Nav: Home

Woodland hawks flock to urban buffet

November 06, 2018

MADISON, Wis. -- For the nearly 35 million Americans who faithfully stock their feeders to attract songbirds, an increasingly common sight is a hawk feeding on the birds being fed.

Now, in a new study published Nov. 7, 2018, in the Proceedings of the Royal Society B, a team of Wisconsin researchers documents that woodland hawks -- once in precipitous decline due to pollution, persecution and habitat loss -- have become firmly established in even the starkest urban environments, thriving primarily on a diet of backyard birds attracted to feeders.

According to the researchers, the birds are doing so well that an increasing number of rural woodland hawks are, in fact, city-bred.

"Top predators are beginning to use urban areas more frequently and establish breeding populations, and hawks are a nice example of this," explains Benjamin Zuckerberg, a University of Wisconsin-Madison professor of wildlife ecology and a senior author of the new study. "For hawks, the secret is out: There is a hyperabundance of prey" in the city.

The availability of food -- in this instance, backyard birds -- is the single most important factor in drawing avian predators such as Cooper's and sharp-shinned hawks to the city, says Jennifer McCabe, a UW-Madison postdoctoral fellow who led the new study.

As pesticides such as DDT were curbed and new protections from human hunters came into play beginning in the 1960s, populations of woodland avian predators like Cooper's and sharp-shinned hawks have soared. As populations rebounded, hawks began to move into urban areas and the study concludes that, at least for Chicago, prey availability at feeders significantly influenced colonization and persistence in the city, explains McCabe.

While the new study uses Chicago as its laboratory, the phenomenon of top predators establishing themselves in urban environments is a global trend, say the Wisconsin researchers.

"Across the world stories are popping up about predators expanding into cities," says McCabe. "Bear and cougars in the U.S., leopards in India, and red foxes in Europe, to name a few."

The new study depended on more than 20 years of citizen science data gathered by participants in the Cornell Lab of Ornithology's Project FeederWatch, where people who feed birds document avian activity in their backyards.

"Project FeederWatch is the perfect program for this kind of research because you can use that information not only to document hawks, but also their prey," says Zuckerberg of the landmark citizen science project.

Quintessential woodland predators, Cooper's and sharp-shinned hawks are what wildlife biologists call "perch and scan" hunters, sitting quietly on a tree branch and swooping in when a meal comes within striking distance. "Bird feeders," says Zuckerberg, "are like buffets. It is an easy meal."

The new insight from the Wisconsin study is that for the hawks it is all about food. Once established in cities, the urban environment and the absence of trees made little difference.

"I was surprised that tree canopy cover was not important in colonization by these woodland hawks," McCabe says. "However, they aren't nesting in the winter, meaning they are more concerned about their own survival and not raising young. So it makes sense that food availability would be so important."

Using 20 years of Project FeederWatch data from 1996 to 2016, McCabe and her colleagues portray a steady advance of the predators from outlying rural areas to the hardened center of Chicago, a pattern that also occurs in many other North American metropolitan areas and also in Europe, where sparrow hawks have aggressively colonized urban landscapes.

One other surprising finding, according to McCabe and Zuckerberg, is that prey size did not seem to be an important factor. The informed assumption, says McCabe, was that larger prey would be preferred menu items for the hawks.

"Prey biomass wasn't an important driver of colonization or persistence," she notes. "Much of the literature states, at least for Cooper's hawks, that they prefer larger-bodied prey like doves and pigeons. Perhaps these hawks are cueing in on the sheer number of birds and not particular species."

An important take-home message, says McCabe, is that cities, which in the United States are adding an estimated 1 million acres of urbanized land each year, are increasingly important wildlife habitat: "Don't discount urban areas as habitat. The more we know about which species and what landscape factors allow those species to colonize and persist in urban areas, the better we can manage wildlife in an ever-developing world."
-end-
CONTACT: Jennifer McCabe, jmccabe4@wisc.edu; Benjamin Zuckerberg, (608) 262-8879, bzuckerberg@wisc.edu

Terry Devitt, (608) 262-8282, trdevitt@wisc.edu

Funding for this research was provided through NASA's Citizen Science for Earth Systems program (grant no. NNX17AI68A).

University of Wisconsin-Madison

Related Predators Articles:

Marine predators: Bigger in size with an appetite to match
The size of marine invertebrate predators has increased over the past 500 million years, while the size of their prey has not, a new study reveals.
Predators are real lowlifes
By deploying green clay caterpillar models across six continents, researchers unmasked an important global pattern.
Fish step up to lead when predators are near
Researchers from the University of Bristol have discovered that some fish within a shoal take on the responsibilities of leader when they are under threat from predators.
Restoring predators and prey together speeds recovery
Restoring predator and prey species together helps accelerate ecosystem recovery efforts compared to pursuing restoration of one species at a time, new research concludes.
Recovering predators and prey
Researchers show how simultaneously restoring predators and prey is much faster and more effective than doing so one at a time.
Reducing pressure on predators, prey simultaneously is best for species' recovery
Reducing human pressure on exploited predators and prey at the same time is the best way to help their populations recover, a new study indicates.
When it comes to predators, size matters
When it comes to predators, scientists find larger sheephead that consume bigger urchins help keep that population under control.
Birds of a feather flock together to confuse potential predators
Scientists from the universities of Bristol and Groningen, in The Netherlands, have created a computer game style experiment which sheds new light on the reasons why starlings flock in massive swirling groups over wintering grounds.
For viral predators of bacteria, sensitivity can be contagious
Scientists have shown for the first time how bacteria with resistance to a viral predator can become susceptible to it after spending time in the company of other susceptible or 'sensitive' bacteria.
How miniature predators get their favorite soil bacteria
Tiny predators in the soil can literally sniff out their prey: soil bacteria, which communicate with each other using scent.

Related Predators Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...