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Establishing a Nest Box Program for American Kestrels Along an Interstate Highway

The American Kestrel: North America's Smallest Falcon


The American Kestrel (Falco sparverius), formerly known as the Sparrow Hawk, is about the size of a Blue Jay. Both sexes have rusty-colored tails and backs with black barring. The wings of the female also have the rust and black color pattern, while the wings of the male are blue-gray.
Range and Habitat:
American Kestrels live in North, Central and South America from the tree line boundary in Alaska and Canada south to Tierra del Fuego. Kestrels prefer open country, and will inhabit unforested mountainsides up to 1300 feet, grasslands, savannas, deserts, farmlands, and even suburban and urban environments.

Migration:

Those in the northern parts of the breeding range migrate, while other populations are less migratory. Populations south of approximately 35°N (same latitude as Memphis,Tenn.) are, for the most part, permanent residents.

Kestrel movements are not well understood, but information from the recovery of banded birds indicates the northernmost kestrels winter the farthest south (Central America to Panama). Iowa's kestrel population probably contains a mixture of birds that nest in Iowa but winter to the south, birds that winter in Iowa but nest farther north, and those that are year-round residents.

JPG - American Kestrel
American Kestrel

Food Habits:

American Kestrels are generalist predators, feeding on large insects such as grasshoppers, small mammals such as voles, birds of sparrow size, and in some places, reptiles and amphibians.

Pairing:

American Kestrels are monogamous. Pairing begins approximately four weeks prior to egg laying. The male establishes a nesting territory and is joined later by the female, who may move among several territorial males before choosing a mate. The male, or sometimes the female, will try to attract a potential mate's attention by exhibiting a series of power dives from high above the territory. Pairs form and courtship feeding, where the male presents food to the female, becomes frequent. Copulation may precede egg laying by several weeks and occurs with diminishing frequency as egg laying approaches.

Nest Site Selection:

Both sexes have been observed searching for suitable nest sites. American Kestrels are almost exclusively cavity nesters and will use a natural hole in a tree, a woodpecker's hole, a nest box, a cavity in a bank or cliff, or an enclosed space in a building. On rare occasions, kestrels may use an old stick nest of another bird, especially the enclosed nests of magpies.

JPG - Nesting Kestrel
American Kestrel incubating eggs in a nest box.

Eggs:

Eggs are white to reddish-brown, usually with reddish-brown spots. Generally, four to five eggs are laid at one- to two-day intervals.

Incubation:

Incubation generally begins with the second to the last egg laid, and lasts 29 to 30 days. The female does most of the incubation, with the male providing her with food. He occasionally assists with incubation.

Nestling Period:

Kestrel young are tended by both parents. The female broods and feeds the new nestlings, and the male brings all the food. The nestlings are downy white at first, but become well feathered by 20 days of age. The young develop rapidly, leaving the nest 28 to 30 days after hatching.

Post-fledgling Period:

After nest departure, the young are dependent on their parents for food for two to three weeks.

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