Study finds peregrine falcons mate for life, even in the city

In the wild, peregrine falcons build isolated nests within tall cliffs and the birds are known to mate for life.

Twenty-five pairs of peregrine falcons now reside in the bridges and buildings of Chicago, and despite so many birds living in such close proximity to each other – the birds of prey still appear to maintain their fidelity, according to a new study in the journal PLOS ONE.

“Peregrine Falcons that now live in the Chicago region are living in very different conditions than you’d normally see for these birds, so we wondered if the falcons’ mating habits had changed too,” study author John Bates, an associate curator of birds at The Field Museum in Chicago, said in a news release. “Each spring this population also has migratory peregrines passing through on their way to all parts of Canada, so we didn’t know what we were going to find, but it turns out that almost all of the mated pairs in the city remain monogamous through the years.”

Coming back from the brink

Peregrine falcons almost became extinct in the US in the middle of the 20th century as a result of thinning in their eggshells brought on by the pesticide DDT, as shown in egg collections at the Field Museums. The pesticide was eventually banned.

Reintroduction programs have made it possible for peregrine falcons to come back throughout the Midwest, with populations thriving in both rural and urban areas. Ninety percent of the mating pairs in the Midwest make their homes on buildings and bridges in the greater Chicago area.

To figure out if these mating pairs in Chicago stay devoted to each other, the researchers used a mixture of field observations and DNA evaluations. The Chicago Peregrine Program, a group operated by the Field Museum, watches the nesting falcons in the city and gathers blood specimens from the young annually. Many of the falcons they observe have ankle bands to distinguish them, which enables scientists to see which falcons are living together.

Along with these observations, the researchers also examined blood specimens from falcon chicks and adults to find out parentage. DNA tests showed just 1 of the 35 broods tested came from “cheating” parents. Even in this case, the scientists suspect a male lost his mate and the coupled with a female who laid eggs that were not his.

“Whenever you have animals living in habitats that have been influenced by human development, you have to wonder how the animals’ life histories will be altered,” Bates said. “It’s important to do studies like this one to see how birds are adapting to living in human environments so that we can monitor changes over time.”

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Image credit: Thinkstock

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