BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Buteo regalis | Ferruginous Hawk 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - Most ferruginous hawks become sexually mature
at 2 years of age [5].

Breeding season - The ferruginous hawk generally returns to breeding
grounds in late March or early April [24] and begin nest construction in
April [5].  Breeding pairs aggressively defend their nesting territory.
Nests are frequently reused by the same pair in subsequent years [24].

Clutch size and incubation - The ferruginous hawk generally lays three
to four eggs in April but this number varies with fluctuating food
supply.  The eggs are incubated for 28 to 36 days [5,21].  Incubation is
shared by both sexes [5,21].  The ferruginous hawk generally will not
lay a replacement clutch or renest if disturbed [21].

Fledging - Male nestlings fledge at 38 to 40 days.  The females, which
are heavier and develop more slowly, fledge about 10 days later [21].

Fall migration - Migration generally begins in late September through
early October, with the onset of cold weather [21].

Spring migration - Ferruginous hawks usually arrive in the northern tier
of states from late March through early April.  The yearling ferruginous
hawks arrive in May through early June [21].

Longevity - The maximum potential longevity for the ferruginous hawk is
about 20 years [21].


PREFERRED HABITAT : 
The ferruginous hawk inhabits semiarid to arid western plains and
intermountain regions [6].  It occupies open country with scattered
trees, primarily prairies, plains, and badlands [1,6].  The ferruginous
hawk avoids high elevations, forest interiors, steep, narrow canyons, and
high cliffs [12,21].

Nesting habitat - Ferruginous hawk nesting habitat consists of
communities with isolated trees, woodland edges, buttes, cliffs, and/or
grassland with some relief.  Ferruginous hawks generally nest within a
short distance of their food supply [11].  Most ferruginous hawk nesting
studies report a preference for tree nests [16,20,27].  However,
ferruginous hawks will use a wide variety of sites, including riverbed
mounds, cutbanks, small hills, small cliffs, powerline structures, and
haystacks [6].

Tree nests are usually in the upper canopy, from 6 to 55 feet (2-17 m)
above the ground [6].  The nest tree is typically isolated or is in an
isolated small cluster of trees in an exposed location.  Juniper is the
most commonly used tree for nesting, but pine (Pinus spp.), willow
(Salix spp.), cottonwood (Populus spp.), swamp oak (Quercus spp.), and
sagebrush have been used [16,21].  In northern Utah and southeastern
Idaho, Howard and Wolfe [10] reported that Utah juniper (Juniperus
osteosperma) provided sites for 95 percent of the observed ferruginous
hawk nests.  Desert shrub types and Fairway wheatgrass (Agropyron
cristatum)-seeded areas comprised the dominant vegetation around nest
sites [10].  Of the active ferruginous hawk nests in the Centennial
Valley of the Greater Yellowstone Ecosystem, 70 percent were in willows
along streams [5].  Ferruginous hawks will nest in trees and large
shrubs along the edge of forests and wooded areas that are adjacent to
open areas [11].

Ground nests tend to be on slopes, knolls, and crests of ridges, often
on or lodged between boulders [21].  The ferruginous hawk will accept
both modified and completely artifical nest structures.  Use of
artifical structures for nesting appears to occur most often when
natural nesting substrates are scarce or unavailable [11].

Of 71 ferruginous hawk nests on the plains of Colorado, 69 percent were
in trees, 11.3 percent on erosional remnants, 5.6 percent on the ground,
5.6 percent on cliffs, 5.6 percent on creekbanks, and 2.9 percent on
artifical structures [20].  Ground nests in southern Idaho were
constructed in areas of rangeland where no suitable nest trees were
available.  They were usually located near a small hill [11].  In
Campbell and Converse counties, Wyoming, the majority of ferruginous
hawk nests were built on the ground, usually on a fairly prominent rock,
eroded creekbank, or sandstone or scoria outcrop.  Ground nests were
often built in new locations in successive years [22].

Foraging habitat - The ferruginous hawk generally forages in open
habitats with short vegetation containing abundant prey [11,12].  The
best habitat is occupied by high quality prey on over 75 percent of the
home range.  This estimate is based on data that indicate that
ferruginous hawks generally hunt over large portions of their home
range.  High quality food is not required over 100 percent of the area
because the effective hunting range is usually smaller than the home
range.  Food suitability for the ferruginous hawk is optimum when the
vegetation occurs at a mix of heights and densities which optimizes prey
abundance and minimizes hunting interference [11].  The ferruginous hawk
hunts mainly in early morning and late afternoon from low flights and
perches [5].

Winter habitat - The ferruginous hawk inhabits open terrain from
grasslands to deserts during migration and winter.  It is the most
common wintering buteo on wide expanses of treeless terrain [21].


