Feeding Ecology of Sharp-Shinned Hawks Nesting in Deciduous and Coniferous Forests in Colorado

Abstract

Abstract. Feeding ecology of 11 Sharp-skinned Hawk (Accipiter striates) pairs nesting in aspen (Populus tremuloides), conifer (Abies, Picea spp.), and mixed aspen-conifer habitats in southwest Colorado was investigated during 1988-1989. Small birds (x= 20.9 g, SE = 0.8 g) and mammals (X = 41.1 g, SE = 3.3 g) comprised 91 and 9% of 5 13 prey identified at nests that fledged at least one young, respectively. Sixty percent of the birds eaten during the hawks' nestling and fledgling stages were nestlings or fledglings. Accordingly, median mass of birds eaten decreased from 17.4 g during incubation to 12.1 g during the nestling stage. Although more birds were consumed than mammals during all nesting stages (birds = 91 .I%; mammals = 8.9%), the proportion of birds relative to mammals in diets progressively decreased from incubation through fledging. Taxa of birds in the diet were consumed in proportion to their occurrence in the most abundant of three different habitats surrounding nests, whereas some mammalian taxa were consumed in greater proportion than their relative "availability" in these habitats. This suggested that Sharp-shinned Hawks foraged opportunistically for birds, but may have selectively foraged for mammals. Differences in the habits of mammals (e.g., fossorial vs. terrestrial behavior), and hence their relative availability, may explain the apparent selection for certain species of mammals by Sharp-shinned Hawks.

A comparison of avian use of high- and low-elevation sites during autumn migration in central New Mexico

“…Most of the prey species we documented have been reported as Sharp-shinned Hawk prey in previous studies that were focused on breeding or other seasons (Storer 1966, Duncan 1980, Reynolds and Meslow 1984, Joy et al 1994. Typically, thrushes, warblers, and sparrows tend to be numerically important in the diet of the Sharp-shinned Hawk, which is consistent with our results.…”

“…Because of the potential effects of size-dependent escape speeds and maneuverability, it is possible that the size classes of prey Sharp-shinned Hawks selected were more vulnerable to predation than were either larger or smaller birds. We think this possibility also is unlikely, because smaller birds are often more numerically important in the Sharp-shinned Hawk's diet during the breeding season (Joy et al 1994), and maneuverability of both predator and prey is presumably similar at all seasons.…”

“…The reference feather set included 103 feathers from 57 species, representing broad coverage of the potential prey in the area. Some species were missing from the sample, including swifts, swallows, and hummingbirds, and although swallows and hummingbirds are sometimes taken as prey, they do not constitute a large part of the Sharpshinned Hawk's diet (Joy et al 1994). For most species we obtained feathers from two or three individuals to broaden the genetic sampling.…”

DNA Sequencing Reveals Patterns of Prey Selection in Migrating Sharp-shinned Hawks

“…Using nucleotide sequence comparisons (barcodes), we quantified prey selection of actively migrating Sharp-shinned Hawks ( Table 1). Most of the prey species we documented have been reported as Sharp-shinned Hawk prey in previous studies that were focused on breeding or other seasons (Storer 1966, Duncan 1980, Reynolds and Meslow 1984, Joy et al 1994. Typically, thrushes, warblers, and sparrows tend to be numerically important in the diet of the Sharp-shinned Hawk, which is consistent with our results.…”

“…The reference feather set included 103 feathers from 57 species, representing broad coverage ofthe potential prey in the area. Some species were missing from the sample, including swifts, swallows, and hummingbirds, and although swallows and hummingbirds are sometimes taken as prey, they do not constitute a large part of the Sharpshinned Hawk's diet (Joy et al 1994). For most species we obtained feathers from two or three individuals to broaden the genetic sampling.…”