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What’s Happening to the American Kestrel?

In North America, the population of the American kestrel has declined by nearly 50% since the 1960s.  

“We still don’t know what threat, or threats, have ultimately pushed the American kestrel to the point of failing to maintain populations across the continent,” says Jacque Williamson, the curator of education & conservation at The Brandywine Zoo in Wilmington, Delaware.  

I spoke with Williamson, who has been studying kestrels in Delaware since 2014, during a recent visit to the zoo. The American kestrel, Williamson explained, is one of the smallest species of falcons in North America.

“Kestrels have gone locally extinct in a number of places in North America,” Williamson said. “We’re doing our best to understand the reasons, stop this trend, and potentially reverse it.”  

American kestrels are “cavity nesters,” which means they nest in unoccupied holes in trees and buildings, for example. With help from the Delaware Kestrel Partnership, the Brandywine Zoo has put up boxes around the state to provide a spot in which the birds can nest.

“Kestrels are picky about where and which boxes they want to use,” Williamson said. “We, as researchers, have to guess which locations are the best spots to put a nest box and hope that kestrels agree.” 

When a kestrel nests in one of the boxes, researchers put a numbered leg band on the bird so that the next time it is found, its origin will be known. If researchers keep catching the same kestrels year after year, they will be able to determine how old the birds are and how well they are doing.

Unfortunately, the return rate of the leg bands is less than 3%. As is the case across North America, the birds are suffering. But so far, the reason remains a mystery.

One possibility is a loss of habitat (grasslands and open farmland) to development. Pesticide accumulation could be another culprit since the toxins may hurt both the kestrels and their prey. Other contributing factors could be new zoonotic diseases (which are caused by the transmission of germs between people and animals), competition with invasive species for nest boxes, or climate change. 


Sophia visited Delaware’s Brandywine Zoo, where she spoke with an expert about the mysterious decline of the American kestrel. 


In North America, the population of kestrels has declined by nearly 50% since the 1960s. In the mid-Atlantic region, where Delaware is located, their population has suffered even more, declining by 88% since the 1970s, according to a government survey.

You can help the American kestrel by teaching people about the bird and adopting bird-friendly practices to help all wildlife. For example, keep your pet cat indoors, download nature apps to share what wildlife is in your backyard, and buy bird-friendly products. This means avoiding toxins that are designed to kill rodents. To help birds see your windows so that they avoid flying into them, draw the blinds, move houseplants away, and soap windows. 

Another important thing you can do is plant native species. Invasive plant species crowd out native species, which is bad for the ecosystem. Native wildlife need native plants to eat and use as protection.

Jeff Downing, the executive director of the Mount Cuba Center, a public garden outside of Wilmington, Delaware, recently explained the many rewards of planting native species. “By adding a native plant or tree here or there,” he told a local reporter, “you will feed more wildlife and have the benefit of seeing more native butterflies, caterpillars, and birds in your backyard.”


Photos courtesy of the author