The American kestrel (Falco sparverius) is the smallest and most common falcon in the Americas. Though it has been called the American "sparrow hawk", this now obsolete vernacular name is a misnomer; the American kestrel is a true falcon, while neither the Eurasian sparrowhawk nor the other species called sparrowhawks are in the family Falconidae, hence only very distantly related to the American kestrel. It has a roughly two-to-one range in size over subspecies and sex, varying in size from about the weight of a blue jay to a mourning dove. It is a very successful species, occurring almost throughout North and South America except for the Arctic fringes of North America, and the densest tropical Amazon rainforest areas; it has evolved into 17 subspecies adapted to different environments and habitats throughout the region. It exhibits sexual dimorphism in size (females being moderately larger) and plumage, although both sexes have a rufous back with noticeable barring. Its plumage is colorful, and juveniles are similar in plumage to adults.
The American kestrel usually hunts in an energy-conserving fashion by perching and scanning the ground for prey to ambush, though it also hunts from the air. It sometimes hovers in the air with rapid wing beats while homing in on prey. Its diet typically consists of grasshoppers and other insects, lizards, mice, and small birds (e.g. sparrows). This broad diet has contributed to its wide success as a species. It nests in cavities in trees, cliffs, buildings, and other structures. The female lays three to seven eggs, which both sexes help to incubate.
Its breeding range extends from central and western Alaska across northern Canada to Nova Scotia, and south throughout North America, into central Mexico and the Caribbean. It is a local breeder in Central America and is widely distributed throughout South America. Most birds breeding in Canada and the northern United States migrate south in the winter. It is an occasional vagrant to Western Europe.
The American kestrel is often used in falconry, especially by beginners. Though not as strong a flyer as many other, larger falcons, proper training and weight control by the falconer can allow captive American kestrels to become effective hunters of birds in the size range of sparrows and starlings, with occasional success against birds up to approximately twice their own weight.Mullenix
Etymology The genus name is from Late Latin meaning "falcon". The specific epithet sparverius is Medieval Latin for a "sparrowhawk".
Until the sixth edition of the AOU Checklist of North American Birds was published by the American Ornithologists' Union in 1983, the most commonly used name for the American kestrel was the sparrow hawk. This was due to a mistaken connection with the Eurasian sparrowhawk in the genus Accipiter. The sixth edition of the AOU Checklist corrected this, officially renaming the bird American kestrel. Several other colloquial names for the kestrel are also in use, including grasshopper hawk, due to its diet, and killy hawk, due to its distinct call.Wauer, p. 4
Taxonomy The American kestrel was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae under the current binomial name Falco sparverius. Linnaeus based his account on the "little hawk" that had been described and illustrated by the English naturalist Mark Catesby in his book The Natural History of Carolina, Florida and the Bahama Islands that was published between 1729 and 1732. Linnaeus specified the type locality as America but this was restricted to South Carolina based on Catesby.
Based on appearance and behavior it was for many years considered a member of the primarily European and African kestrel clade within the genus Falco, but DNA analysis shows the American kestrel is instead genetically more closely related to all other falcons, placed basal to all of the "non-kestrel" falcons. Though the species is thus not actually a kestrel in the phylogenetic sense, it has not been renamed as a result of these genetic analyses. A process of convergent evolution to fit a similar ecosystem niche, hunting small, largely ground-dwelling, prey in the same manner as the true kestrels, have left it with similar physical characteristics and hunting methods. The entire genus are all so closely related that most or all can be hybridized by artificial insemination.
