American Kestrel Facts
Order Falconiformes, Family Falconidae
- Falcons are the more streamlined of the raptor species, with long pointed
wings bent back at the wrists and large tails that taper at the tips. They
consume numerous kinds of animals including insects, reptiles, small mammals,
and birds. It is also called sparrow hawk, although birds are not the main prey
item. Falcons, in general, have long, pointed wings and long tails, like
mourning dove (Zenaida macroura).
Falcons are found in a variety of
habitats, from cities to the most remote areas. Strong fliers that achieve high
speeds, falcons’ range in size from the American kestrel 27 cm bill tip to tail
tip to the peregrine falcon 41 to 51 cm. It is one of the smallest and most
widely distributed falcons in North America. In the first sight, kestrels are
often confused with other small birds such as mourning doves.
Nest of American
Kestrel
The American Kestrel
seek ready-made nests, such as wild woodpecker excavated holes or
nest boxes provided by humans. Especially- ready-made nest boxes support
kestrels throughout the areas where there are few natural cavities. They
prefer cavities in large trees, crevices in rocks, nooks in structures.
Mainly surrounded by large open areas covered
with short ground vegetation with adequate hunting perches close by. The
Kestrel used nest boxes, but competition from non-native European
Starlings is a real problem. Once the Kestrels pair select the site for
nesting, then they use it for many years.
Selected species
The American kestrel (Falco sparverius), or sparrow hawk, is the
most common falcon in open and semi-open areas throughout North America. There
are three recognized subspecies.
1. F.s. paulus (This is a year-round
resident from South Carolina to Florida and southern Alabama).
2. F.s. peninsularis (it is a year-round
resident of southern Baja California).
3. F.s. sparverius (It is widespread and
migratory).
The Predators of the kestrel include
large raptors such as great horned owls, golden eagles, red-tailed hawks,
coyotes, bobcats, skunks, raccoons, ravens, and crows.
Body size of American Kestrels
The bird weighing slightly over
one-tenth of a kilogram, the kestrel is the smallest falcon native to the
United States. As for most raptors, females are 10 to 20 percent larger than
males. Kestrel body weights vary seasonally, with maximum weight (and fat
deposits) being achieved in winter and minimum weights in summer.
American Kestrels Habitat
Kestrels inhabit open deserts,
semi-open areas, the edges of groves and even cities. In several areas,
investigators have found that male kestrels tend to use woodland openings and
edges, while females tend to utilize more open areas characterized by short or
sparse ground vegetation, particularly during the winter. In other areas,
however, investigators have found no such differentiation.
In Florida, kestrels appear to prefer sandhill communities
particularly pine/oak woodlands. These areas provide high-quality foraging
habitat and most available nest sites. Kestrels are more likely to use habitats
close to centers of human activities than are most other raptors.
Territory size of American Kestrels in relation to relatively
small mammal abundance at the trap site probably reflects a reasonable estimate
of prey availability at all nearby sites. American Kestrels may not alter territorial boundaries once established, particularly if the original territory maximizes rates of prey capture while minimizing costs associated with territorial defense.
American Kestrels Diet
Kestrels prey on a variety of small
animals including invertebrates such as worms, spiders, scorpions, bats, and
beetles. The other large insects, amphibians, and reptiles such as frogs,
lizards, and snakes, and a wide variety of small-to-medium-sized birds and
mammals.
Large insects, such as grasshoppers,
are the kestrels' primary summer prey. Although in their absence kestrels will
switch to small mammals and birds. In winter, small mammals and birds comprise
most of the diet. Kestrels usually cache their vertebrate prey, often in clumps
of grass or in tree limbs and holes, to be retrieved later.
Invertebrate prey usually is eaten
immediately. In Florida, where small mammals are scarce, and reptiles are
abundant, lizards are an important component of the diet. Kestrels forage by
three different techniques: using open perches from which to spot and attack ground
prey, hovering in the air to spot ground prey, and catching insects on the
wing.
