BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Falco sparverius | American Kestrel 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - Both sexes of American kestrels are capable of
breeding as yearlings [40].

Breeding season - The breeding season varies depending on geographic
area.  Pairs are sometimes formed from 6 to 14 weeks before laying
begins [40].  In Ontario, laying begins in early April [40].  In
California, American kestrels breed from early April to early September,
with peak activity between early June and late August [54].  In Montana,
courtship begins in May [17] and in Nevada, the breeding season occurs
from April to July [25].  In Florida, the southeastern kestrel generally
begins laying eggs in early or mid-April [7].

Clutch size and incubation - American kestrels generally lay three to
seven eggs [17,54].  They may raise two clutches in one season.  The
second clutch size is generally smaller than the first.  Yearlings lay
repeat clutches less often than do older birds.  American kestrels may
lay an additional clutch if the first clutch is destroyed [40].  The
eggs are incubated for 28 to 30 days [13,17,25,40].

Fledging - Nestlings fledge in 25 to 31 days [13,25,40].  Fledglings
continue to be fed by the parents until feather development is complete,
usually 12 days after nest departure [25,40].  The fledglings may
continue to stay with parents for 30 days or more [40].

Spring migration - Spring migration begins in February from northern
South America and Central America and begins in March in northern
Mexico.  In California, most birds have begun leaving wintering areas by
mid-February.  American kestrels wintering in Florida begin leaving in
February, and almost all have left by April.  In southern states from
the Rockies east, migration occurs from early March through April, and
in northern states mid-March to mid-April.  On the southern Canadian
prairies, most spring migration is in the last 3 weeks of April, but it
continues to about mid-May [40].

Fall migration - The juveniles leave the breeding range before the
adults [40] and mature female American kestrels generally arrive on
their wintering ground before males [46,47].  In warm climates some
adults stay on their breeding territories year-round [25].
Additionally, some American kestrels winter in northern urban areas that
have a year-round food supply and warm roosting places [40].

In Canada and the northern United States, fall migration begins in
September.  Arrival in Florida begins in September and lasts at least
well into October.  American kestrels arrive in southern Central America
south to Panama beginning in mid-October [40].  Southeastern kestrels
stay on their territories year-round [34].

Longevity - American kestrels have been reported to live up to 11 years
[40].  However, most do not live that long. Palmer [40] reported an
annual average survival of 12.6 months, the oldest bird being aged 9
years, 10 months.  Captives at the McGill University colony live an
average of 5 years and 2 months [40].


PREFERRED HABITAT : 
American kestrels occupy a wide variety of open to semiopen habitats,
including farmland and urban areas from sea level up to 13,000 feet
(3,960 m) elevation [29,40].  They generally occur in any habitat that
contains an adequate prey base, perch sites, and (during the nesting
season) nesting sites [40].  In the Sierra Nevada, American kestrels
range up to alpine zones, mountain meadows, and other open areas in late
summer and fall, but winter at lower elevations [54].  In Montana, they
breed at forest edges and in groves, ranging out over adjoining
prairies, croplands, and badlands [40].  In Nevada, the highest
densities of both breeding and wintering American kestrels are often
located near agricultural areas or riparian vegetation that support an
abundant prey base.  Nesting densities in these preferred habitats often
exceeds one pair per square mile [25].  In British Columbia, American
kestrels commonly occupy quaking aspen (Populus tremuloides) groves,
woodland edges, river bottomlands, wooded lakeshores, farmlands, burns,
meadows, orchards, marshes, and bogs [13].

Southeastern American kestrels inhabit mostly open pine forests and
clearings where snags occur [27].  The decrease of isolated or scattered
pine snags in open habitats used by southeastern American kestrels was
closely correlated with the decline in the number of breeding pairs
[50].

Nesting habitat - Nest sites are usually located along roadways,
streams, ponds, or forest edges [15].  Nests may be reused from year to
year.  In Utah, twelve pairs used the same nest site for 2 consecutive
years and eight pairs used the same site again the third year [24].
Southeastern American kestrels often use the same nest site in
successive years [34].  However, Hammerstrom and Hart [23] found that
American kestrels in central Wisconsin did not use the same nest site in
succeeding years even after having raised a brood successfully.

