Foraging Ecology and Diet Selectivity of Tree Swallows Feeding Nestlings

We studied the foraging ecology of a population of Tree Swallows (Tachycineta bicolor) breeding in New York State over a period of 5 years. While feeding nestlings, adult Tree Swallows tended to spend most of their time within sight of their nest box and less than 12 m above the ground. Major insect taxa captured include Diptera, Hemiptera, and Odonata, ranging in length from mainly 0-10 mm, with some individuals up to 60 mm. The sex of the parent delivering the food had no significant effect on diet composition. Selection for or against food categories was determined by comparing the proportion of insects of different types in the diet of Tree Swallows to the proportions available in the air column. Tree Swallows showed consistent selection for insects larger than 3 mm and against smaller insects, especially Diptera in the suborder Nematocera. Only minor differences in diet were observed among years, and the effects of the abundance of food available were generally small. The patterns of selectivity found in this population were consistent with those found in previous studies on this species carried out in other locations, and these patterns are likely the result of differences in the profitability or visibility of prey types.