The American Kestrel, Falco sparvenius, formerly called Sparrowhawk because sparrows were believed to be a dietary preference, is classified as a species of least concern. This bird is the smallest and most colorful of North American falcons. Males are more brightly colored than females, although females are larger than males. Because of their appetite for small rodents such as mice and squirrels, these small falcons play an significant role in predation of a variety of rodent species. They are the only North American falcon that regularly hunts by hovering or kiting (sailing on the wind).
The species is found broadly across North and South America. The breeding range extends from central and western Alaska eastward through northern Canada as far as Nova Scotia south of the Arctic tree line. Southward the range flows to central Mexico and to the Caribbean Basin. F. sparvenius is a local breeder in Mesoamerica. The species is not regularly found in the high mountains or in temperate and tropical rainforests.
Habitat and ecology
Preferring to hunt in open areas, this species can be found in open fields, farmlands, pastures, marshlands, grasslands, savannas, canyons, borders of woodlands, deserts, and suburban areas with high, exposed perches such as trees, utility poles and even giant cacti.
Falco sparvenius is often preyed upon by certain larger raptors, including Red-tailed Hawk, Buteo jamaicensis, Northern Goshawk, Accipiter gentilis, Coopers Hawk, Accipiter cooperii, and falcons such as Peregrine Falcon, Falco peregrinus, and a number of owls, including Barn Owl, Tyto alba, and the Great Horned Owl, Bubo virginianus.
The American Kestrels is a small falcon, with the male generally smaller than female. Males are 22-26 cm (8-10 in) long with a wingspan of 52-57 cm (20-22 in) and weigh 97-120 gm (3.4-4.5 oz). Females are 23-27 cm (9-11 in) in length, 54-61 cm (21-2 in) in wingspan and weigh 102-150 gm (3.6-5.3 oz) .This bird exhibits a short, dark, hooked beak, rounded head, long tail, and long narrow pointed wings. The top (crown) of the head, is gray and the species manifests white cheeks, blue-gray wings, and “eye spots” on the nape (back) of the neck. The most notable distinguishing markings are two black mustache mark features, one on each side of their face. The American Kestrel has large dark eyes and yellow to orange legs, cere, and eye-rings.
The species exhibits sexual dichromism, that is, males are more brightly colored than females. Adult females have a pale buff-colored breast streaked with brown and are rust-brown on their nape, back, and wing coverts (small feathers covering insertion points of larger feathers). Their back and wing coverts are heavily barred with black, as are their rust-brown tails which terminate with a narrow white band. Adult males have a rust patch on the crown and a rust nape, breast, back, and tail. They have a pale belly and blue-gray wing coverts. Their dark flight feathers terminate with pale spots, creating a “string of pearls” effect. They also have black spots on their wings and flanks. Their tail ends in a wide black border tipped in white, rust, or blue-gray.
American Kestrels consume a gamut of small prey. Insects such as grasshoppers, crickets, and butterflies are a major part of their summer diet which also includes mammals such as mice, voles, shrews along with juvenile squirrels and rabbits. Small birds, lizards, snakes, toads, and frogs are a smaller part of their prey diet. In the north in winter months they eat mostly birds and mice. They are diurnal, usually hunting in the morning and early evening in summer, and throughout the day in winter.
Foraging for prey, this bird hunts on the wing, flying with rapid wing beats and short glides over open country or circle above, often stopping in mid-air if it sees something of interest on the ground. When a meal is spotted, the American Kestrel partially folds its wings, drops lower, and swoops to the ground to grasp the mouse or insect with sharp talons Then the raptor flies to a perch to swallow small insects whole or, holding larger prey with both feet, to use the sharp beaks to rip and tear off pieces of flesh.
Breeding takes place in the spring (in California from April to June). Male kestrels display to attract females by climbing high, calling, then diving fast and steeply before climbing again repeatedly. Kestrels do not build nests. While they usually use tree cavities, holes in cliffs, and woodpecker holes as nurseries, they also may occupy abandoned nests of other birds, nest boxes, and even crevices of buildings. Males influence females in the selection of the nesting site and then defend the nesting territory; in turn, the female defends the actual nest itself.^
Females lay three to seven cream, white, or pale pink 35 mm (1.4 in) eggs that can be splotched with brown. For the next 29-31 days the female does most of the incubation while the male hunts to feed her. He calls her to come out of the nest hole to eat. It takes three to four days for all of the eggs in the clutch to hatch. The chicks are born covered with down but with closed eyes. Chicks do not compete with each other for food. At first they are fed by the female and later by both parents. They fledge when 28-31 days old. The fledglings return to the nest at night for about two weeks before becoming independent. In certain cases a number of juveniles will leave the breeding area and form a separate flock. American Kestrels in the wild have a typical life span of two to five years.
American Kestrels are territorial and normally solitary, except during breeding, migrating, or when taking advantage of a rich food source. In winter, males and females defend separate territories, and the sexes have different habitat preferences. Males defend habitat with dense vegetation, whereas females select more open areas. Both aggressively defend their territories against intruders.
In the fall birds that nest in extreme northern areas migrate south to the southern United States and Mexico for the winter. The rest are mostly resident, staying in their territories all year, some in pairs.
Female Kestrels are larger than males, a form of reverse size sexual dimorphism. Sexual dimorphism is a morphological or genetic difference between sexes of the same species. This size difference in Kestrels may allow the same pair of birds to hunt two different ecological niches with different-sized prey. Also, females typically defend the nests and are better able to incubate their eggs because they are larger.
These birds have developed the ability to tolerate the high summer desert temperatures without needing a source of drinking water. They get moisture from their carnivorous diet of mice, birds, and reptiles.
The American Kestrel is currently widely distributed and locally abundant. However, loss of open space due to construction has sharply reduced nesting and foraging habitat in some areas. Electrical lines, wind farms, collisions with vehicles, poisoning, shooting, and trapping are among the dangers for these birds. Researchers are now concerned that mobile phone antenna towers may be an added danger.
American Kestrels play a pivotal important role in the control of certain species such as rodents and insects, major prey elements in their diet. The designation of nuisance prey is generally applied to animals that, in the perception of humans, have become too numerous as a result of the animal's population density, with large numbers causing associated negative human-wildlife or wildlife-wildlife interactions; however, this designation of such prey is generally due to local overpopulation of some of these rodent and arthropod populations, which increases are often the result of anthopogenic forced changes in a given ecosystem.
- ^ IUCN Redlist of Threatened Species. 2009. Falco sparverius
- ^ Aquarium of the Pacific. 2010
- ^ Diego Cisneros-Heredia. 2006. Notes on breeding, behaviour and distribution of some birds in Ecuador. Bull. B.O.C. 126(2): 153-164
- ^ Paul R. Ehrlich, D. Dobkin and D. Wheyte. 1988. The Birder's Handbook: A Field Guide to the Natural History of North American Birds. Simon & Schuster Inc., New York. ISBN 0-671-65989-