Spizella passerina) that have allowed them to coexist as permanent residents in eastern Texas.METItODS AND MATERIALS Field data were collected from 1 July 1971 to 29 February 1972, on two study tracts in Nacogdoches County, Texas.Field equipment consisted of a pair of 8 X 35 binoculars, a clipboard with data sheets, and a folding aluminum chair.Observations were divided into summer (July and August), fall (September, October, and November), and winter (December, January, and February) seasons.An average of 15 h a month was spent in each study tract.Most observations were made during the first 4 h after sunrise.A total of 250 h was spent in the field.Study tracts.--Studyareas were located 14.3 km southwest (area I) and 6.5 km north (area II) from the junction of Highways 21 and 59 in Nacogdoches, and consisted of 10 and 8 ha, respectively.Area I was grazed land supporting an open stand of pine with a few hardwoods and a partial clearing with a small stock pond.Area II was an old brushy field with scattered bushes and small hardwoods, junipers, and pine trees.The tree composition on area I was loblolly pine (Pinus taeda) and shortleaf pine (Pinus echinata), 79% (combined); persimmon (Diospyros vrginiana), 7.5%; eastern red cedar (Juniperus virginiana), 6.5%; post oak (Quercus stellata), 3.5%; and sassafras (Sassafras albidum), 3.5%.Greenbriar (Smilax sp.) was abundant in certain areas.Some of the common grasses were little bluestem (Schizocharium sp.) and panicurn (Panicurn sp.).