American kestrels are found in a wide variety of habitats, including
grasslands,
meadows,
deserts and other open to semi-open regions. They can also be found in both urban and suburban areas. A kestrel's habitat must include perches, open space for hunting, and cavities for nesting (whether natural or man-made). The American kestrel is able to live in very diverse conditions, ranging from above the Arctic Circle, to the tropics of Central America, to elevations of over in the
Andes Mountains. The bird is distributed from northern Canada and Alaska to the southernmost tip of South America,
Tierra del Fuego. It is the only kestrel found in the Americas, though as mentioned above this classification is genetically inaccurate. It has occurred as a vagrant in the UK, Denmark, Malta and the
Azores. File:American Kestrel on the hunt.jpg|Female about to pounce File:20210506-DSC 3800.jpg|alt=Male showing female a nest box and offering mouse – Maine|Male showing female a nest box and offering mouse – Maine File:20200704-DSC 1454.jpg|alt=Female feeding nestling – Maine|Female feeding nestling – Maine File:20200707-DSC 1815.jpg|alt=Just fledged male|Just fledged male – Maine American kestrels in Canada and the
northern United States typically migrate south in the winter, some of them converging with resident kestrels of smaller size in Mexico, sometimes going as far as Central America and the Caribbean. Birds that breed south of about 35° north latitude are usually year-round residents. Migration also depends on local weather conditions. American Kestrels breeding at lower latitudes – below 48ºN to be precise – arrive earlier after warmer springs, whereas birds from higher latitudes return to their breeding grounds at the same time each year. These patterns suggest that short-distance migrants are better able to cope with climate change. Wintering kestrels' choice of habitat varies by sex. Females are found in open areas more often than males during the non-breeding season. A common explanation for this behavior is that the larger females who are bigger than the males arrive at the preferred habitat first and exclude males from their territory. The American kestrel is not long-lived, with a lifespan of <5 years for wild birds. The oldest
banded wild bird was 11 years and 7 months, while captive kestrels can live up to 14–17 years.
Feeding American kestrels feed largely on small animals such as
grasshoppers,
crickets,
butterflies,
moths,
dragonflies,
beetles,
lizards,
mice,
voles,
shrews,
frogs,
bats, and
squirrels. The kestrel is able to maintain high population densities, at least in part because of the broad scope of its diet. The American kestrel's primary mode of hunting is by perching and waiting for prey to come near. The bird is characteristically seen along roadsides or fields perched on objects such as trees,
overhead power lines, or fence posts. It also hunts by kiting, hovering in the air with rapid wing beats and scanning the ground for prey. Other hunting techniques include low flight over fields, or chasing insects and birds in the air. Prey is most often caught on the ground, though occasionally they take birds in flight. Before striking, the kestrel characteristically bobs its head and tail, then makes a direct flight toward the prey to grab it in its
talons. Much like the
red-tailed hawk, American kestrels conserve energy in a hunt and pick their attacks with care as to position and odds of success.
Reproduction American kestrels are sexually mature by their first spring. In migratory populations, the males arrive at the breeding ground before females, then the female selects a mate. Pair bonds are strong, often permanent. Pairs usually use previous nesting sites in consecutive years. This gives birds an advantage over younger or invading individuals, as they would already be familiar with the hunting grounds, neighbors, predators, and other features of the site. Males perform elaborate dive displays to advertise their territory and attract a mate. These displays consist of several climbs and dives, with three or four "klee" calls at their peaks. Females are promiscuous for about one to two weeks after their arrival at the nesting site. This is thought to stimulate
ovulation. Food transfers from the male to the female occur from about four to five weeks prior to egg laying to one to two weeks after. American kestrels are cavity nesters, but they are able to adapt to a wide variety of nesting situations. They generally prefer natural cavities (such as in trees) with closed tops and tight-fitting entrances that provide for maximum protection of the eggs and young. Kestrels occasionally nest in holes created by large
woodpeckers, or use the abandoned nests of other birds, such as
red-tailed hawks,
merlins, and
crows. They have been recorded nesting on cliff ledges and building tops, as well as in abandoned cavities in
cactuses. Three to seven eggs (typically four or five) are laid approximately 24–72 hours apart. (Two supernormal clutches of eight eggs and one of nine have been documented. One egg in one of the eight-egg clutches hatched as did one egg in the nine-egg clutch.) The average egg size is , 10% larger than average for birds of its body size. The eggs are white to cream in color with brown or grey splotching. Incubation usually lasts 30 days and is mainly the responsibility of the female, although the male incubates 15–20% of the time. Eggs that are lost are typically replaced in 11–12 days. Hatching takes place over three to four days. Hatchlings are
altricial, and are only able to sit up after five days. They grow rapidly, reaching an adult weight after 16–17 days. After 28–31 days, their wings have developed and they are able to leave the nest. The young adult kestrels may breed from a year old, and the species has approximately a three to five-year life expectancy in the wild. In ecological terms, the reproductive pattern of the American kestrel leans towards a small bird "
r selection" strategy. In
r/K selection theory, selective pressures are
hypothesized to drive
evolution in one of two generalized directions:
r or
K selection.
R-selected species are those that place an emphasis on a high growth rate, typically exploiting less-crowded
ecological niches, and produce many
offspring, each of which has a relatively low probability of surviving to adulthood (i.e., high
r, low
K). By contrast,
K-selected species display traits associated with living at densities close to
carrying capacity, and typically are strong competitors in such crowded niches that
invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood (i.e., low
r, high
K). Between these two extremes, the American kestrel is one of the few raptor species that lean towards being
r-selected. They are able to breed at one year old, have few non-breeding adults in the population, and have larger broods. Their population growth rate is high relative to larger raptors, which typically lean towards being
K-selected. This said, older American kestrel pairs generally have larger brood sizes and produce more viable offspring than younger conspecifics. ==Stress physiology==