Once found predominantly in rural woodlands, hawks have come to find a convenient home in cities, according to a study led by UW-Madison researchers.
Woodland hawk populations were once declining in the face of habitat loss, pollution and persecution but are now rebounding. The predators are adapting to urban landscapes, which happen to provide ample and predictable food sources.
Predatory birds such as Cooper’s and sharp-shinned hawks find an overabundance of prey to feast upon when they move to cities, postdoctoral fellow Jennifer McCabe said. Smaller birds are drawn to backyard bird feeders, creating a reliable hunting ground for the hawks.
In cities such as Madison, urban hawks are also a cause for increased vigilance among residents who like to let their backyard chickens free range. In one East Side neighborhood that’s home to multiple flocks, a pair of Cooper’s hawks took up residence last summer, raising and teaching their young to hunt amid chickens forced into lock down.
The UW-Madison-led study looked at data collected over 20 years across Chicago and some of its surrounding suburbs through Project FeederWatch. Project FeederWatch is an annual data collection program that runs from November through April in which participants intermittently count the species and numbers of birds that visit the bird feeders at their homes.
The study determined the likelihood that a Cooper’s or sharp-shinned hawk would occupy any site within a city during each year. In Chicago, the likelihood jumped from about a 35 percent chance in 1996 to a 60 percent chance in 2016. Other cities, including Atlanta, Boston and Denver, also saw increases.
Studying the trends of predators in urban areas allows scientists to see the effects that urbanization has on animals and how those animals adapt — or don’t adapt — to the man-made environment.
Cooper’s and sharp-shinned hawks are known to eat medium- to large-sized birds, such as mourning doves or European starlings, so McCabe said her team expected the size of the prey in any given area would affect the hawk population. Instead, the researchers found that hawks aren’t very picky eaters — they’re more than willing to eat smaller birds if there are enough of them.
“It doesn’t matter if (the birds are) the species desired, but it does matter that there’s a lot of them,” McCabe said.
Researchers have seen anecdotal evidence of predators in most urban areas, said Benjamin Zuckerberg, a professor and researcher at UW-Madison who worked on the study. McCabe said everything from bears to mountain lions even to leopards in India have found ways to survive in urban areas.
“It’s a global phenomenon at this point,” Zuckerberg said.
Red foxes in Europe have started relying on food waste from humans, and about 87 percent of an urban leopard’s diet is domesticated animals, according to the study.
Although Madison itself wasn’t a point of study, both Zuckerberg and McCabe said it’s likely the same hunting trends are happening here.
“Every city has seen an increased chance it would be occupied by hawks,” McCabe said.
Hawks typically perch and wait to ambush their prey, so the birds in Chicago — and likely other cities — can post themselves near a feeder where they can reasonably expect numerous birds to be flying to and fro.
McCabe and her team also expected the amount of green space in a city and the tree canopy to be important factors in a hawk’s decision to stay in urban areas, but the amount of tree coverage was not a deal breaker for hawks.
“They were able to persist in what would have been an inhospitable environment,” Zuckerberg said.
Even though urban areas that are feeding grounds for smaller birds have become hunting grounds for predators, many of those small birds have retained their natural instincts that protect them from predators. McCabe said that when FeederWatch participants played predatory bird calls near feeders, the small birds knew to flee.