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.
- Biogeographic Regions
- nearctic
- neotropical
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.
- Habitat Regions
- temperate
- tropical
- terrestrial
- Terrestrial Biomes
- desert or dune
- savanna or grassland
- chaparral
- forest
- rainforest
- mountains
- Other Habitat Features
- urban
- suburban
- agricultural
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.
- Other Physical Features
- endothermic
- bilateral symmetry
- polymorphic
- Sexual Dimorphism
- sexes colored or patterned differently
- male more colorful
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.
- Mating System
- monogamous
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- induced ovulation
- fertilization
- oviparous
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.
- Parental Investment
- altricial
- male parental care
- female parental care
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.
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.
Home Range
Their home range depends on the available nesting sites and resources, but ranges
from 4.5 to 5.2 square kilometers.
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.
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.
- Primary Diet
-
carnivore
- eats terrestrial vertebrates
- insectivore
- 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.
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.
- Ecosystem Impact
- disperses seeds
- pollinates
- 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.
- 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.
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.
Other Comments
American kestrels were formerly known as American sparrow hawks. They were officially
renamed in 1983 by the American Ornithologist's Union.
Additional Links
Contributors
Sutton Townes (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- 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.
- 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.
- 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.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- 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.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- 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.
- 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.
- 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.
- monogamous
-
Having one mate at a time.
- 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).
- 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
- induced ovulation
-
ovulation is stimulated by the act of copulation (does not occur spontaneously)
- fertilization
-
union of egg and spermatozoan
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- 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.
- male parental care
-
parental care is carried out by males
- female parental care
-
parental care is carried out by females
- arboreal
-
Referring to an animal that lives in trees; tree-climbing.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- solitary
-
lives alone
- 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
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
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