8/6/2023 0 Comments Hawks eating birds“In some ways our quiz was testing a worst-case scenario,” said Miller. The researchers used this information to re-run their analyses and found that even with these misidentification rates, the overall pattern with Sharp-shinned focusing on smaller birds and Cooper’s Hawks on both smaller and medium to larger birds stayed the same. Respondents identified Cooper’s Hawks as Sharp-shinned Hawks 18% of the time and Sharp-shinned Hawks as Cooper’s Hawks 27% of the time. Miller used photos from the Macaulay Library to quiz FeederWatch participants and expert birders to see how frequently each group might misidentify raptors. “Although Sharp-shinned certainly can be found in urban areas, particularly in the winter, they are often found in forests,” said Miller, “and the cool thing is that we were able to see that in their preferences for prey that also frequently occur in forests, such as Evening Grosbeaks and Purple Finches.” Cooper’s Hawk preying on a Red-bellied Woodpecker © Dave Spier / Macaulay Library 107217651Įven though Cooper’s and Sharp-shinned Hawks are notoriously difficult to distinguish, Miller and colleagues found that their results held up even if some observers may have made an error in identifying the hawks. Interestingly, Miller and colleagues also found that what they eat is reflected by their habitat preferences. Still, no one has studied predator preferences at this spatial scale before, so to see such a strong result speaks to the power of citizen scientists to document these patterns,” said Miller. “Cooper’s Hawks are increasingly common in urban areas and they are bigger, so their focus on larger prey, such as pigeons, isn’t necessarily surprising. Miller explains that a focus on different size prey may be one component that allows these species to coexist. Cooper’s Hawks also took smaller-bodied birds, but they mainly took medium and larger-bodied birds, such as European Starlings and pigeons. Miller and colleagues found that Sharp-shinned Hawks took smaller-bodied birds, such as juncos and Pine Siskins most often. Prey available for these raptors consisted of greater numbers of small-bodied birds, such as Pine Siskins, with fewer medium-sized birds, such as jays, and still fewer larger-bodied birds, such as quails. That meant we could figure out the preferred prey of Cooper’s and Sharp-shinned Hawks, because we had data on who was eating who and we had data on prey availability.” Sharp-shinned Hawk © Ian Routley / Macaulay Library 446889041įrom October 2015 to April 2022, FeederWatchers observed 1,186 incidences of Cooper’s Hawks eating a bird at their feeders and 677 incidences of a Sharp-shinned Hawk eating a bird. “A few years ago,” Miller said, “we created an option for FeederWatchers to tell us not only which birds were at their feeders, but how those birds were interacting with one another. New research in the Journal of Avian Biology set out to better understand if these similar raptor species evolved to select different prey and to compare how the availability of prey might shape their choices.Įliot Miller, collections manager at the Macaulay Library at the Cornell Lab of Ornithology, and colleagues took advantage of data collected by citizen scientists for Project FeederWatch to answer this question. These two bird-eating raptors co-occur throughout much of North America, but given their similarities, a common question often emerges-how do they coexist? A central tenet in ecology suggests that when two ecologically similar species co-occur, competition should drive one or both to take advantage of different niches, for example by eating different prey. And every once in a while, a Cooper’s Hawk or a Sharp-shinned Hawk might fly in and stir things up. Watching chickadees and finches jostle at your feeder provides countless hours of entertainment. What’s For Dinner? Sharp-shinned and Cooper’s Hawks Pick Different Foodsīy Kathi Borgmann Cooper’s Hawk © Michael Kerwin / Macaulay Library 405390081
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