ABOUT AMERICAN KESTRELS

ABOUT AMERICAN KESTRELS

*Please note: there are several species of kestrel, but only the American kestrel occurs in the wild in North America. Any time the word “kestrel” is used alone, please assume it refers to the American kestrel.


American kestrel in flight. All illustrations by Maya Rappaport.

American kestrels are North America’s smallest raptor, or bird of prey. They are considered to be part of the falcon family. Some other members of the falcon family are the merlin, Peregrine falcon, the prairie falcon, and the gyrfalcon. Falcons have sharp, long wings that help them navigate while flying and allow them to make very fast dives. In fact, the fastest bird on Earth is the Peregrine falcon. They can dive at speeds at around 200 mph! That’s about 3 times as fast as a car driving at highway speed.

Recent DNA testing indicates that American kestrels are genetically different than the other members of the falcon family and diverged from a different lineage. Their closest relative, genetically speaking, is the Aplomado falcon, a rainforest dweller of Central and South America. This means that the American kestrel and Aplomado falcon had the same ancestor, which evolved later or differently than the other ancestors of the members of the falcon family.

There are 17 recognized, genetically distinct subspecies of American kestrel. A subspecies is a genetically distinct portion of a species that can look and behave differently from the rest of the species. Genetically distinct mean that the genes of a subspecies - the things that determine things about you and help your body function are genes - are different than the genes of the rest of the population. For example, subspecies of dark-eyed juncos in Massachusetts look different and have a slightly different song from dark-eyed juncos in Flagstaff, AZ. Some subspecies of American kestrel look slightly different from populations here in AZ, and some behave a little differently too.

American kestrels are found in grassland habitats all the way from northern Canada to the very tip of South America.

Kestrels need grasslands to hunt. Like other falcons, they rely on their excellent eyesight and other senses to locate prey. Kestrels eat small animals like insects, rodents, lizards, snakes, and other birds. Depending on the habitat, kestrels can eat more of one thing than another. For example, kestrels that live in habitat with a lot of water might eat amphibians like frogs and toads, while kestrels that live in tall grasslands might eat more things like grasshoppers and mice. They need open grasslands to hunt in. Kestrels fly over grasslands, or perch over them on trees or electrical wires, and then quickly dive to capture prey. Something that makes kestrels unique is their ability to hover in place while flying. Only a few other bird species (like hummingbirds) can hover. This helps kestrels to find and catch prey.

Kestrels are secondary cavity nesters. This means that they raise their babies in holes that have been created by other animals like woodpeckers. Kestrels aren’t able to dig out a nesting cavity themselves, and require existing holes in trees, cliffs, and human structures. We can help support kestrel populations by building nesting boxes for them to provide more cavities, which are a limited resource in many habitats. Recent fire management plans in many areas prioritize removing snags, which is a word for standing dead trees. Snags, because they are often soft and easy to excavate, and sometimes hollow, make excellent nesting cavities for many species, including birds, insects, spiders, and mammals like raccoons. In areas where many snags have been removed for hiker safety or to help prevent forest fires, installing nesting boxes may help kestrels by creating more places where they can raise their babies.

American kestrels lay clutches of 2-6 eggs, often laying 4-5 eggs. In rare cases, they can “double clutch”, meaning they can incubate, hatch, and raise two groups of babies in a single season. If their nest fails (because of a predator attack, weather event, or other factors), they will often nest a second time. Kestrel eggs take about 30 days to hatch, and kestrel chicks take about 30 days to leave the nest, or “fledge.” After fledging, kestrel chicks rely on their parents for food for about 2-3 weeks. In mid to late summer, it is common to see a group of several kestrel fledgelings together, as they will often stay close to their siblings until they get a good handle on skills like hunting and flying.

AMERICAN KESTREL IDENTIFICATION:

Male American kestrel on a nest box.

American kestrels are small falcons. They are sexually dimorphic, meaning that female kestrels look different from male kestrels. The differences between females and males are visible in American kestrels as young as 3 weeks old.

American kestrels are small birds, appearing to be about the same size as American robins, mourning doves, or blue, Steller’s, or pinyon jays. They have a wingspan of approximately 22 inches, and are approximately 8-11 inches in length. Like most raptors, females are larger and heavier than males, though this difference can be hard to see.

Kestrels can appear larger or smaller depending on if their feathers are fluffed up. Birds fluff up their feathers for many reasons, including when they are cold, sick, or feeling threatened. Some birds fluff up their feathers to communicate other kinds of information with one another.

Both sexes of American kestrel have reddish, barred backs with dark, vertical facial markings. Some people call these markings a “double moustache.” Male kestrels have slate blue wings. Female kestrels have reddish, barred wings. Both female and male kestrels have slate bluish coloring around the crowns of their heads, but male kestrels have a notable bright reddish-orange cap. The female’s orange cap is somewhat duller in color, smaller, and harder to notice.

Female American kestrel on a cattail.

American kestrels often flick their tails while perched. This can help you identify them if you happen to see them in the field! I always look for kestrels when I’m around open grasslands. I look over the grassland for hovering kestrels, and check any perches - wires, branches, trees, posts, signs, etc. - for perched kestrels.

KESTRELS AND OUR COMMUNITY:

American kestrels are an important component of the ecological tapestry that interconnects all life: insects, fungi, plants, mammals, birds, bacteria, humans, and more. No one component has a “purpose” in the human sense of the word, but all components of the natural world are important and serve functions for other parts of a habitat system.

Here in Northern Arizona, grasslands are an important part of our habitat, interlinking Ponderosa pine forests, wetlands, canyonlands, stream-side (or riparian) habitats, and human settlements. Grasslands, with the many hiding places and food sources they provide, nourish many kinds of life, including wildflowers and native grasses, insects, rodents, snakes, lizards, amphibians, grassland bird species, wild ungulates like deer and elk, and more. From the human perspective, grasslands provide a place to graze cows and sheep. They are also excellent places to watch wildlife and enjoy the natural world. Grasslands, with their large diversity and volume of life, produce fertile topsoil. Their variety of plants help prevent erosion, and they filter and clean water.

Kestrels, as grassland obligates (meaning, they must have grassland habitat to thrive), serve many functions in their habitat system. They are food for other birds of prey including Cooper’s hawks. And because they are voracious predators, kestrels control populations of insects, rodents, birds, etc. Farmers that struggle with agricultural “pests” benefit from kestrels on their lands. Recent research shows that kestrel nestboxes may deter bird species from taking up residence in orchards. And they may help farmers use less pesticides as well.

Compiled by Maya Rappaport, Flagstaff Kestrel Project Coordinator. August 2019.

Works Cited

American Kestrel Identification, All About Birds. Cornell Lab of Ornithology. (n.d.). Retrieved from https://www.allaboutbirds.org/guide/American_Kestrel/id
American kestrels, most common predatory birds in U.S., can reduce need for pesticide use. National Science Foundation. (n.d.). Retrieved from https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=244549
Kestrel biology overview: American Kestrel Partnership. The Peregrine Fund. (n.d.). Retrieved from https://kestrel.peregrinefund.org/kestrel-biology
Research Reveals Exactly Why Peregrine Falcons Are so Deadly. Audubon Society. (2018, April 13). Retrieved from https://www.audubon.org/news/research-reveals-exactly-why-peregrine-falcons-are-so-deadly
What is an American kestrel? Hawk Mountain Observatory. (n.d.). Retrieved from https://www.hawkmountain.org/raptorpedia/hawks-at-hawk-mountain/hawk-species-at-hawk-mountain/american-kestrel/page.aspx?id=498