Merlin Pair Nesting in New York Feeds Primarily on Swallows

Abstract

We conducted a detailed study of prey selection by a breeding pair of Falco columbarius (Merlin) on the Wells College campus in central New York. We identified prey from corpses and feathers (110 positive identifications from 112 prey items). Of the 16 prey species, swallows (35 Hirundo rustica [Barn Swallow], 7 Tachycineta bicolor [Tree Swallow], and 4 Stelgidopteryx serripennis [Northern Rough-winged Swallow]) predominated, comprising 41.8% of prey items (estimated 29.9% of biomass). Barn Swallows and Passer domesticus (House Sparrow) were the 2 most common species taken, both appearing throughout the nesting period (31.8% and 19.1% of prey items, respectively). As the season progressed, the proportion of juveniles taken increased to 90% by the latter half of July. We observed the female consuming the heads of freshly killed prey before plucking and delivering the food item to nestlings on 4 occasions, and we recovered 5 headless corpses of Merlin prey. We never found discarded heads of prey. These observations are in contrast to reports that Merlins typically discard the heads of prey. We propose nutritional explanations for selective consumption of the heads of prey by predatory birds. Five young fledged from our study nest, indicating high reproductive success. Our report of successfully breeding Merlins feeding principally on swallows is unique, and shows that the dietary emphasis on swallows did not compromise reproduction. Our results illustrate the flexibility of Merlins to local prey availability and reinforce the vulnerability of avian prey in open areas to Merlin predation.