Anyone who keeps a bird feeder has likely had the same uneasy thought after seeing a sudden blur of wings in the yard: What was that hawk doing here?
A University of Kentucky Martin-Gatton College of Agriculture, Food, and Environment (CAFE) study helps answer that question. The work, "Citizen science provides an unprecedented glimpse into the diets of Astur cooperii (Cooper's hawk) and Accipiter striatus (sharp-shinned Hawk)," was led by researchers in the Department of Forestry and Natural Resources (FNR) and published in Ornithology.
Citizen science is the public's voluntary participation in scientific projects, collaborating with experts to collect, analyze or report data.
Using thousands of photos shared through the citizen science platform iNaturalist, the authors took a closer look at the diets of two common hawks often seen around neighborhoods, feeders and wooded areas: The Cooper's hawk and the sharp-shinned hawk. The study found both species are mainly hunters of other birds, filling an important gap in what scientists know about two raptors many people see but few fully understand.
"We were very excited to explore the opportunities citizen science provides to the field of wildlife research, especially for two common backyard birds," said Will Gibson, a first-year graduate student in FNR who helped lead the study. "Citizen science platforms like iNaturalist offer an incredible glimpse into the lives and behaviors of wildlife that may otherwise be understudied."
The team reviewed 74,974 photographs of the two hawk species and identified thousands of predation events, yielding an unusually large dataset across much of the birds' range.
"This is filling in an important gap in what we understand about these very common backyard birds," said Darin McNeil, Ph.D., assistant professor of wildlife management at Martin-Gatton CAFE. "There's a lot of information out there from citizen scientists that had not really been analyzed in this way, and we were able to use that to learn what these hawks are actually choosing to eat."
That matters to birdwatchers and homeowners, especially those who spend time watching activity around backyard feeders. Cooper's hawks and sharp-shinned hawks are not coming for seed; they are coming for the birds that gather there.
"If you see one of these hawks in your yard, you can be pretty confident it is scoping out the bird feeder and looking for a meal," McNeil said.
The two hawks look a lot alike, though the sharp-shinned hawk is smaller. That size difference turns out to matter.
Study results
The study found that Cooper's hawks, the larger of the two, strongly favor birds and especially larger prey such as doves and pigeons. The research showed they selected rock pigeons, mourning doves and other dove species more often than would be expected based on what was available. They also regularly ate mammals, but birds were still the clear preference.
Sharp-shinned hawks were even more focused on birds. In the study, nearly every identifiable prey item for that species was a bird. European starlings, mourning doves and house sparrows were among the most common prey, and the researchers found only one mammal record for the species in the dataset.
"We were actually surprised by how bird-focused the sharp-shinned hawk was," McNeil said. "There are reports in the literature of them eating mammals, but in our data we found almost no evidence for that."
The findings support a long-held idea that both hawks are avian specialists, meaning they mostly hunt birds. The study also showed that prey size differed between the two species. The prey eaten by Cooper's hawks averaged 166 grams, while prey eaten by sharp-shinned hawks averaged 59 grams.
The reasons may be practical. McNeil said doves are especially attractive prey for Cooper's hawks. They are large, provide a good meal and are often out in the open. They are also less able to fight back once caught than some other birds.
"If you're a dove, you are in a rough spot," McNeil said. "They're fat, they're often exposed, and they don't have many defenses once a hawk grabs them."
The study's chart of preferred prey showed rock pigeons standing out for Cooper's hawks, and European starlings ranked high for sharp-shinned hawks. Mourning doves also appeared high on the list for both species.
The importance of citizen science
The project also highlights the growing value of citizen science. Researchers downloaded iNaturalist records, then examined them one by one to see whether a hawk was holding prey and, if it was, what kind of animal it had caught.
The team used expert help to identify hard-to-recognize prey from feathers, fur and other visible clues. They also compared those hunting records with background observations of birds, mammals and reptiles to see not just what hawks ate, but what they seemed to prefer.
That approach gave researchers a broader view than older studies that focused only on nests or bird feeders. It also helped them see prey that might not often appear in feeder-based projects, such as pigeons.
"These are native birds of prey that belong here," McNeil said. "They are part of the natural system and part of keeping other animal populations in check."
The research also points to another change people may already be seeing. Cooper's hawks have become more common in suburbs and urban areas over recent decades. McNeil said that shift is one reason these citizen scientists are noticing them more often at feeders and in neighborhoods.
"By expanding the types of data that can be garnered from citizen science, we have shown how useful citizen science is as a tool," Gibson said. "This just shows how important everyday people are to the field of wildlife research."
This material is based upon work that is supported by National Institute of Food and Agriculture, U.S. Department of Agriculture, McIntire-Stennis Capacity Grant under award number KY009043. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the Department of Agriculture.
