Determinants of predation risk in small wintering birds: the hawk’s perspective

Abstract

The small-bird-in-winter paradigm is prominent in the field of behavioral ecology. However, our conceptual understanding of this paradigm is limited by our lack of knowledge about Accipiter hawks. Although Accipiters are the major predators of small wintering birds, we know little about their behavior during the winter. In this paper, we present the first description of the predatory behavior of wintering sharp-shinned hawks (Accipiter striatus), focusing on their selection of prey and attack strategies. We also relate basic prey behavior to the risk of death during an attack. During the winters of 2000–2004, we observed 255 attacks and recovered 112 prey items from 21 intensively radio-tracked hawks. The diet of sharp-shinned hawks in the study was composed primarily of sparrow-sized prey, intermediate-sized starlings (Sturnus vulgaris), American robins (Turdus migratorius), and the occasional larger prey such as mourning doves (Zenaida macroura). Both sexes killed all sizes of prey, although female hawks took significantly more large prey than did males. Small preys under 20 g, such as parids, were largely ignored. This lack of very small prey in the diet of sharp-shinned hawks suggests that we might focus the small-bird-in-winter paradigm on sparrows and intermediate-sized prey, such as robins, as the main prey base of Accipiters at least in North America. In addition, solitary and feeding prey were significantly more likely to be captured during an attack than prey in groups and those not feeding. Our hawk-driven observations provide rare empirical support for the concept that flocking birds are safer than solitary birds and alert birds experience less risk than those preoccupied with feeding.