Life Science

Peregrines move in upstairs

These powerful raptors have claimed urban areas, but their populations could still be at risk

June 18, 2015
This peregrine dives to catch its prey, reaching speeds above 200 miles per hour. [Image credit: Flickr user Nic Trott]

The soft peeping of the four baby peregrine falcons was a dainty counterpoint to the grinding of the oil refinery’s machinery. Grime and grit, by-products of the refinery, coated the narrow ledge where the babies huddled in their nest, guarded by their protective mother. Armed with razor talons and a hooked beak, the mother stared down Kathy Clark, who was balanced in a bucket lift and trying to reach past her to attach leg bands to the chicks.

Normally, the bird would have dived at Clark, dashing her with her beak and talons, but this nest was tucked back in a crevice and she didn’t have the room to maneuver.

“When they can’t fly at you, they don’t quite know what to do,” said Clark, remembering the spring day, last year. “But they really hate you.”

Clark is a biologist at the New Jersey Division of Fish and Wildlife, and has been working on peregrine falcon conservation for two decades. She says she tried to scare this protective mother away from its nest so she could finish the banding, which allows scientists to track the falcons over the course of their 16-year life.

If not for the dedicated and occasionally crazy work of conservationists like Clark, peregrine falcons might have gone extinct in North America 50 years ago. Now, with a stable, even urban, population, the peregrine’s story is widely regarded as one of the most successful conservation projects ever. But some biologists worry that the fight for the peregrine is far from over, even though the birds have found success in man-made environments.

Peregrines are resourceful pioneers and are colonizing urban spaces like bridges, skyscrapers and industrial spaces like oil refineries. One pair even made its nest in a flowerpot on a condo balcony in Wildwood Crest, New Jersey.

But decades ago, peregrine falcons were a rare sight even in their natural habitat. The peregrine falcon population crashed in the 1950s and 1960s, most likely due to the pesticide DDT, which made their eggshells so fragile that they would break before the chicks were ready to hatch. If the mother had been exposed to too much DDT, the chemical could even poison the embryo outright. The U.S. Fish and Wildlife Service states that by 1975 only 324 known nesting pairs were left in the United States, less than a tenth of their numbers in the 1940s.

“It was a dicey time,” Clark said. If the population numbers had dipped too low, it may have been too hard for birds to find mates and genetic diseases caused by inbreeding would have begun to crop up. Since it was the reproductive process that was being affected, the population would crash even faster because there would be no young to carry on the fight.

According to the Peregrine Fund, a conservation organization that was essential to the rehabilitation effort, there was not a single known nest east of the Mississippi by 1965. The organization started the mission to save its namesake in 1970 and now there are around 2,000 nesting pairs.

“We could stop all active management tomorrow, and they would probably be fine,” said Marcel Gahbauer, a conservation biologist at the Migration Research Foundation in Quebec, Canada, who investigated the stability of the peregrine falcon population in northeastern North America. In a study published in the Journal of Wildlife Management in January, he found that survival rates of peregrine chicks in more natural, rural environments were surprisingly similar to those of their urban counterparts. Both urban and rural chicks were making it to adulthood at promising rates, and there were enough of them that conservationists now aren’t as worried about the population.

Their success is partly due to the fact that researchers at the Peregrine Fund, located at Cornell University at the time, were willing to try anything. One male falcon could produce enough semen to inseminate several females a day; the trick was getting it to produce the sample. Since some of the males had accidentally grown up believing they could mate with humans, handlers would wear a special rubber hat when interacting with the birds. The falcons would mate with the hat, depositing sperm into it that the researchers could use to inseminate females.

Wild peregrine parents sometimes fostered chicks, but the Peregrine Fund also refined a technique called hacking, in which they raised captive chicks without parents. Using special food doors and open cages Clark said, they provided a pseudo-natural environment where the birds could grow up with fewer risks but still gain the skills they would need to live in the wild.

Eventually, the Peregrine Fund began releasing birds into the wild. They worked with organizations across the country, releasing over 6,000 birds by the mid 1990s, according to the World Working Group on Birds of Prey and Owls, another conservation organization.

When some falcons began using the high ledges of skyscrapers and bridges as additional nest sites, conservationists were eager to help the urban raptors adapt to prime real estate by providing more secure nests.

“These birds nest in mid to late march and there can be nasty storms and cold rains,” Gahbauer said. Nest boxes, man-made structures that are carefully placed in ideal nesting spots, provide cover from the elements and boost chick survival. Nest trays are also used sometimes, which have a sturdy base and a raised lip to help prevent chicks from falling out of the nest, but Gahbauer said it is “having that overhead shelter that made the biggest difference.”

Not every bit of urban peregrine news is so happy, however. There is some evidence that a new suite of chemicals is beginning to accumulate in urban peregrines: flame retardants. These chemicals are found in many consumer products, from electronics to furniture and building materials. They leach into the environment during manufacturing or disposal, and are picked up by the birds that peregrines eat. Adult peregrines are the top of their food web, so they end up consolidating chemicals from all of the prey they eat, increasing their exposure.

Scientists can measure the amount of a chemical in an adult by analyzing unhatched eggs, because compounds in the mother are passed into the eggshell. “The levels we’ve found in peregrine falcons are the highest we’ve ever found in threshold animals,” said Da Chen, an ecologist at Southern Illinois University who researches contaminants on wildlife, including peregrines. The effects of flame retardants on peregrine falcon health and reproduction are still being studied. Chen says he doesn’t predict these chemicals are currently as direct a threat to peregrines as DDT was, but “it’s always a risk.”

Gahbauer wonders to what extent it’s a brewing problem, pointing to how quickly the population crashed in the 1960s. “It has to be tough with the chemical soup out there to say something is the factor, but I think there are reasons for concern.” For now, no one is calling for a ban on flame retardants, but scientists are unsure how urban environments can ultimately affect these falcons. Moving into areas with a higher concentration of industrial chemicals might harm the birds to some extent, but the benefit of extra territory and nest sites in our cities might balance out the risk.

Work on understanding the bird and its environment will continue while the species colonizes the urban frontier. Although the rehabilitation of the peregrine falcon is a success story, our new avian neighbors may someday need our help again. “In the event something else comes along,” Gahbauer said, “it would be helpful to have the tools in hand to maximize their success.”

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