Yesterday, I gazed out the window of my home office during a meeting, watching California quail and house sparrows forage beneath native sumac. Suddenly, the bush seemed to explode, with birds flushing in every direction.
A second later, a Cooper’s hawk deftly landed underneath the shrubbery. It began hopping around attempting to snag one of the remaining quail that hunkered down instead of flushing. But the hawk was just a little too late.
Over the years, I’ve noted more frequent sightings of both Cooper’s and sharp-shinned hawks around the neighborhood. You’ve probably noticed the same thing. Across the United States, these two hawk species – both similar looking and in the genus Accipiter – have increasingly colonized urban areas.
A new paper in the Proceedings of the Royal Society B sought to “identify factors that determine the occupancy, colonization and persistence of Accipiter hawks in a major metropolitan area.” In the course of their study, the researchers from the University of Wisconsin-Madison and Cornell Lab of Ornithology found that in the 1990s Accipiter hawks occupied 26 percent of sites around Chicago. After two decades, they occupied close to 67 percent of sites.
It’s a trend reported (often via citizen science) around the country. And a big part of it is the bird feeder in your backyard.
The Return of Raptors
By the mid-20th century, many raptor species, including Cooper’s and sharp-shinned hawks, had declined precipitously. Direct persecution and pesticides had taken a heavy toll. Decades of protection have caused populations to rebound, leading raptors including accipiters to reclaim habitat.
But as the birds spread, they found a new world: one of growing cities. One might initially conclude that predators would not find this new world to their liking, as it was covered in concrete and buildings instead of forests. And that’s certainly true for many wildlife species.
But, as the researchers note in their recent paper, cities present a mix of habitats, including backyards, parks and golf courses with plenty of space. These “novel ecosystems” provide opportunity for cover and also, often, for ample food supplies.
The researchers documented the spread of the two hawk species in Chicago via observation through remote sensing data and Project FeederWatch, a citizen science initiative that has conservationists record sightings throughout the winter.
Initially, the hawks colonized areas outside the city. But they increasingly spread to more and more urbanized areas. The researchers documented usage of areas defined by what they call impervious features: roads, buildings, sidewalks. The more impervious the area, generally, the less “green” habitat.
Initially, hawks avoided these highly developed zones. But eventually, as long as there was sufficient prey, they colonized even the downtown. Over the past two years, hawks went from the city fringes to occupying much of the metropolitan area.
The researchers hypothesized that reforestation would play a role in hawk recolonization. But it didn’t. In fact, wintering hawks preferred areas with fewer trees, perhaps to better hunt prey.
The Hawk at the Feeder
Bird feeding is a hugely popular urban pastime. More than 40 percent of U.S. households feed their backyard birds.
That creates an abundance of birds, concentrated in specific, predictable areas. A predator’s bonanza.
The researchers found that the predator’s persistence in urban areas was most influenced by abundant prey. Based on citizen science and other research across the country, hawks have taken advantage of the bounty of bird feeders across the country.
Cities are rapidly changing. The novel ecosystems they create are also highly dynamic and, often, poorly understood. Songbirds, like northern cardinals, may even expand their range due to feeders. Then predators recolonize, shifting species behavior and abundance.
The researchers cite studies in England that show the recolonization of Eurasian sparrowhawks in cities caused a dramatic decline in house sparrows as well as other species commonly found at bird feeders. The sparrows had exploded in population due to the free food sources and lack of predators. When the predators returned, it caused an immediate shift in the urban ecosystem. It’s not so different, really, than what happened when wolves were reintroduced to Yellowstone and found a park with an over-population of elk.
The researchers note that similar shifts in prey abundance might be expected in Chicago and other cities. Some studies have found that urban hawks are feeding heavily on European starlings, house sparrows and pigeons – all non-native species – so they could actually reduce competition for native songbirds.
Do bird feeders change migration patterns? At least one study found that sharp-shinned hawks on the East Coast were less likely to migrate due to the abundance of bird feeders.
Research into Urban Ecosystems is Vital for the Future of Conservation
Clearly, research into urban ecosystems is vital for the future of conservation. Understanding how species interact, and how species use new habitats, can help better design parks and refuges. Perhaps endangered animals that many consider incompatible with cities actually could recolonize urban areas if given a chance. After all, 50 years ago no one considered the Cooper’s hawk to be an urban bird.
