Who’d have thought?
Turns out the Cooper’s hawk — the swift and storied hunter of forest and woodland — is a city fan at heart.
Drawn by the birds that are drawn to birdfeeders, this crow-sized predator is doing exceptionally well throughout the Twin Cities and even the starkest of American urban environments. This is a sweeping change from the 1960s and ’70s when the Cooper’s population was scarily low throughout much of the nation due to shooting, habitat loss and reduced nesting success from a now-banned insecticide.
“It’s an amazing story of unintended consequences,” said Robert Rosenfield, one of the world’s leading Cooper’s hawk experts and a professor at University of Wisconsin-Stevens Point. “Peoples’ interest in feeding and watching birds in their own backyard attracted the very predator that eats them. Cooper’s have flourished because urban prey is so abundant.”
This irony is documented in a newly published study by University of Wisconsin-Madison researchers Benjamin Zuckerberg and Jennifer McCabe. Their research focused on the city of Chicago. It is based on more than 20 years of citizen science gathered by Project FeederWatch, a Cornell Lab of Ornithology and Bird Studies Canada collaboration in which people who feed birds document avian activity.
“These forest birds have colonized urban America at an amazing speed, and we documented that in Chicago,” said Zuckerberg. “In the late 1990s, Cooper’s and sharp-shinned hawks occupied only 26 percent of the sites around Chicago. Today, it’s about 70 percent. Like coyotes, cougars and certain other top predators, they have adapted to the ever-growing urban environment.”
Zuckerberg said before the study he and McCabe suspected impervious surface (roads, parking lots, buildings) would influence hawk populations. So, too, they thought, would the amount and location of preferred tree canopy. But that wasn’t the case. “Initially hawks colonized areas of less development, but over time it was food availability, meaning backyard birds, that was the single most important factor,” McCabe said.
The Cooper’s hawk prefers hearty meals — robins, jays, doves and the like — but once established in an urban area any old chickadee dinner will do.
“Prey biomass wasn’t an important driver of colonization or persistence,” McCabe said. “Perhaps hawks are cuing in on sheer numbers of birds and not a particular species.”
The Chicago research parallels what Carrol Henderson, a noted Minnesota bird expert, has seen in the Twin Cities. “When I began Minnesota’s nongame wildlife program in the 1980s, retailers sold bird seed only in winter,” he said. “In fact, I was able to talk retailers into donating their unsold stock for use at birdfeeders at state parks and highway rest areas rather than letting it go to waste from eventual spoilage.
“As interest in bird feeding grew in the 1990s and early 2000s and so did the number of special seed mixes that attract more and higher value birds in all seasons. Today, the prevalence of urban Cooper’s and sharp-shinned hawks reflects the fact that bird feeding is a popular year-round hobby and $4 billion a year business.”
Crashing the party
Dr. Julia Ponder, executive director of the University of Minnesota’s Raptor Center, has also seen Cooper’s hawk numbers climb. She said Cooper’s, along with owls, bald eagles and red-tailed hawks, are the most common birds treated at the center. “Years ago Cooper’s were a midlevel admission,” she said.
Lori Naumann of the Minnesota Department of Natural Resources nongame wildlife division, who responds to many hawk inquiries, counsels homeowners to take down a bird feeder for a few weeks if they don’t want Cooper’s crashing the feeder party. Typically, she said, urban hawks will move elsewhere if prey isn’t abundant.
“People who want to help songbirds can add a brush pile to their backyard to provide natural protective cover,” Naumann said. “Cooper’s are perch-and-scan hunters. They patiently sit on a branch, then swoop in for a meal. It’s often easy pickings because so many backyards are mostly lawn and tall trimmed trees, which means long sight lines and few obstacles in flight.”
Though some folks don’t try to understand hawks, Zuckerberg said their presence represents an opportunity to connect the disconnected to nature. “Hawks are cool,” he said. “They are part of a compelling prey and predator drama that unfolds each day outside kitchen windows all across America. People can engage in this by simply watching or being part of the FeederWatch program.”
Zuckerberg added that understanding how wildlife species adapt to urban environments is important because the United States is adding an estimated 1 million acres of urban landscape per year.
“The more we learn about urban habitat, colonization and persistence the better we can manage wildlife in an ever-developing world,” he said.
Rosenfield, the Stevens Point professor, offered a similar sentiment, saying “we need to know more about the relationship between bird-feeding and top predators.” He said Cooper’s hawks have become the most common backyard breeding bird of prey in North American, yet there is no evidence to indicate the species is depressing songbird populations. The hawk, he said, may be negatively affecting bobwhite quail and redheaded woodpeckers in some parts of the country.
“I envy anyone who has a Cooper’s in the backyard,” he said. “It used to be a forest bird. Now it isn’t. Those who see songbirds scatter at the feeder are witnessing a remarkable comeback story.”
C.B. Bylander is a freelance writer. He lives near Baxter, Minn.