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The
American Kestrel and Iowa’s Nest Box Program
Placing
nest boxes along
Iowa’s
state and interstate highways
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Species Description:
American Kestrel Falco
sparverius
Click on any of the links below to learn more. Ecological importance and value The
American kestrel (Falco sparverius) is the smallest and most
colorful member of the falcon (Falconidae) family in North America, and
with the exception of the Seychelles kestrel, the world.
It is roughly the size of a robin or blue jay. The
American kestrel was once called the “sparrow hawk.” However, the name
was changed because the diet of a Falco sparverius is not even close to
being exclusively made up of sparrows. And, technically, the kestrel is a falcon not a hawk.
Falcons have long, pointed wings, rapid wing strokes, and they
usually do
not soar as much as hawks. The
name kestrel is likely derived from the Old French word “cresserelle,”
which means crest and refers to the reddish-brown back and crown patch. Because of their choice of food, kestrels are abundant in agricultural areas characterized by scattered woodlots and trees, shelterbelts, meadows, highway rights-of-way, pastures, and hay fields. Kestrels are frequently seen sitting on power lines along highways or hovering above the grassy roadside ditches. From their location they dive to the ground to catch their prey. Ecological
Importance and Value The
American kestrel is very important ecologically in controlling creatures
humans usually consider a nuisance and destructive (rodents and large
insects). As
attractive members of the falcon family, they are an interesting and
aesthetically pleasing component of our natural world, especially to those
who take the time to enjoy their hovering and diving techniques. The
average kestrel weighs anywhere from 3-6 ounces (females are slightly
larger than males), is 9-12 inches long and has a wingspan of 20-24
inches. Kestrels have been
clocked at speeds of nearly 40 mph. Kestrels
have long, narrow, pointed wings; a short, dark, hooked and notched beak;
dark eyes; and unfeathered legs.
Photo
credit: Used with permission
of the Chipper Woods Bird Observatory The
American kestrel is easily identified by two distinct black streaks
(moustaches or sideburns) on each side of the head that contrast with the
white throat and cheeks. It is the only North American raptor with
circular nostrils. The
eyes of the kestrel face forward, providing the bird great depth
perception and enabling it to prey on its favorite foods.
The kestrel’s eyes are far superior to the human eye.
They are sensitive to light in the near ultra-violet spectrum and
can see details at greater distances, allowing the bird to see the trail
of a rodent on the grass. The
voice is a shrill, high pitched, “klee” call in three to six short,
rapid bursts.
Photo
credit: Courtesy of the Cornell
Lab of Ornithology Sexes
are distinguished by their coloration. Adult males The
adult males have a rust patch on their crown; rust nape, breast, and back;
rust tail with a broad black band midway down and a narrow white band at
the end; pale belly; blue-gray wing coverts; dark flight feathers with
pale spots midway on the feathers creating a “string of pearls”; and
black spots on scapulars, wing coverts and flanks.
Photo
credit: Courtesy of the USGS Patuxent Wildlife Research Center Adult females The
adult female kestrel can be identified by the pale buff breast streaked
with brown; rust-born nape, back and wing coverts; back and wing coverts
barred heavily with black; and rust-brown tail with numerous dark bars of
even width and a narrow white band at the end.
Photo
credit: Courtesy of the University of Minnesota’s Raptor Center Juvenile birds Both
sexes retain juvenile wing and tail feathers until their second summer,
molting them after their first breeding season.
Immature males up to a year old can be recognized by the rust-brown
back barred heavily with black and a streaked breast, and females by a
more poorly defined band midway on the tail.
The
kestrel has two unique characteristics that set it apart from other
diurnal (daytime active) raptors or birds of prey, such as hawks, eagles
and falcons. First,
the kestrel nests primarily in tree cavities that have been excavated by
woodpeckers. This differs
from other diurnal raptors that build open platform nests. Second,
a kestrel hunts from a conspicuous perch or by hovering in the air, then
diving down to catch its prey on the ground. The flight is buoyant,
graceful and rapid, like a large swallow. Watching kestrels hunt can be an
interesting experience. The
American kestrel is, for the most part, not a social bird.
During the mating season, males and females pair up and have joint
territories. Presumably, the pair or the male defends the territory.
The function of the territory may not be so much to ensure mating
as to maintain a pair bond during the nesting season when the male is
needed to help rear the offspring. The
kestrel is widely distributed throughout the United States.
American kestrels live in North, Central and South America from the
tree line boundary in Alaska and Canada south to Tierra del Fuego,
Argentina. The bird can also
be found in the West Indies, the Juan Fernandez Islands and Chile.
In
1982 the U.S. Fish and Wildlife Service researchers estimated the
population of the American kestrel was 2.4 million birds, and appeared to
be stable or even increasing throughout its range.
Little recent information has been available to assess the current
population status throughout most of its range.
The
American kestrel nests in tree cavities, woodpecker holes, crevices of
buildings, holes in banks, and nest boxes.
The kestrel is highly adaptable and lives just about everywhere as
long as there is some open ground for hunting and places on which to perch
(e.g. telephone or fence wires). While
they prefer open country, kestrels will inhabit unforested mountainsides
up to 1300 feet, grasslands, savannas, deserts, farmlands, some coastal
regions, and even suburban and urban environments. The
presence of trees (alive or dead) that contain adequate nesting cavities
is an important component of the kestrel’s habitat.
