Falco sparveriusAmerican kestrel

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Geographic Range

American kestrels (Falco sparverius) are widespread throughout the Americas. The geographic range of these falcons stretches from Alaska southward to the southern tip of South America. They permanently reside in all, or parts of 35 of the 48 contiguous U.S states, the Gulf of California, northwest and central Mexico, and every country in South America except Brazil. They migrate, and are only summer breeding residents of eight northern U.S states including Montana, North and South Dakota, Wyoming, Minnesota, Wisconsin, Michigan, and Maine. During the summer breeding season, they also reside in British Columbia, Alberta, Saskatchewan, Manitoba, New Brunswick, Nova Scotia, the Gulf of St. Lawrence, and parts of Ontario and Quebec in Canada as well as parts of the Yukon, the Northwest Territories, and central Alaska. They are winter residents in eastern Mexico and Central America. (Ardia and Bildstein, 1997; Palmer, 1988)

Habitat

American kestrels are highly adaptable. They can be found in almost every habitat type within their range including fields, cities, deserts, plains, mountains, and tropical lowlands. Their habitat requirements include open ground for hunting, tall perching sites to improve hunting success, and available nesting cavities. They are most commonly found in open habitats and urban environments. (Ardia and Bildstein, 1997; Johnsgard, 1990; Palmer, 1988)

  • Range elevation
    0 to 3690 m
    0.00 to 12106.30 ft

Physical Description

American kestrels are small, sexually-dichromatic falcons. Males exhibit blue-gray wings and crowns, while females have reddish-brown wings and crowns. Juveniles of both sexes closely resemble adult females. Adult males may have no spotting, or light spotting on the plumage of their upper breast, while juveniles have heavy streaking on their upper breast. As opposed to juveniles, adults have streaking in the crown patch on top of their heads. As adults, both sexes exhibit a black and white facial pattern. They both have two prominent black slashes on their face, making them easily distinguishable. Both male and female adult American kestrels have a pointed, sharp beak, the average beak size is 1.2 to 1.4 cm. Their wings and tails are long and pointed, their wingspan ranges from 51 to 61 cm. The average length from the tip of the beak to the tip of the tail is 22 to 31 cm, and their average weight is 80 to 165 g, making them the smallest falcon in North America. American kestrels have large talon-tipped feet and an anisodactyl toe arrangement. (Bird, 1982; Elbroch and Marks, 2001; Negro, et al., 1998; Palmer, 1988; Parrish, et al., 1987; Smallwood, 1989; Stotz, et al., 1996)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    80 to 165 g
    2.82 to 5.81 oz
  • Range length
    22 to 31 cm
    8.66 to 12.20 in
  • Range wingspan
    51 to 61 cm
    20.08 to 24.02 in

Reproduction

American kestrels are monogamous falcons that establish pair-bonds. Courtship begins early in the breeding season, after a nesting site has been established. Copulation can be initiated by either sex, and usually takes multiple attempts before fertilization occurs. Pairs bond with courtship rituals, such as aerial displays and courtship feeding. After a relationship is developed, it becomes strong and usually permanent. Most pairs return to the same nesting sites for consecutive years. (Bortolotti and Wiebe, 1993; Dawson and Bortolotti, 2008; Johnsgard, 1990; Palmer, 1988; Steenhof and Peterson, 2009; Wiebe and Bortolotti, 2009)

Breeding season differs with geographic location, but mostly occurs from early spring to late summer. In North America, the breeding season ranges from mid-April to mid-June. American kestrels are sexually mature as yearlings. Although pairs search for nesting sites together, males often make the final decisions. These falcons choose cavities as nesting sites to protect the brood from potential predators. Common nesting sites include natural tree hollows, rock crevices, and the corners of buildings or other man-made structures such as telephone poles and fence posts. They typically raise one brood per season, but can raise two if the first brood is unsuccessful. Their average gestation period is 30 days. One brood consists of 3 to 7 eggs, with an average of 4 or 5. Fledging occurs about 30 days after hatching, and they become independent from their parents about three weeks after fledging. (Bortolotti and Wiebe, 1993; Dawson and Bortolotti, 2008; Johnsgard, 1990; Palmer, 1988; Wiebe and Bortolotti, 2009)

  • Breeding interval
    American falcons breed once yearly.
  • Breeding season
    Their breeding season may vary with their range, but most populations breed in the early spring to late summer.
  • Range eggs per season
    3 to 7
  • Average eggs per season
    5
    AnAge
  • Range time to hatching
    26 to 32 days
  • Average time to hatching
    30 days
  • Range fledging age
    28 to 32 days
  • Range time to independence
    28 to 32 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

American kestrels have distinct sex roles during reproduction. Females perform incubation duties more often than males, but males have been known to incubate in the absence of the female. Male kestrels provide food for the mother and offspring from the time she lays eggs until the mother begins to hunt on her own when her offspring are around 10 days old. After hatching, females protect their young and remain near the nest, while males are increasingly absent from the nest. Offspring are born with a white downy coat and pink skin. Kestrels are born altricial, and are therefore dependent on parents for food and protection. This dependence lasts about three weeks after fledging, when offspring are self-sufficient. (Bortolotti and Wiebe, 1993; Johnsgard, 1990; Palmer, 1988; Wiebe and Bortolotti, 2009)

