Prey Selection by Big Brown Bats (Eptesicus fuscus) and Common Nighthawks (Chordeiles minor)

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Abstract
I compared the diets of big brown bats (Eptesicus fuscus) and common nighthawks (Chordeiles minor) with the insect prey available as sampled using a whirligig trap. Because both species forged at the same place and overlapped temporally in their foraging periods, I predicted that the diets would be the same for both species. Trichopterans over 5 mm in body length were the most important prey item for both bats and birds, constituting at least one half of the diet in terms of frequency. Hymemopterans and coleopterans were eaten by C. minor in proportions greater than expected on the basis of availability, while E. fuscus occasionally ate more coleopterans and dipterans than would be expected. The bats showed no preference for, or avoidance of, hymenopterans. Neither species ate chironomids even though these insects constiuted at least 60% of the available prey items. I conclude that the apparent prey selection by nighthawks and bats is not opportunistic in nature, but may reflect constraints of prey detection.