American kestrels are tiny, colorful and feisty. Attitude-wise, they’re the chihuahuas of the avian world: They’re unafraid to take on much larger birds, ready to backstab turkey vultures and dive-bomb golden eagles to defend their territory.
But despite being the United States’ most abundant falcon, American kestrels are struggling. In response to their decline, scientists have set up nest boxes to provide more habitat for these Lilliputian predators. Just how much these efforts are helping remains to be seen.
Not much bigger than a robin, American kestrels are the smallest falcons in North America. Males are slightly smaller than females, plus they sport streaks of slate blue on their wings that contrast stylishly with the rest of their rust-colored plumage. Such disparities in appearance between males and females in the animal kingdom are called sexual dimorphism. The black facial markings, present on both sexes, are commonly called sideburns and mustaches.
American kestrels are found throughout the Americas, from Canada to Argentina’s southern tip. Come fall, kestrels from Canada and Alaska head south in search of food, returning north in the spring to breed, while birds in warm locales like Southern California can stay put year-round.
Aerial acrobatics are the kestrel’s forte. In particular, kestrels are fantastic hoverers: The birds can stay suspended by flying into a headwind or by beating their wings furiously, like a hummingbird.
This ability helps them ambush prey, allowing them to swoop down on their targets. Kestrels can also snatch their quarry in mid-flight. Nimble and light, they are the dogfighters of the raptor world, unlike hawks and eagles, which tend to cruise through the air.
The kestrel’s diet is diverse, consisting of insects, rodents, small reptiles and occasionally smaller birds. Kestrels are not afraid to go after animals that are bigger than they are; researchers have even observed them feeding kingsnakes to their young.
Prime kestrel habitat consists of meadows and farmland dotted with trees and snags. In and around active nest cavities, researchers often find multivitamin-shaped pellets of undigested food such as animal bones, reptile scales and insect parts.
Across North America, kestrel numbers have fallen by half since the 1960s. The decline has been even more precipitous in coastal California and the Southern Rockies. Though the reasons aren’t fully understood, scientists suspect that habitat loss from development, dwindling food sources and competition for nesting sites from invasive species, particularly starlings, are among the contributing factors. A 2018 study found that on average, kestrels are shrinking in size, indicating that many are chronically undernourished.
One thing seems to be giving kestrels a boost: nest boxes. Over a thousand have been set up across the U.S., and at some sites, roughly two-thirds of them have become breeding homes for kestrel couples. Some have hosted kestrel families for decades.
Around California’s Mount Diablo, which boasts warm weather and abundant grass-covered hillslopes, a nest-box program has entered its eighth season. Several boxes have fledged up to five chicks for several consecutive years. Cameras installed at these boxes help scientists monitor the local population and understand the forces behind shifting kestrel numbers.
Illustrations by Shi En Kim.
This story is part of High Country News’ Conservation Beyond Boundaries project, which is supported by the BAND Foundation.
This article appeared in the August 2025 print edition of the magazine with the headline “Get to know the American kestrel.”
