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NATURE HAPPENINGS - August 2006


The Falcon of the Sparrows
by Damian Fagan

The smallest North American falcon, the American kestrel, bears the cross of mistaken identity. The scientific name Falco sparverius is, at least, somewhat correct. Falco is a Latin word meaning “hooked” or “falcate” which describes the shape of the claws. Sharp and shaped like a scythe, the claws are used for grasping prey. Sparverius is derived from the Old French espervier meaning “falcon of the sparrows.” Older field guides boldly pronounce this species as the “sparrow hawk.” This is where the confusion arises because the kestrel is not a hawk and small birds comprise only a small percentage of their diet.
Though American kestrels do take small birds, like sparrows, their diet consists more of insects, small mammals and reptiles. I guess “insect hawk” or “reptile hawk” just didn’t sound right. Plus the kestrels other relatives — the merlin, peregrine and prairie falcon — are proficient hunters of birds. Perhaps the early naturalists assumed that the kestrel would follow in the wingbeats of the other members of the Falco genus.

Ornithologists borrowed the name “kestrel” from the Eurasian kestrel, which our species resembles. If you look up kestrel in Webster’s dictionary, he defines it as echoic or an imitation of the Old French word cresserelle.

Europe aside, kestrels are the most colorful birds of prey in North America. Males and females wear different plumages, although both have dark vertical sideburns (often called mustache marks), reddish-brown backs and pointed wings. The adult males differ in that their wings are steel blue, the reddish tail has a large dark band near the tip, and the breast is rufous with dark spotting on the belly. The adult females who are a bit larger than the males, sport dark barring on their tail, brownish streaking on their breasts and bellies, and have a small dark band near the tip of their tail.

One feature both sexes share is a pair of dark spots called ocelli on the back of their nape. These “false eyes” are thought to be deterrents for predators. The predators mistake the spots for watchful eyes and try for some other prey. Probably a good feature to have for a bird that spends a great deal of its time looking down, but kestrels still fall prey to other raptors.
Predators themselves, kestrels hunt mainly by the perch-and-pounce method. They sit motionless on a fence post, tree limb, telephone wire, or rocky outcrop and watch for movement below. From their location they drop down on prey such as grasshoppers, beetles, mice, voles, ground squirrels, lizards, the occasional frog or toad, and snakes.

Another hunting behavior is by hovering over an open field and then descending upon their prey. This type of behavior is unique to the kestrels, so it is thought to be more common than it really is.

Like their larger relatives the prairie or peregrine falcon, kestrels are birds of open country. Don’t expect to find them in deep woods; these are birds along the woodland edge or in the open field. There have been some noted declines in populations in the northeast and Canada, but some researchers believe that reforestation may play a role in limiting the kestrel’s preferred habitat.

Kestrels occur in grasslands, shrub-dotted landscapes, city parks, agricultural fields, rocky canyons, and open woodlands. They need cavities in which to nest, so they utilize abandoned woodpecker holes, crevices or cracks in cliff walls or buildings, or nest boxes to lay their eggs in.

Other than some small owls, like the screech owl or boreal owl, kestrels are the only diurnal raptor to use artificial nest cavities. You would think that there are enough woodpecker holes or cracked buildings to go around, but kestrels take to nest boxes like ducks to a pond.

Most nest boxes are made of rough cut cedar, but any untreated wood would work. The boxes generally are 8-10 inches tall and 7-8 inches wide. The entrance hole is 2.5-3 inches wide and circular. A good placement for a box is where the entrance hole is about 15-20 feet up from the ground, faces the southeast and is generally unobstructed. Since kestrels don’t add nesting material to the box, a 2-3 inch layer of wood shavings with some wood pellets is added. Located near some perches, the kestrels will take up residency.

Sometimes nest boxes are mounted on power poles or highway signs. On your next trip to Grand Junction, check the westbound signs along I-70 in Colorado for these boxes. Though the highway traffic is a hazard the kestrels must contend with, often the median strips represent a smorgasbord of insects and small mammals.

Around Moab, kestrels are fairly common. In the fall, migrants move southward from their northern breeding grounds. Attentive birders may notice numerous birds perched along telephone lines or hovering over the edge of an agricultural field. If you’re able to watch the hunting antics of these small falcons, you might get a sense of some of their other names like “house hawk, killy hawk or windhover.” Monikers like those makes “falcons of the sparrows” seem like an OK name after all.

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