American Kestrel
Sparrow Hawk - Falco sparverius
by Damian Fagan
If you've observed a small raptor perched on a telephone wire or hovering over a sparse patch of highway median, then you’ve probably seen one of the most widespread falcons in North America—the American kestrel (Falco sparverius).
The generic name “falcon” and the genus Falco are derived from the Latin “falcon,” meaning “a hawk.” The name refers to the falcate, or hooked shape, of the bird’s talons. Sparverius has a couple of derivations. One is from the French word “espervier,” which means “sparrow hawk.” The other is from the Latin word for “striped,” a reference to the pattern on the underside of the immature bird's wing.
The American kestrel sports many common nicknames, including, for instance, grasshopper hawk, killy hawk (after its killy, killy, killy call), short-winged hawk, windhover, house hawk, rusty-crowned falcon, and, more commonly, sparrow hawk. Early ornithologists thought these small falcons preferred sparrows as their primary prey and named them the “sparrowhawk.”
While kestrels share some similarities – for example, a hooked bill and sharp talons – with other relatives of the raptor group, they are in fact members of the falcon family (Falconidae), not the hawk family (Accipitridae). Their similarity to the Eurasian kestrel is the source of the “kestrel” name.
Kestrels are the smallest falcons in the Southwest and the smallest diurnal (daytime) raptor in North America. Their larger cousins include the gyrfalcon; the peregrine, prairie and Aplomado falcons; and the Merlin falcon. The gyrfalcon is a boreal species that rarely shows up below the 48th parallel, while the peregrine, prairie and Aplomado occur in the Southwest. The Merlin, like the gyrfalcon, is a northern nester, but will pass through or winter in the Southwest during the non-breeding season.
Kestrels range across much of North America, from Alaska and northern Canada south to Baja and Florida. Their range continues into Mexico and down into South America and east to the West Indies. Though the birds migrate across this range, they may be found throughout the U.S. and southern Canada in winter.
At the Hawkwatch International migration stations in Nevada, Arizona and New Mexico, kestrels are numerous but not the highest numbered migrant. In 2005, 1,468 individuals were recorded in the Goshute Mountains (Nevada); 555, at Yaki Point (Arizona); and 163, in the Sandia Mountains. (New Mexico). Though these birds tend to be short-distance migrants, some travel as far south as Central America.
Kestrels are sexually dimorphic, meaning that there are plumage differences between the sexes. This dimorphism is unique, especially in the case of the juveniles. While many other species of juvenile raptors have first-year plumage that resembles the adult female or is similar between the sexes, the differences between the kestrel sexes are noticeable early in the nestling stage, after the primary feathers have grown about an inch.
As kestrels mature, the males become easily identified by their barred, brick red wings and steel blue backs. The females become distinguished by reddish wings and backs. Another difference between the sexes is that the female’s brick-red tail is barred with thin dark lines and has a shorter black band near the tip of the tail than the male has. The male’s tail feathers are also brick red, but lack the thin horizontal bands. This field character has greater value for identification when the birds are viewed soaring overhead than when they are viewed perching.
Both sexes have dark “eyes,” or ocelli, on the back of their heads. These spots are thought to represent “false eyes,” presumably leading predators to think that the kestrels literally “have eyes in the back of their heads.” (The ocelli may deter attacks from behind, but they don’t guarantee that the kestrels themselves won’t become prey.) The kestrel also bears two dark mustache marks, called malar stripes, that resemble sideburns on either side of the head.
In flight, a kestrel appears skinny and with long, pointed wings. The male has a string of white spots along the back edge of its wings that resembles a string of pearls. These birds can “kite” or “hover” in place, usually when they are searching for prey. Kiting means that the bird can hold steady in the air with the aid of the wind. Hovering means that it can remain in place in the air by beating its wings rapidly.
The ability to hover makes the kestrel a frequent hunter of median strips and highway rights-of-way. It doesn’t need concealment (like the accipiters) or the space (like a peregrine) to run down prey. Unfortunately, the kestrels’ habit of hunting along roadways sometimes makes them susceptible to collisions with passing automobiles.
The hovering makes the kestrels easily identifiable, but the birds can also pull in their wings and zip across the sky. In a soar, those tucked wings spread out to resemble long, tapered candles while the tails appear long and narrow. This makes field identification more tricky.
Though the American kestrel does prey on small birds such as sparrows, those constitute a minor percentage of its diet. In a sense, it is more like an airborne cat. It is an excellent mouser, preying heavily on mice, voles and other small mammals. Grasshoppers, beetles, scorpions, lizards, carrion, smaller birds and amphibians are also counted among its other prey.
Kestrels are birds of open country, but they are cavity nesters. They prefer abandoned woodpecker holes and cracks or narrow holes in cliffs and canyon walls as nest sites. They take readily to nest boxes (artificial structures that contain a small layer of wood pellets and shavings.)
In either a natural cavity or a nest box, kestrels lay an average of four to five whitish or pale pink eggs that are flecked with brown or are occasionally unmarked. The eggs hatch in about a month, and the fledglings leave the nest when they are around 30 to 31 days old. Usually one brood is raised each season, although in years of abundant prey, two clutches may be laid. The female does the majority of the incubating. As the 1 ½ inch-long eggs hatch, the downy young are considered semialtricial, meaning that they are nearly helpless.
The male delivers food for his family to a site near the nest, then calls to the female (kestrels are quite noisy birds in general). She leaves the nest and retrieves the food for the nestlings. The male may cache food to aid in the delivery process once the young are growing and constantly hungry. The parents continue to feed the young for several weeks after they have fledged.
The adult American kestrel averages 12 inches long and has about a two-foot wingspan, but it weighs an average of only three to five ounces. It is truly a quarter pounder with attitude.
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