It’s hard to overstate its prevalence, but DDT didn’t harm peregrines directly. It moved up the food chain from tainted insects to hunted smaller birds and so forth.
“When the birds of prey would eat these other birds, it actually leached the calcium from their bodies,” Katzner said. “So when they would lay an egg, the egg shell would be too thin to support their weight when they were incubating the egg. And so quite literally, no peregrine falcons were hatching and that's why they declined.”
The Environmental Protection Agency banned DDT in 1972.
By the 1980s, at least 20 cities had helped young peregrines nest on skyscrapers. The Denver site was set up in 1988, and it wasn’t long before peregrine falcons thrived in Colorado and around the country. The conservation efforts of Colorado Parks and Wildlife also extended into natural areas, not just highrises.
By 1990, the state counted plenty of the falcons out in the wild and stopped trying to get them to nest downtown.
Katzner noted that the peregrine “was one of the first animals to be added to the Endangered Species Act. And then in 1999, it was one of the first animals to be removed from the Endangered Species Act for the right reasons.”
Many of the cities that introduced peregrines still have them today. You can find web cams trained on them in places like Baltimore, Maryland or at UC Berkeley. The nests are usually active in February through the spring.
“I've heard of people, you know, sitting at a cafe outside in a city, all of a sudden having a pigeon fall into their lap, which I think would be an alarming, uh, lunch activity to have happened,” Katzner said with a laugh. “But, when you are sharing a space with peregrine, you're going to see all sorts of different things.”
Peregrines have been clocked diving at 240 miles per hour, though Katzner said a more typical hunting speed is closer to 40 or 50 miles per hour. They dive on birds mid-air, punching their prey with balled up feet. Katzner said it results in a loud noise and an explosion of feathers.
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Back In The 80s, Denver Gave Peregrine Falcons Swanky Skyscraper Nests. Whatever Happened To Them? - Colorado Public Radio
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