Lifespan/Longevity

American kestrels live an average of 5 years and 2 months in captivity. In the wild, their life expectancy is an average of 1 year and 3 months. The oldest recorded bird in the wild was 11 years. In captivity, these falcons have lived up to 17 years. Most deaths are caused by human interference such as illegal hunting and trapping. Kestrels are also killed in traffic or by predators. Some die of fatal diseases or abnormalities. (Clapp, et al., 1982; Monoghan and Metcalfe, 2000; Palmer, 1988; Roest, 1957)

  • Average lifespan
    Status: wild
    11 years
  • Average lifespan
    Status: captivity
    17 years
  • Typical lifespan
    Status: wild
    0 to 11 years
  • Average lifespan
    Status: wild
    1 years
  • Typical lifespan
    Status: captivity
    0 to 17 years
  • Average lifespan
    Status: captivity
    5 years

Behavior

American kestrels are solitary birds, with the exception of pair-bonding during mating season. They are the only North American falcon with a flight pattern characterized by rapid wing beats and short glides. Aggressive encounters between birds can occur over prey, territory, and nesting sites. These aggressive displays usually involve circling and diving at the opponent, while making loud calls. Ultimately, one bird forfeits and flees the scene. These falcons bathe in standing water or during rain showers, but are also known to take dust baths by splashing dust with their wings to cover their body. This helps to reduce the prevalence of ectoparasites. (Bird and Negro, 1996; Johnsgard, 1990; Palmer, 1988; Rudolph, 1982)

  • Average territory size
    4.5-5.2 km^2

Home Range

Their home range depends on the available nesting sites and resources, but ranges from 4.5 to 5.2 square kilometers. (Palmer, 1988)

Communication and Perception

American kestrels demonstrate three basic calls – the “klee” or “killy,” the “chitter,” and the “whine”. The most common among these is the “klee,” which is used year-round by both sexes to portray distress or excitement. Adult male and female birds deliver a “chitter” call to the opposite sex, usually during courtship or copulation. This call is social and associated with friendly behavior. The “whine” is associated with feeding behaviors and is used by adults of both sexes and by hungry offspring. They demonstrate all three calls by the age of two weeks. American kestrels also communicate visually through behavioral displays. (Johnsgard, 1990)

Food Habits

American kestrels change their diet seasonally. Their summer diet consists primarily of insects such as grasshoppers, crickets, butterflies, moths, and beetles. During the winter, they hunt small prey such as mice, voles, shrews, snakes, frogs, and small birds. One study in an urban environment found their diet consists of 78% insects, 14% mammals, 6% reptiles and amphibians, and 3% birds. American kestrels are diurnal hunters and exhibit three different hunting methods: hovering, perch-hunting, and in-flight insect catching. They have talon-tipped feet and a sharp beak well-suited for hunting. (Bird, et al., 1982; Brack, et al., 1985; Johnsgard, 1990; Palmer, 1988; Rudolph, 1982)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms

Predation

Because American kestrels are relatively small falcons, they may be preyed on by other raptors including great-horned owls, red-tailed hawks, and prairie falcons. Most predation occurs on eggs, broods, or young birds. The two black spots on the back of their head may act as an anti-predatory adaptation. Predators may be fooled into thinking the back of the head is the face because the black dots resemble eyes. Other known predators include bobcats, skunks, coyotes, and raccoons. This falcon’s greatest defense mechanism against predators is their keen eyesight. (Johnsgard, 1990; Palmer, 1988)

Ecosystem Roles

American kestrels are known hosts for multiple parasitic species including: trematodes (Ascocotyle felippei), mites (Epoplichus minor), nematodes (Baruscapillaria falconis), and protozoa (Plasmodium relictum). Plasmodium relictum is the cause of avian malaria in American kestrels. Falcons also aid seed dispersal and pollination of some plants by eating seeds, and spreading them throughout their community. They also play an important predator role within their ecosystems by controlling prey populations. (Gonzalez-Acuna, et al., 2011; Medica, et al., 2007)

  • Ecosystem Impact
  • disperses seeds
  • pollinates
Commensal/Parasitic Species
  • trematodes (Ascocotyle felippei)
  • mites (Epoplichus minor)
  • protozoans (Plasmodium relictum)
  • nematodes (Baruscapillaria falconis)

Economic Importance for Humans: Positive

American kestrels are kept and trained by humans for falconry. In the United States, American kestrels and red-tailed hawks are the only birds permitted to be used by beginner falconers. These birds are used to hunt rodents, insects, and small birds. American kestrels are also commonly used in scientific research because they are easily bred in captivity. These falcons are considered useful to humans, especially farm owners, because they eat pest species. Because West Nile virus afflicts birds and humans, American kestrels are used by public health officials to detect West Nile Virus outbreaks. Sick or dead birds are an early warning signal that the virus is present in a population. (Bird, 1982; Medica, et al., 2007)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