COVER REQUIREMENTS : 
Wooded foothills interspersed with valleys and large desert expanses
provide optimal nesting sites for the ferruginous hawk because of the
combination of human inaccessibility and ease of surveillance of the
surrounding area.  Tree nests are often exposed, providing protection
from ground predators and shade for nestlings [11].  Ground nests are
concealed.  In South Dakota, ground nests were always located in
prairies with tall herbaceous cover or prairies that were in a lightly
grazed condition [16].  On the plains of Colorado, ferruginous hawks
used fenceposts, telephone poles, and dead trees as perch sites [11].


FOOD HABITS : 
The ferruginous hawk feeds primarily on rabbits (Lepus spp. and
Sylvilagus spp.), ground squirrels (Spermophilus spp.), and prairie dogs
(Cynomys spp.), but also takes mice, rats, gophers, birds, snakes,
locusts, and crickets [6,11,21].  Analysis of prey items collected from
nests indicate that jackrabbits (Lepus spp.) often constitute the most
important prey item based on biomass [10,23,27,31,33].  A central Utah
study reported that black-tailed jackrabbits (Lepus californicus) made
up more than 95 percent of ferruginous hawk prey biomass [33].

Significant fluctuations in ferruginous hawk densities may be an
indication of the abundance and diversity of prey species.  A decline in
ferruginous hawk numbers in Utah was directly correlated with a drop in
the jackrabbit population [11].  Ferruginous hawk fledgling success and
nesting densities in southern Idaho and northern Utah were closely
correlated with the cyclic black-tailed jackrabbit population [28].
However, in years of low prey abundance, ferruginous hawks will often
switch from primary to alternate prey [21,32].  The nesting success of
some populations of ferruginous hawks in Utah, where jackrabbit numbers
declined dramatically, was attributed to the presence of a broad prey
base [32].


PREDATORS : 
Golden eagles (Aquila chrysaetos), prairie falcons (Falco mexicanus),
great horned owls (Bubo virginianus), coyotes (Canis latrans) and red
foxes (Vulpes vulpes) are predators of ferruginous hawk eggs and
nestlings [29].


MANAGEMENT CONSIDERATIONS : 
The ferruginous hawk requires large tracts of relatively undisturbed
areas [5].  The conversion of extensive tracts of native vegetation into
monotypic stands for grazing and agriculture may reduce ferruginous hawk
densities and reproductive success.  Reductions may be due to decreased
availability of major prey, loss of nest sites, and increased human
disturbance [3,10,11].

The ferruginous hawk is vulnerable to tree removal.  Peripheral trees
should be left during tree removal and chaining operations to provide
nest sites.  Isolated trees can be protected by fenced enclosures.  Loss
of isolated trees can be remediated by artifical nest structures [11].

Maximum consideration should be afforded this species when range
development is planned [3].  Land management practices that dramatically
alter the density and structure of native vegetation can adversely
affect both jackrabbit and alternate prey populations, resulting in a
reduction in breeding ferruginous hawks.  Range management practices
that support abundant and diverse prey may provide suitable food
alternatives for the ferruginous hawk during periods of jackrabbit
decline [11].

Conversion of extensive tracts of brushland and native vegetation to
either agriculture or monotypic fields of grass is particularly
disruptive to jackrabbits and cottontails [11,33].  Areas providing an
interspersion of tall cover and open spaces are preferred by
jackrabbits.  Moderate amounts of rangeland and agricultural land
support pocket gophers and ground squirrels, which may provide alternate
prey species for the ferruginous hawk [11].  Although overgrazed areas
may temporarily provide vulnerable prey, it is unlikely that such areas
will support an adequate prey base for any length of time [11].
Additionally, severe overgrazing could affect ferruginous hawk nest site
selection by causing a decline in the regeneration of willows [5].


Vegetation management for the ferruginous hawk should emphasize
maximizing the amount of edge and interspersion of shrublands and
grasslands.  Where Fairway wheatgrass plantings are planned, a minimum
of 20 percent of the area should be left in scattered islands of shrubby
vegetation.  This design can produce optimum habitat for the ferruginous
hawk within 3 or 4 years after treatment [10].

The ferruginous hawk is very sensitive to human disturbance during the
nesting season and may abandon a nest during the pre-egg laying period
and incubation even if it is disturbed only once [5,11].  It is
important to time the implementation of range improvement activities to
avoid nesting periods.  Late summer and fall are the optimum seasons for
range improvement practices in areas containing nests [3].  It is also
important to avoid range improvement activities in areas of high
ferruginous hawk foraging use [3,10].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Buteo regalis | Ferruginous Hawk