Western Great Lakes Bird and Bat Observatory

Citizen Science


By Kate Redmond

Shakespeare asked, “What’s in a name?” Because of their size and the fact that they will prey on small birds, older field guides call American Kestrels (Falco sparverius) Sparrow hawks, which is what its species name, “sparverius,” means. Like the Eurasian Kestrel, a rare visitor to North America, the American Kestrel is a falcon, but the Eurasian Sparrow hawk is in a different raptor family, the Accipiters.

American Kestrels have a huge range -- they are permanent residents across much of the United States, northern Mexico, and a pretty big chunk of South America (here’s their eBird footprint http://ebird.org/ebird/map/amekes), and they breed, but don’t overwinter, across the northern Great Plains and Rockies and in Canada well into the Arctic Circle. These remarkably adaptable birds are found in scrublands, grasslands, and agricultural areas and on woody edges from sea level to elevations of 14,000 feet, wherever there is hunting and nesting habitat. They are a common sight perched on telephone wires during Wisconsin winters -- often with a small rodent dangling from their talons.

Kestrels, our smallest falcons, are about nine to eleven inches long with wingspans close to two feet -- they’re roughly the size of Mourning Doves and are often mistaken for them. Kestrels are sexually dimorphic (“two forms”); males are more colorful than females, and females are about 10% larger than males. https://www.birdwatchingdaily.com/blog/2015/04/17/armchair-birding-compare-male-and-female-american-kestrels/. Both have a rust-colored back and a pair of dark markings called moustache marks on each side of their face. Two black spots on the back of the neck are thought to mimic eyes and may startle predators attacking from the rear. They are often heard before they’re seen; their most common call is series of loud klee-klee-klee or killy-killy-killy notes https://www.allaboutbirds.org/guide/American_Kestrel/sounds.

Their flight is swift, and their silhouette is described as “anchor-like.” Because they have less muscle mass, they are not as “bulky” as the larger Merlin and Peregrine falcons and so can survive with proportionately less food. They may grab insects out of the air, but they typically hunt from perches or while hovering, ambushing their prey rather than chasing it.

A kestrel’s diet changes with the seasons. Insects, especially dragonflies and large grasshoppers, provide the bulk of their food in warmer months, and they also catch beetles, caterpillars, earthworms, crayfish, frogs, bats, mice, and songbirds (and they’ve been seen taking birds as large as a flicker). Rodents, chiefly voles (Microtus), make up the bulk of their winter diet in Wisconsin. Kestrels generally eat smaller prey on the ground and carry their larger prey to a perch, and they will cache surplus food for later use, especially in winter. They sometimes hunt in family groups. They are preyed on by larger raptors like Red-tailed, Cooper’s and Sharp-shinned Hawks, and by crows, raccoons, skunks, and rat snakes.

Voles mark their comings and goings with scented urine, and researchers have found that these trails reflect ultraviolet light. Many references say that kestrels can spot these trails from above, allowing them to determine whether an area will be a productive hunting ground. Other researchers say that although gulls, shorebirds, Passerines (the perching/songbirds), and a few other groups of birds do have UV vision, raptors are not very sensitive to UV light and do not use it to find prey.

Unusual among hawks and falcons, kestrels are cavity nesters that use old woodpecker holes, natural hollows in trees, and even crevices in rock piles, as well as man-made nest boxes, and they will kick out any bird or squirrel that may already be in residence. They can be fairly tolerant of human neighbors -- I once saw a kestrel fly into a hole under the eaves of a building in the middle of a small town. Trees at the edge of a woodland are ideal sites.

Males defend territories during the nesting season and will chase raptors much larger than they are. He courts with aerial displays, flying into the sky and then plunging in a steep dive while vocalizing. The female responds by flying with slow, stiff, dove-like wingbeats, and the pair may exchange gifts of food, on the wing.

The male searches for potential nest sites and then takes the female around and shows them to her, but she makes the final choice. Inside the cavity, the nest is primitive -- often just a scrape on the floor. Both parents incubate the eggs, though the female pulls the lion’s share of the duty. The young fledge after about a month, but the parents continue to feed them for a few more weeks, and after that, young birds may congregate with young from other nests.

Southern populations don’t necessarily migrate, but northern-breeding kestrels do, leap-frogging over resident populations to overwinter in the southern United States and in Central America. They are solitary in winter -- females head south first and claim territories in open areas on their wintering grounds, leaving the later-arriving males with the less-choice habitats. Males fly north first.

Kestrels have, as the TV stations like to say, “A Wisconsin Connection.” Wisconsin biologist Fran Hammerstrom, who studied Greater Prairie-Chickens for decades, decided to try to encourage kestrel nesting on the Buena Vista Grasslands by erecting 40 nest boxes in 1968. That project morphed into the Central Wisconsin Kestrel Research project, which she headed for the next 30 years, until her death. The project continues today.

It’s hard to imagine that populations of a bird that is so abundant and adaptable and that enjoys such a broad menu might be shrinking, but kestrel numbers on the East and West coasts are in decline. Data from the North American Breeding Bird Survey show an over-all drop in numbers of almost 50% from 1966 to 2010. The main challenge is the loss of nesting and hunting habitat due to urbanization, reforestation, and “clean” agricultural practices that remove dead trees and hedgerows. The use of pesticides that kill the rodents and insects that they depend on, deliberate killing, predation by Cooper’s Hawks, competition with starlings for nest boxes, and collisions with cars and with wind and communication towers also take their toll.

The National Audubon Society considers kestrels “climate threatened” http://www.audubon.org/field-guide/bird/american-kestrel, but others suggest that the falcons may benefit from climate change because it could make prey more available, cause the birds to nest earlier, giving them first crack at good nest sites and territories, and allow the young of the year to get more experience and conditioning before they migrate. What can you do for kestrels?

LINKS BBS and CBC maps   https://www.mbr-pwrc.usgs.gov/infocenter/i3600id.html

GOOD WEB SITE: http://www.hawkmountain.org/raptorpedia/hawks-at-hawk-mountain/hawk-species-at-hawk-mountain/american-kestrel/page.aspx?id=498

Calls - https://www.allaboutbirds.org/guide/American_Kestrel/sounds

http://www.audubon.org/field-guide/bird/american-kestrel To find out more and get involved with Central Wisconsin Kestrel Research, please visit the program’s website at: http://www.kestrelresearch.com