American kestrels occasionally pursue small domesticated animals and pets as prey including chickens, cats, and small dogs. (Bird, 1982)

Conservation Status

American kestrels are a species of least concern globally and are not listed as a species of concern in the United States. Their estimated world population is greater than 1,000,000 and remains stable. Due to their large and stable population, conservation actions are not required at this time. (BirdLife International, 2012; Strasser and Heath, 2013)

Other Comments

American kestrels were formerly known as American sparrow hawks. They were officially renamed in 1983 by the American Ornithologist's Union. (Palmer, 1988; Roest, 1957)

Contributors

Sutton Townes (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Ardia, D., K. Bildstein. 1997. Sex-related differences in habitat selection in wintering American kestrels, Falco sparverius. Animal Behavior, 53: 1305-1311.

Bird, D. 1982. The American kestrel as a laboratory research animal. Nature, 299: 300-301.

Bird, D., S. Ho, D. Pare. 1982. Nutritive values of three common prey items of the American kestrel. Comparative Biochemistry and Physiology, 73A/3: 513-515.

Bird, D., J. Negro. 1996. Social behavior of captive fledging American kestrels (Falco sparverius). Journal of Raptor Research, 30/4: 240-241.

BirdLife International, 2012. "Falco sparverius" (On-line). IUCN Red List of Threatened Species. Accessed November 01, 2013 at http://www.iucnredlist.org/details/22696395/0.

Bortolotti, G., K. Wiebe. 1993. Incubation behaviour and hatching patterns in the American kestrel (Falco sparverius). Ornis Scandinavica, 24/1: 41-47.

Brack, V., T. Cable, D. Driscoll. 1985. Food habits of urban American kestrels. Zoology, 94/1: 607-613.

Clapp, R., K. Klimkiewicz, J. Kennard. 1982. Longevity records of North American birds: Gaviidae through Alcidae. Journal of Field Ornithology, 53/2: 81-208.

Dawson, R., G. Bortolotti. 2008. Experimentally prolonging the brood-rearing period reveals sex-specific parental investment strategies in American kestrels (Falco sparverius). The Auk, 125/4: 889-895.

Elbroch, M., E. Marks. 2001. Bird Tracks & Sign - A Guide to North American Species. Machanicsburg, PA: Stackpole Books.

Gonzalez-Acuna, D., E. Lohse, A. Cicchino, S. Mironov, R. Figueroa, K. Ardiles, M. Kinsella. 2011. Parasites of the American kestrel (Falco sparverius) in south-central Chile. Journal of Raptor Research, 45/2: 188-193.

Johnsgard, P. 1990. Hawks, Eagles, and Falcons of North America. United States: Smithsonian Institution.

Medica, D., R. Clauser, K. Bildstein. 2007. Prevalence of West Nile virus antibodies in a breeding population of American kestrels (Falco sparverius) in Pennsylvania. Journal of Wildlife Diseases, 43/3: 538-541.

Monoghan, P., N. Metcalfe. 2000. Genome size and longevity. Trends in Genetics, 16/8: 331-332.

Negro, J., G. Bortolotti, J. Tella, K. Fernie, D. Bird. 1998. Regulation of integumentary colour and plasma carotenoids in American kestrels consistent with sexual selection theory. Functional Ecology, 12: 307-312.

Palmer, R. 1988. Handbook of North American Birds Volume 5. Yale University: Yale University Press.

Parrish, J., J. Stoddard, C. White. 1987. Sexually mosaic plumage in a female American kestrel. The Condor, 89/4: 911-913.

Roest, A. 1957. Notes on the American sparrow hawk. The Auk, 74/1: 1-19.

Rudolph, S. 1982. Foraging strategies of American kestrels during breeding. Ecology, 63/5: 1268-1276.

Smallwood, J. 1989. Age determination of American kestrels: A revised key. Journal of Field Ornithology, 60/4: 510-519.

Steenhof, K., B. Peterson. 2009. Site fidelity, mate fidelity, and breeding dispersal in American kestrels. The Wilson Journal of Ornithology, 121/1: 12-21.

Stotz, D., J. Fitzpatrick, T. Parker, D. Moskovits. 1996. Neotropical Birds: Ecology and Conservation. United States: The University of Chicago Press.

Strasser, E., J. Heath. 2013. Reproductive failure of a human-tolerant species, the American kestrel, is associated with stress and human disturbance. Journal of Applied Ecology, 50: 912-919.

Wiebe, K., G. Bortolotti. 2009. Egg size and clutch size in the reproductive investment of American kestrels. Journal of Zoology, 237/2: 285-301.

Wiehn, J., E. Korpimaki, K. Bildstein, J. Sorjonen. 1997. Mate choice and reproductive success in the American kestrel: A role for blood parasites?. Ethology, 103: 304-317.