Variation in nestling provisioning behavior in Acadian flycatchers (empidonax virescens) /

Abstract

Acadian Flycatchers (Empidonax virescens) at the Ravenna Training and Logistics Site in northeast Ohio were observed to detennine if prey choice affects reproductive success. Arthropods fed to nestlings by specialist pairs (n=3 nests) and generalist pairs (n=5 nests) were identified using videotaped feedings of 7, 8, 9 and 10 day old nestlings. Specialists were classified as adult pairs for which 50% or more of the prey fed to nestlings consisted of a particular order or arthropods. Prey quality was detennined by size, with each food item being classified as small (0 - 5 mm), medium (>5 - 10 mm), or large (> 10 mm). Nestlings were weighed at 10 days of age as a measure of reproductive success. For 4,727 feeding attempts, 1,715 (36%) prey were identified to order and 3,633 (77%) prey were sized. The predominant arthropods in the nestling diet were Dipterans (45%), Lepidopterans (21 %), Hymenoptera (8%) and Phalangida (7%). Specialists tended to feed young less often than generalists, yet there was no difference in average nestling weight between specialist nests and generalist nests. Specialists fed prey from 5 - 9 orders whereas generalists fed prey from 7 - 11 orders. Specialists fed more large prey to nestlings and generalists fed more small and medium prey to nestlings. Therefore, it appears that the quality of prey may be more important than the quantity of prey fed to nestlings. In addition, specialists tended to spend more time at the nest when feeding, which would be adaptive for nest defense. These results suggest that a benefit of being selective may be a reduced risk of predation at the nest.