And let’s not forget a key factor in helping scientists understand urban wildlife: you. The observations you make at your bird feeder, at the city park and along a greenbelt trail help researchers understand novel ecosystems and their wild inhabitants. While your observations may seem anecdotal, when combined with millions of other observers, they add up to a significant data set.
So, yes, you really are seeing more hawks at your bird feeder. Enjoy the show this winter: the restoration of the predator-prey dynamic to the urban wild.
Join the Discussion
Thanks very much for this excellent article that addresses one of the most interesting and uplifting aspects of continued urbanization, the increasing populations of some raptor species. Citizen scientists have contributed significantly to our knowledge of this phenomenon, through eBird and other projects. For further information, there’s been a new book on the topic published in 2018 titled Urban Raptors: Ecology and Conservation of Birds of Prey in Cities.
Yes recently a sharp-shinned hawk nabbed a back-headed bird (junco or black capped chickadee) at my back yard finch feeder in suburban Hawthorne, NJ. The hawk perched by the feeder for quite some time eating its little catch. The feeder was quiet the next few days as though the killing had been witnessed. Now the finches, juncos and others are back.
I have lived in Fraser, CO for 14 years. When I first moved here, Ospreys were few and far between. I only saw them once or twice a year. This passed year I observed at least 4 pairs staying near the same areas around Grand County. Also have seen more Bald Eagles. Something right is happening.
I was wondering why I was seeing more but I notice a decline in American Kestrel Hawk
We have a Coopers Hawk that has made numerous appearances in our yard here in Atlanta over the past couple of months. We have a tiny pond and witnessed him plucking a frog from it and flying away with it this past week. Really fun to watch him. He sits in a dogwood waiting and watching sometimes for 30 minutes or more.
I’m very curious about this photo. The red-shouldered hawk looks as if it could have what falconers in days gone by called “frounce”, or canker, caused by a protist Trichomonas gallinae. Hawks and owls can be infected by eating infected doves and pigeons, or possibly drinking at contaminated fountains! If you look closely at the base of the neck just under the beak, it looks a bit puffy, which might indicate an infection of the esophagus. Just a guess, but I’ve studied this parasite in doves and pigeons many years ago and published a chapter in a textbook, Mourning Doves in North America. Like I said, just curious…
That’s very interesting. I think I have some higher resolution images that might give you a closer look. Let me know if you’d like me to send them your way. Photo was taken in North Florida near St. Augustine last week.
Could be just a full crop!?
Oh, that explains it! I started feeding here in Connecticut three years ago and now see a good number of hawks sitting nearby in trees. Red shouldered, peregrine, one redtail and a few I wasn’t sure of IDs. Witnessed redshouldered pair mating! I have added strips to my windows as one juvenile came straight at it. He flew away okay. Very exciting to see them all! If I lose a songbird or two, it’s okay, I have plenty.
Just had a 1syt sitting in a bush outside our kitchen window by the feeders & bath
This is good news! However one concern is the evidence that bird hunters like Accipiter are increasingly at risk of secondary poisoning from rodenticides in the city and suburbs. Normally they would not take rats, but are tempted by easily caught rats affected by rodenticides. See recent research by Mike Lohr.
Also urban peregrines affected by poisoned pigeons in Melbourne Australia. We have got to stop this massive use of cheap poisons!
We know there are red tail hawks in our neighborhood. Sunday, 12/30/18 I called my husband to the back slider because there was a lone bird, back to me, sitting on a wall, and NO other bird activity in sight. Size alone makes me peer through the binoculars. My husband and I agreed, yep, a hawk. It flew away and the usual sparrow, finch, pine siskin, scrub jay, California quail appear. (Along with the pigeons that I scarecrow away) Today, 1/3/19, I backed out of my driveway and water was flowing down the gutters. As I tried to see where it was coming from (probably a frozen pipe burst) I saw a juvenile hawk drinking water from the overflow (around the corner and up the street, water was flowing from a backyard hose.) I love feeding and watching my backyard birds in Reno, NV! Thanks!