Also, some favorite prey, like voles
and mice, leave urine trails that show up in ultra-violet light. They use these
trails to track the hapless rodents. Hence, after a hearty meal, Kestrel stash
leftovers in clumps of grass, bushes, fence posts, tree limbs or tree cavities.
Molt
Females begin their molt during
incubation and complete it by the end of the breeding season. Males, who are
responsible for capturing most of the prey for the family, do not begin their
molt until near the end of the breeding season.
Migration
The American kestrel is a year-round
resident over most of the United States but is migratory over the northern-most
portions of its range (National Geographic Society. Because of their late molt,
males migrate and arrive at the wintering grounds later than females or
immatures.
Breeding activities and social
organization
Adult kestrels are solitary, except
during the breeding season, and maintain territories even in winter. Kestrels
typically build their nests in tree cavities but have used holes in telephone
poles, buildings, or stream banks when tree cavities are not available.
Both parents participate in incubation,
but the female performs most of the incubation, while the male provides her
with food. Following hatching, the male brings most of the prey to the
nestlings. After fledging, young kestrels remain dependent on their parents for
food for at least 2 to 4 additional weeks.
Fledglings often perch and socialize
with their siblings prior to dispersal. In Florida, resident kestrels (Paulus
subspecies) maintain year-round pair bonds and joint territories. The resident
pairs have a competitive advantage over winter migrants (sparverius subspecies)
in their territories.
Home range and resources
Although some investigators have not
noted territorial defense demonstrated that kestrels defend territories by
introducing captured birds into other birds' territories. Winter foraging
territories range from a few hectares in productive areas to hundreds of
hectares in less productive areas.
Summer breeding territories probably
follow the same pattern. Population density although much smaller than
red-tailed hawks and bald eagles, reported kestrel breeding population
densities can be similarly low 0.0003 to 0.004 nests per hectare.
Population Dynamics
Kestrels are sexually mature in the
first breeding season after their birth. Scarcity of suitable nesting cavities
probably limits the size of kestrel populations in parts of the United States.
Three to four young may fledge per nest per year, but the mortality of juveniles
in the first year is high (60 to 90 percent). Adult mortality can below 12 %
per year.
Similar species
from general references, the peregrine falcon (Falco
peregrinus), a rare resident of woods, mountains, and coasts, preys almost
exclusively on birds. Though uncommon, they can be found wintering in most
states, but rarely breeding. These large falcons are 38 cm) have been
reintroduced in some areas in the United States and have nested in urban
environments.
The merlin (Falco columbarius), larger
(30 cm) than the kestrel, can be found in a variety of habitats but nests in
open woods or wooded prairies. Wintering along coasts and near cities of the
Great Plains, it primarily eats birds.
The prairie falcon (Falco mexicanus) also is a larger bird 39 to 50
cm than the kestrel and inhabits dry, open country and prairies. A year-round
resident of the western United States, prairie falcons prey chiefly on birds
and small mammals.
American Kestrels Call
American Kestrel (falcons) are quite
vocal and have a limited set of calls. However, the familiar one is a repeated
loud, thrilled series of 3-6 klee or killy lasting just over a second. The
Kestrels call is distinctive and an excellent way to find these birds.
Moreover, they do not need to drink free-standing water, as they need from the
moisture of their prey.
Kestrel Take-Off and Landing
During take-off, the forward speed of
the bird being low, the primary requirement of lift to overcome gravity is
essentially provided by a fast flapping rate which is higher than in normal
forward flight. The amplitude of flapping is also greater.
Similarly, during landing, the speed
being low, the bird's wings must generate the required lift to uphold the
weight and break the forward motion. Therefore, the wings are spread wide and
the flapping motion adjusted. Kestrel also used "reduced span" upstroke in fast
flight. The bird is having the habit of pumping their tail feathers up and down when
perched, particularly after landing.
Sexes
The male
kestrel has a rusty back, blue-gray wings and crown with a rusty cap, and
distinguishing black facial stripes, and lightly spotted underparts. However,
the female is alike, with a rusty back, wings, and breast streaking, but it
does not have the blue-gray markings of the male. Source: CP
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