American kestrels prefer to nest in natural cavities with tight-fitting
entrances, or in cavities excavated by other bird species in both live
trees and snags [15,24,29,40].  The diameter of 15 cavity openings used
by American kestrels in British Columbia ranged from 2.5 to 14.1 inches
(6.4-36 cm) [13].  Trees with a d.b.h. greater than 12 inches (30 cm)
are preferred [15].  The species of trees used differs among geographic
regions [13,24,56,58].  Cavities excavated by northern flickers
(Colaptes auratus) and natural cavities located 6.5 to 35 feet (2-10.7
m) above the ground are commonly used as nesting sites [24].  If
cavities are unavailable, American kestrels nest in a variety of sites
including niches in rocky cliffs, under the eaves of buildings, in old
black-billed magpie (Pica pica) nests, in cavities in cacti, in unused
chimneys, or in nest boxes [15,17,24,54].

Herron and others [25] reported that American kestrels in Nevada
generally nest about 20 feet (6 M) from the ground and seem to prefer an
easterly exposure.

Of 41 American kestrel nests in Utah, 28 were located in trees (19 in
old northern flicker holes, two in old magpie nests and seven in natural
cavities).  The species and number of trees used were 18 cottonwood
(Populus spp.), 3 poplar (Populus spp.), 3 willow (Salix spp.), 3 maple
(Acer spp.), 1 elm (Ulmus spp.), and one apple.  Two of the remaining
nests were located in rocky cliffs and the last 11 were found on
building tops [24].  In southeastern Montana and northern Wyoming, most
American kestrel nests were in cavities of ponderosa pine (Pinus
ponderosa) and cottonwood or in sandstone cliffs.  Other nests were in
fenceposts, under bridges, and in abandoned magpie nests.  The greatest
number of nests occurred in ponderosa pine stands.  The mean distance
between occupied nest sites on the survey plots was 0.4 miles (0.7 km)
[56].

In British Columbia, American kestrel nests were situated in woodpecker
holes or natural cavities in living and dead trees (73%), in man-made
structures (23%), and in holes in cliffs.  Sometimes nests of other
species of birds were used, including those of belted kingfishers
(Ceryle alcyon), black-billed magpies, and American crows (Corvus
bachyrhynchos).  Ponderosa pine (29%) and Douglas-fir (Pseudotsuga
mensiesii) (10%) were the most often used species of coniferous trees;
important deciduous trees were black cottonwood (Populus trichocarpa)
(19%) and quaking aspen (8%).  Man-made structures included nest boxes
(17%), buildings, power poles, and fence posts [13].

Nests of southeastern American kestrels are commonly located in old
woodpecker holes in snags 12 to 35 feet (39-114 m) above the ground
[27].  Most nest cavities have been excavated by northern flickers,
red-headed woodpeckers (Melanerpes erythrocephalus), or red-bellied
woodpeckers (Melanerpes carolinus) [58].  In north-central Florida,
southeastern American kestrels nested most frequently in longleaf pine
trees.  Turkey oak and live oak (Quercus virginiana) were also occupied.
Natural cavities occurred solely in turkey oak, whereas all nest
cavities in longleaf pine were of woodpecker origin.  The frequent use
of longleaf pine in this study indicates that this tree species is
particularly important for southeastern American kestrels nesting in
north-central Florida.  Turkey oak snags may be important alternate nest
sites for southeastern American kestrels and may increase in importance
as longleaf pine becomes scarcer [58].

Foraging habitat - American kestrels generally forage in open habitats
that contain high perches [29].  They probably use perch sites in tree
islands and along forest edges.  They also hunt by hovering over areas
of short, open vegetation [15].  American kestrels usually search for
prey from elevated perches such as fenceposts, utility poles and wires,
live trees, snags, and rock outcrops [15,36,40].  They prefer perches 16
feet (5 m) high or higher to perches over 8 feet (2.5 m) high [22].
Fischer and others [20] found that American kestrels wintering in
central Utah predominantly used wire perches.  Poles and trees were used
less often.  In Venezuela, 25 feet (7.6 m) tall poles were more
acceptable for perches than 6 foot tall (1.8 m) poles [40].  

Winter habitat - Winter habitat for American kestrels is generally the
same as nesting habitat, except that high elevation areas are not used
[15,29].  Several studies have found differental habitat use by male and
female adult American kestrels in the southern United States and
northern Mexico.  In areas of winter segregation, females often occupy
the best habitats which often includes open areas covered with short or
sparse ground vegetation.  Males are found primarily in woodland
openings, along woodland edges, or in other less open habitats.  This
differential habitat use may be due to the males arriving on the
wintering grounds later than the females.  The females therefore may
establish their winter territories in the best habitats before the males
arrive [46,47].


COVER REQUIREMENTS : 
American kestrels most often select cavities with tight-fitting
entrances for nests, probably to protect the nest from ground predators
[10].  The need for cover does not seem to affect foraging behavior.
When foraging, American kestrels are commonly found on high, exposed
perches where they can look out over wide stretches of grassland or
pasture to watch for prey [24].  They prefer to hunt in open areas
covered only by short and sparse ground vegetation [12,24].  During the
winter, the availability of shelters may be a limiting factor.  The
distribution of American kestrels wintering in Ohio was closely linked
to availability of old buildings and other sheltered roosts [12].