The other two basic components of a suitable habitat are: (a) an
adequate amount of open pasture-like area of short vegetation with
scattered perch sites; and (b) an adequate prey supply. The
territory size of an American kestrel varies dependent upon habitat
quality (e.g., prey abundance and nest site availability). Researchers
have reported territory size ranging from 124 to 783 acres, with an
average of one breeding pair per mile. In
winter, males and females separate territories, and the sexes have
different habitat preferences. Males
defend habitat with dense vegetation, whereas females select more open
areas. Those
birds in the northern most parts of the geographical range migrate, while
other populations are less migratory. Populations south of approximately
35°N (same latitude as Memphis,Tenn.) are, for the most part, permanent
residents. While
information on migratory movement in Iowa is not well known, band returns
from Iowa-banded kestrels provide some insight. It appears that Iowa's kestrel
population probably contains a mixture of birds that nest in Iowa but
winter to the south, birds that winter in Iowa but nest farther north, and
those that are year-round residents.
American
kestrels are classified as generalist predators.
Its diet varies, but sparrows and other small nesting birds make up
a fair percentage (10 percent) of its prey.
Kestrels have been observed feasting on Red-winged blackbirds and
Common Grackle nestlings, which they take directly from the nest after
having observed the dutiful parents carrying food to the nest for their
young. The starling also ranks high on the kestrel’s menu.
In
addition to eating small birds, kestrels prey on small mammals such as
bats, shrews, rats, gophers, young ground squirrels, meadow voles, deer
mice, and young cottontail rabbits. About 70 percent of the kestrel’s diet consists of mammals. Kestrels
also consume large insects or invertebrates (20 percent of diet);
grasshoppers, crickets, beetles and cicadas are most favored.
Other known prey items include worms, dragonflies, caterpillars,
flies, and spiders. The
remaining 1 percent of the kestrel’s diet consists of reptiles and
amphibians, such as snakes, sandpiper chicks, lizards, and scorpions. In
the summer, American kestrels hunt in the early morning and evening eating
large insects. Kestrels
apparently are able to capture insects more readily then other prey items.
During winter, they hunt throughout the daylight hours and eat small
mammals. Kestrels
obtain an adequate supply of water from the prey items consumed and
therefore do not require a free source of water. Kestrels
use a variety of prey capture techniques including perch hunting, hover
hunting, and foraging on foot. Prey are typically captured with the feet and killed with the
beak, although small insects are often captured and carried with the beak.
American
kestrels are typically monogamous (mate with one bird at a time). Pair bonding is
strong and often is permanent. Pairing
begins up to six weeks before egg laying. Pair formation is initiated by
the male establishing a nesting territory and female associating and
hunting with the territorial male. Males often select the same territory that was used the
previous year. The female may move among several territorial males before
choosing a mate. The
male, or sometimes the female, will try to attract or court a potential
mate's attention by exhibiting a series of power dives from high above the
territory. During the
dive-display, the male performs a series of climbs and dives with three to
five high-pitched notes uttered near the highest point of each ascent. The
dive consists of a vertical drop of 33 to 66 feet, and frequently occurs
directly above the perched female. Pairs
form, courtship feeding (when the male presents food to the female) occurs
and the pair mate frequently until egg laying. Both
sexes have been observed searching for suitable nest sites, however, it is
primarily initiated by the male. American kestrels are almost exclusively
cavity nesters and will use a natural hole in a tree, a woodpecker's hole,
a nest box, a cavity in a bank or cliff, or an enclosed space in a
building. On rare occasions, kestrels may use an old stick nest of another
bird, especially the enclosed nests of magpies. They may even evict
current residents of desirable nest sites.
American
kestrel egg Photo
credit: Courtesy of the USGS Patuxent Wildlife Research Center Eggs
are deposited directly on any debris present on the cavity floor; no
nesting material is brought into the cavity.
Egg color ranges from white to cream, or pale pink to
reddish-brown, usually covered with reddish-brown or gray spots/specks. Generally,
four to five eggs are laid at one- to two-day intervals.
Laying dates vary by geographical area of the world.
In Iowa, egg laying normally begins in late April to early
May. If the first nesting is unsuccessful, kestrels often renest. American kestrel incubating eggs in a nest box. Photo credit: Courtesy USGS, Northern Prairie Wildlife Resource Center Incubation
generally begins with the second to the last egg laid, and lasts 29 to 31
days. The female does the majority of the incubation, with the male
providing her with food. Males have been known to occasionally assist with
incubation by sitting on the eggs. Both sexes have brooding patches. Hatching
occurs over a period of three to four days.
The young nestlings are pink skinned and covered with short,
silvery down at first, but become well feathered by 20 days of age. Once
hatched, kestrel chicks are tended by both parents. The female broods and
feeds the young for about the first 10 days, and the male is the primary
hunter.
The
female leaves the nest one to two weeks after the eggs hatch and assists
the male with feeding the young. The young grow rapidly, attaining their adult weight in 16 to
17 days. Fledging (leaving
the nest) occurs at 28 to 31 days after hatching, but the young will
return to the nest at night to roost.
After
nest departure, the siblings and parents remain as a unit for some time,
often hunting together. The
young remain dependent on their parents for food for two to three weeks
after leaving the nest. The survival rate of chicks is about 50 percent
under natural conditions, but is usually higher under better conditions
(e.g., human-provided nesting boxes.) Life ExpectancyThe average life expectancy of an American kestrel is approximately 15 months. They can live up to six years in the wild, but most suffer a fatality in the second year of life, usually in the fall. In captivity, kestrels have lived from 14 to 17 years. Now that you've learned about the uniqueness of the American kestrel, why not get involved in the Iowa's American kestrel nest box program. To learn more click, on the program link.  |
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