BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Falco mexicanus | Prairie Falcon 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - Some prairie falcons breed when 1 year old, but
most probably do not begin breeding until 2 years old [16,27].

Breeding season - The breeding season varies depending on geographic
area.  Reproductive activity usually begins in late winter or early
spring.  Courtship and mate selection occur on the breeding grounds at
least 1 month before egg laying [16].  In California prairie falcons
breed from mid-February to mid-September, with peak activity from early
May to early August [34].  In Nevada they arrive on the breeding grounds
in March and lay eggs in March or early April [19].

Clutch size and incubation - Prairie falcons generally lay three to six
eggs.  The eggs are incubated for 29 to 33 days.  If the first clutch is
destroyed another may be laid after 20 to 25 days [27,32].

Fledging - Nestlings fledge in 40 days [32].

Migration - Other than local movements to low elevations, many adult
prairie falcons tend to be residents on their breeding range if there is
an adequate year-round food supply [27,32].  During the nonbreeding
season most juveniles and some adult prairie falcons migrate to the
intermontane valleys and Great Plains [16].  Young prairie falcons in
Wyoming and Colorado often move eastward from mountainous areas to the
plains, where horned larks (Eremophila alpsetris) are numerous [27].
The adults seem to establish winter territories on their winter range
[32].  In north-central Utah migrant prairie falcons usually arrive in
the valleys in late October and remain there until March [27].

Longevity - Prairie falcons may live as long as 20 years; the longest
known banding recovery is 13 years.  Immature mortality has been
estimated to be 75 percent and average annual adult mortality 25
percent.  The average life expectancy of the praire falcon has been
estimated at 2.4 years [16].


PREFERRED HABITAT : 
Prairie falcons occupy open treeless terrain including prairies,
deserts, riverine escarpments, canyons, foothills, and mountains in
relatively arid western regions [13,16,32,34].  In the Sierra Nevada
prairie falcons range above timberline in late summer but winter at
lower elevations [34].

Nesting habitat - During the breeding season prairie falcons are
commonly found in foothills and mountains which provide cliffs and
escarpments suitable for nest sites [16].  Occasionally prairie falcons
nest at altitudes of 10,000 feet (3,048 m), although this is
exceptional. The highest recorded nest site is 11,699 feet (3,566 m) in
Colorado [32].  Prairie falcons generally nest on cliffs, from low rock
outcrops of 30 feet (9 m) to vertical cliffs 400 feet (121 m) high.
They prefer cliffs with a sheltered ledge with loose debris or gravel
for a nest, overlooking treeless country for hunting.  They may also
nest in potholes or large caves [32].  Prairie falcons sometimes use old
nests of ravens (Corvus spp.), hawks, and golden eagles (Aquila
chrysaetos) [8,13,32].  Nest sites with southern or eastern exposures
are preferred.  However, in southwestern Idaho no preference was noted
[16], and in the San Joaquin Valley, California, most prairie falcon
nests had northern exposures and no south-facing ledges were used [32].
Prairie falcons usually have alternate nesting sites located on the same
cliff and tend to use alternate ledges in succeeding years.  Nesting
failure does not seem to deter use of the cliff in the following year
[32].

Of 36 nesting cliffs in Colorado and Wyoming, 14 were sandstone, 10 were
sedimentary conglomerate, 7 were limestone, and 5 were granite.
Twenty-two nesting ledges faced south, five faced north and nine faced
east or west [32].  In southeastern Montana and northern Wyoming,
Phillips and others [28] reported that all prairie falcon nests were
found in cracks or potholes in sandstone cliffs.  The mean distance
between occupied nest sites was 4.8 miles (7.8 km) [28].

In British Columbia prairie falcon nests were situated on ledges, in
caves, in crevices, and in potholes on cliffs.  Nesting cliffs were
granite or sandstone and ranged from 49 to 453 feet (15-138 m) in
height; the actual nest site ranged from 29 to 295 feet (9-90 m) from
the base of the cliff [12].

Foraging habitat - Prairie falcons generally forage in open areas with
low vegetation containing ground squirrels (Spermophilus spp.) and
passerine birds.  They tend to have definite hunting ranges.  When food
is plentiful these areas are confined to the least possible radius
necessary to secure required food supplies [32], but prairie falcons
will forage up to 15 miles (24 km) from the nest [21].  The usual
hunting method consists of flying at a altitude of 50 to 300 feet (15-91
m) and diving at potential prey.  Prairie falcons also hunt from
perches.  Prairie falcons often eat while perched on a convenient
vantage point or on the ground where they have captured their prey [32].
During the breeding season extra food is cached near the nest for
subsequent use [16].

Winter habitat - Winter habitat for prairie falcons is generally the
same as nesting habitat, except that high elevation areas are not used
[27].  In northern Colorado winter ranges (maximum distance between
observation points of individual marked birds) averaged 3.8 miles (6.1
km) for males and 7.2 miles (11.5 km) for females.  The maximum range
was 12.1 miles (919.4 km) for one female [34].