Subspecies Seventeen subspecies of the American kestrel are recognized, generally based upon plumage, size, and vocalizations:
+ImageSubspeciesNotesF. s. sparveriusdescribed by Carl Linnaeus in 1758, is the nominate subspecies. It is found in most of the United States, Canada and Mexico.F. s. paulusdescribed by Howe and King in 1902, is found in the southeastern United States from Louisiana to Florida.F. s. peninsularisdescribed by Edgar Alexander Mearns in 1892, is found in southern Baja CaliforniaF. s. tropicalisdescribed by Ludlow Griscom in 1930, is found from southern Mexico to northern HondurasF. s. nicaraguensisdescribed by Howell in 1965, is found in Honduras and NicaraguaF. s. sparverioidesdescribed by Nicholas Aylward Vigors in 1827, is found on Cuba, Isla de Juventud and the central and southern BahamasF. s. dominicensisdescribed by Johann Friedrich Gmelin in 1788, is found on Hispaniola (both the Dominican Republic and Haiti) and JamaicaF. s. caribaearumdescribed by Gmelin in 1788, is found on Puerto Rico and throughout the Lesser Antilles to GrenadaF. s. brevipennisdescribed by Hans von Berlepsch in 1892, is found in the Netherlands AntillesF. s. isabellinusdescribed by William Swainson in 1837, is found from Venezuela to northern BrazilF. s. ochraceusdescribed by Charles B. Cory in 1915, is found in northwestern Venezuela and eastern ColombiaF. s. caucaedescribed by Frank Chapman in 1915, is found in western ColombiaF. s. aequatorialisdescribed by Mearns in 1892, is found in northern EcuadorF. s. peruvianusdescribed by Cory in 1915, is found in southwestern Ecuador, Peru and northern ChileF. s. fernandensisdescribed by Chapman in 1915, is found on the Juan Fernández Islands off ChileF. s. cinnamominusdescribed by Swainson in 1837, is found in Peru, Chile and ArgentinaF. s. cearaedescribed by Cory in 1915, is found from northeastern Brazil south to eastern Bolivia
Description
Under traditional terminology, the American kestrel is the smallest raptor in the Americas, though the South American spot-winged falconet is almost as small.Wauer The American kestrel is sexually dimorphic, although there is some overlap in plumage coloration between the sexes. The bird ranges from in lengthDavis, Kate, Falcons of North America, 2008, Mountain Press Publishing Company, , Kindle Edition, Location 2232. with a wingspan of . The female kestrel is larger than the male, though less so than larger falcons, being typically about 10% to 15% larger within a subspecies. The more northern subspecies tend to larger sizes (northern hemisphere), with a large northern female being about twice the size of a small southern male. The male typically weighs , and the female . In standard measurements, the wing bone is long, the tail is and the tarsus is .American Kestrel, Life History, All About Birds – Cornell Lab of Ornithology. Allaboutbirds.org. Retrieved 2013-02-25.
Physically, American kestrels are leaner and less muscular than larger falcons.Mullenix, Matt (2003) Merlins and American Kestrels Compared. merlinfalconry.com. The pectoral flight muscles of the American kestrel make up only about 12% of its body weight, as compared to about 20% for the strongest flying falcons such as the peregrine falcon.Davis, Kate, Kindle locations 225–234. The wings are moderately long, fairly narrow, and taper to a point. Their less muscular body type is adapted to energy-conserving ambush hunting, rather than spending large amounts of energy-consuming time on the wing and getting into long tail-chases of bird prey. For their size, they have strong talons and beaks, and can swiftly dispatch prey. Their lean build and energy-conserving strategy allow a lower daily food intake than if they were more strongly muscled, yet with enough strength to commonly take bird prey as large as themselves, and occasionally larger. The success of this body style and hunting strategy is reflected in the high success of the species in densely populating a large range throughout the Americas. The flight of the American kestrel is not so dramatic and swift as more muscular falcons such as merlins and peregrines, but their efficient adaptation to a broader diet of more available smaller prey, and need for less food per day, has resulted in their greater population.
In contrast to many other raptor species, the sexes differ more in plumage than in size. Males have blue-gray wings with black spots and white undersides with black barring. The back is rufous, with barring on the lower half. The belly and flanks are white with black spotting. The tail is also rufous, with a white or rufous tip and a black subterminal band. The back and wings of the female American kestrel are rufous with dark brown barring. The undersides of the females are creamy to buff with heavy brown streaking. The tail is noticeably different from the male's, being rufous in color with numerous narrow dark black bars. Juveniles exhibit coloration patterns similar to the adults'. In both sexes, the head is white with a bluish-gray top. There are also two narrow, vertical black facial markings on each side of the head, while other falcons have one. Two black spots (ocelli) can be found on each side of the white or orangish nape. The function of these spots is debated, but the most commonly accepted theory is that they act as "false eyes", and help to protect the bird from potential attackers.
Vocalizations The American kestrel has three basic vocalizations – the "klee" or "killy", the "whine", and the "chitter". The "klee" is usually delivered as a rapid series – klee, klee, klee, klee when the kestrel is upset or excited. This call is used in a wide variety of situations and is heard from both sexes, but the larger females typically have lower-pitched voices than the males. The "whine" call is primarily associated with feeding but is also uttered during copulation. The "chitter" is used in activities that involve interaction between male and female birds, including courtship feeding, copulation, and the feeding of nestlings.Wauer, pp. 11–12 Nestlings can produce calls similar to those of adults at 16 days old.
Ecology and behavior
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,Wauer, p. 15 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.