The thick understory created by pine regeneration in cut or unburned
forests in Florida may have an adverse effect on southeastern American
kestrel populations [26].  


FOOD HABITS : 
American kestrels eat primarily insects during the summer, but also take
mice and other small mammals, birds, lizards, toads, frogs, and small
snakes.  They sometimes eat carrion [15,40,60].  During the winter in
northern latitudes they eat primarily small birds and rodents [17,24].

Invertebrates eaten by American kestrels include earthworms, spiders,
centipedes, scorpions, and insects of seven orders, including both
larvae and adult forms of Diptera, Lepidoptera, and Coleoptera.
Reptiles include five genera of lizards and at least six species of
snakes.  Over 30 species of birds are listed as prey:  They range in
weight from under 10 grams to over 150 grams.  About 30 species of
mammals have also been listed as prey, with a weight range similar to
that of the avian prey [60].  About seven genera of bats are listed as
prey [40].

Some specific prey items of American kestrels include grasshoppers,
dragonflies, crickets, June beetles, weevils, crayfish, snails, small
ground squirrels (Spermophilus spp.), wood rats (Neotoma spp.), pocket
gophers (Geomys spp.), red squirrels (Tamiasciurus hudsonicus),
chipmunks (Tamaia striatus, Eutamias spp.), least weasels (Mustela
rixosa), voles (Microtus spp.), cotton rats (Sigmodon spp.), house mice
(Mus musculus), and shrews (Sorex spp.).  Many house sparrows (Passer
domesticus) are taken in rural and urban areas [40].


PREDATORS : 
Some potential avian predators of American kestrels include great horned
owls (Bubo virginianus), golden eagles (Aquila chrysaetos), red-tailed
hawks (Buteo jamaicensis), and prairie falcons (Falco mexicanus) [39].
Other potential predators that have been reported preying on other
raptor species and their clutches include coyotes (Canis latrans),
bobcats (Lynx rufus), skunks (Mephitis mephitis and Spilogale putorius),
raccoons (Procyon lotor), and crows and ravens (Corvus spp).


MANAGEMENT CONSIDERATIONS : 
Although most American kestrel populations are currently stable or
increasing, there are numerous land use practices that could adversely
affect them [25].  Agriculture, wetland drainage, mineral exploration
and mining, recreational activities, and general urban development can
lead to nest site unsuitability and reduction of prey populations [12].
Additionally, the increased demand for firewood in recent years has
reduced the number of trees which are most suitable for nesting and
perching American kestrels.  Nest cavities excavated by woodpeckers are
seldom present in young stands.  There is also evidence that many of the
pesticides used for insect control adversely affect American kestrel
populations.  Accumulation of pesticide residues in the American kestrel
can result in lowered reproductive success or death of the individual
[25].

The lack of suitable nesting cavities has been suspected to be the
limiting factor for southeastern American kestrels [50].  In areas
formerly dominated by longleaf pine flatwoods in north-central Florida,
southeastern American kestrels have declined an estimated 82 percent
since the early 1940's.  Nest-site availability has decreased
significantly due to widespread logging of longleaf pine, plus the
clearing of isloated longleaf pine trees from agricultural fields.
Along the central Florida ridge in Lake, Orange, and Seminoli counties,
southeastern American kestrels declined with the conversion of the
original longleaf pine-turkey oak communities to citrus groves [26].

Nest boxes can provide nest sites for American kestrels in areas of
declining availability of natural cavities.  Nest box program goals
should include expansion and reestablishment of nesting habitat.  Nest
boxes require continuous maintenance so a program of snag management to
promote natural nest sites should occur along with a nest box program
[22].

Nest boxes are not always the optimal management tool.  Both predation
and parasitism can increase after boxes are installed.  Predator guards
must be installed on wooden poles and trees.  Annual cleaning and
replacement of wood shavings reduces parasite loads.  A major problem
with nest boxes is that European starlings (Sturnus vulgaris) also use
them.  In Iowa, occupied boxes were used by starlings 62 percent of the
time.  If starlings are controlled, American kestrels are more likely to
occupy the boxes [22].
 
American kestrels are fairly tolerant of human activity at the nest and
can be flushed from the nest and even caught on the nest without
abandonment [34].  In Ohio, American kestrels used areas nearer centers
of human activity than did other raptors wintering in the same area
[20].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Falco sparverius | American Kestrel