COVER REQUIREMENTS : 
Nests are often recessed in a cliff to provide protection from mammalian
predators, shelter, and shade [1,12,27].  Nests are rarely located at
the top of a cliff [27].  In southwestern Idaho 60 percent of the nests
surveyed were in cavities that afforded some protection for the eggs and
young; 19 percent were on exposed ledges [26].  The need for cover does
not seem to affect foraging behavior.  Prairie falcons prefer to hunt in
open areas covered only by short, sparse ground vegetation [32].


FOOD HABITS : 
Prairie falcons eat a wide variety of prey including mammals, birds,
reptiles, and insects.  In many areas mammals, primarily ground
squirrels, are the major prey item eaten during the breeding season
[16,19,32].  In areas lacking ground squirrels, small- to medium-sized
birds and reptiles are major prey items [16].  The horned lark is the
main food item for prairie falcons wintering in the wheat-growing areas
of the western United States [16,32].

Prairie falcons develop prey preferences and will concentrate on a
single species or group of species exclusively for as long as possible.
When those species have diminished in the hunting area, a new prey
species is selected and hunted [32].

Some prairie falcon prey items not mentioned above include pocket
gophers (Geomyidae), cottontails and jackrabbits (Leporidae), pikas
(Ochotona spp.), wood rats (Neotoma spp.), mice, mourning doves (Zenaida
macroura), burrowing owls (Athene cunicularia), jays (Corvidae), western
meadowlarks (Sturnella neglecta), blackbirds, shrikes (Lanius spp.),
wrens (Troglodytidae), lark buntings (Calamospiza melanocorys), magpies
(Pica spp.), sparrows (Emberizidae), quail (Phasianidae), longspurs
(Calcarius spp.), pigeons (Columbidae), ducks (Anatidae), lizards,
grasshoppers, and beetles [13,27,32].


PREDATORS : 
Adult prairie falcons are seldom killed by predators, although adult
incubating birds are sometimes taken by great horned owls (Bubo
virginianus) at night [16].  Predation by coyotes (Canis latrans), dogs
(Canis familiaris), badgers (Taxidea taxus), bobcats (Lynx rufus),
golden eagles, and great horned owls is probably the greatest overall
factor in nestling mortality by predators [16,26,32].


MANAGEMENT CONSIDERATIONS : 
The current breeding status of prairie falcons is unknown.  In Utah
prairie falcons show reduced occupation rates at historical nests and
total extirpation from others.  Some western Montana populations may not
be stable, while Idaho contains an apparently stable population.  A
declining Canadian population has shown some recovery [9].

Breeding habitat loss is probably the most important factor threatening
prairie falcon populations.  Artificial aeries with reinforcing frames
should be considered for prairie falcon management where development
activities affect the availability or useability of natural aeries or
where substrate conditions reduce aerie longevity [25,31].

Alteration of prey habitat has also had an impact on prairie falcon
populations [16].  Broad expanses of grassland and prairie with
occasional scattered trees provide excellent habitat for prairie
falcons.  Unfortunately much of this habitat has been altered by
cultivation, water impoundments, or heavy grazing, which reduces the area
of suitable habitat for many prey species [20].  Range management
practices that produce or maintain ranges in good condition provide a
greater abundance and variety of prey for many raptor species including
prairie falcons [11].

Organochlorine contaminants and mercury appear to have been primarily
responsible for earlier prairie falcon declines because of direct
effects on prairie falcons and effects on their prey base.  Restrictions
on DDT and mercury use have considerably alleviated the declines caused
by biocide pollution, but populations in areas of agricultural pesticide
use continue to show lowered reproduction.  In areas where prairie
falcons feed primarily on birds, productivity and nest success are much
lower than where the diet is primarily mammalian.  In California pest
control eliminated 1 million passerines from 1966 to 1972; roughly 30
percent of these were horned larks [16].

Human disturbance near prairie falcon nest sites during the breeding
season may result in nest abandonment [16].  Construction of homes at
the base of cliffs throughout the West has caused prairie falcons to
leave areas where they may have nested for generations [11].  High
levels of human disturbance near historical nesting territories were
thought to be responsible for declines of prairie falcons in the Mojave
Desert [9].  Boyce [9] suggested placing roads at least a 15-minute walk
from a prairie falcon nest, preferably a 30-minute walk.  He also
suggests placing restrictions on recreational activites and/or closure
of habitat near nests if possible.

Prairie falcons are being bred successfully in captivity.
Captive-raised birds are being placed in wild aeries to help managers
develop techniques for reintroduction of peregrine falcons.
Captive-raised prairie falcons are also raised for falconry purposes
[16].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Falco mexicanus | Prairie Falcon