City birds retain their fear of hawks

By Joshua Rapp Learn

A Cooper's hawk. Credit: Renee Grayson

Have urban birds lost their ability to rough it due to the comforts of city living?

Researchers wanted to learn more about urban bird behavior, but they needed help.

“How do species maintain some of these natural relationships they have with other species, and are those dynamics altered in habitats where there are a lot of people?” wondered Benjamin Zuckerberg, a professor in the forest and wildlife ecology department at the University of Wisconsin-Madison.

Zuckerberg and his colleague tapped into Project FeederWatch—a program run by the Cornell Bird Lab and Birds Canada that elicits citizen scientists to survey birds at their backyard feeders. For a study published recently in Ecology and Evolution, they sent speaker equipment to volunteer participants in Chicago that would play back the calls of Cooper’s hawks (Accipiter cooperii), a common predatory bird in the city.

For two winters at 15 sites in the city, the volunteers remotely activated the hawk call speakers when birds were visiting their feeders. The citizen scientists dictated their observations about behavior on a recording device for five minutes before the call, for five minutes during the call, then for another five minutes after the call stopped. When there was more than one bird at their feeder, the volunteer would split the five minutes up into 30-second periods, describing individual birds’ activity one at a time. They then sent their observations to Zuckerberg and his colleagues.

The participants observed different types of behavior while conducting their experiments. When birds heard the hawk calls, some birds fed less and grew more vigilant. Others would fly away, and some would freeze.

Black-capped chickadees (Poecile atricapillus) often send up an alarm when they perceive a predator. “Chickadees will make a very specific alarm call—other species will cue into that as a threat,” Zuckerberg said, and they wanted to see if these sentinel interactions persist.

The researchers found that the urban and suburban birds still reacted to the potential threat of raptors in Chicago.

“For the most part, these antipredator behaviors were maintained,” Zuckerberg said, though he noted that they saw no evidence of the sentinel effect from chickadee calls.

Bigger bodied birds that hawks often target more, such as mourning doves (Zenaida macroura), rock pigeons (Columba livia) and European starlings (Sturnus vulgaris) were a little more vigilant than smaller birds when they heard the playback.

Zuckerberg said that while cities clearly affect the way birds behave, this research shows that they maintain some of their natural responses to predators.

The study also shows that citizen scientists can be relied on to help gather more complex research data.

“We can expect even more out of our public being engaged in these community science projects,” he said.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society. Contact him at jlearn@wildlife.org with any questions or comments about his article.

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