Eagles are the largest
bird of prey in North America. When hatched, eaglets
have thick, light-colored down that is replaced with
dark feathers within 5 to 6 weeks. Eagles have long
sharp talons by which they capture and kill prey
animals. The tarsi (lower legs) are feathered to the
toes on golden eagles but are bare on bald eagles (Fig.
Golden eagles weigh from 7
to 13 pounds (3 to 6 kg) as adults and have a wingspread
of 6 to 7 1/2 feet (1.8 to 2.3 m); females are about
one-third larger than males.
The plumage color of
golden eagles changes with age. Birds in their first
year are predominantly dark brown, with considerable
areas of white on the underside of their wing flight
feathers. The tail has a broad white band with a dark
terminal band at the tip. The back of the neck may or
may not appear gold or bronze, depending upon light
conditions and the individual bird. This color is what
gave the golden eagle its common name. Adult eagles are
dark brown or bronze (Figs. 2 and 3).
Bald eagles weigh from 9
to 15 pounds (4 to 7 kg) as adults and have a wingspread
of 7 to 8 feet (2.1 to 2.4 m). As in golden eagles,
females are about one-third larger than males.
Bald eagle plumage color
also changes with age. Juvenile bald eagles generally
are mottled brown or nearly black and resemble adult
golden eagles. These juveniles have no distinct white
patches. Their tail and wings are mottled brown and
white on the underside in contrast to the characteristic
white patches under the wings and the white-banded tail
of juvenile golden eagles. Although adult bald eagles of
both sexes have the white head and tail, they do not
develop these characteristics until they are 4 to 5
years of age or older (Figs. 2 and 3).
Fig. 2. Characteristics of
golden and bald eagles. Fig. 3. Golden and bald eagles
in flight. Immature golden eagle and bald eagle
Golden eagles in North
America occur in greatest numbers from Alaska southward
throughout the mountain and intermountain regions of the
West and into Mexico. They occur in lower numbers to the
east across Canada, the Great Lakes states, and the
Appalachian Mountains of the eastern United States.
Bald eagles have a similar
range but tend to be most common near the seacoasts and
other large bodies of water. In winter they may
concentrate along major lakes and rivers. By far the
greatest concentration of bald eagles is in Alaska,
along large rivers and the coast.
Eagles frequent a wide
variety of habitats. Golden eagles seem to prefer the
rough broken terrain of foothills and mountains,
valleys, rimrocks, and escarpments. They commonly hunt
the adjacent plains for food.
Bald eagles seem to prefer
timbered areas along coasts, large lakes, and rivers,
but they also occupy other areas.
Eagles often abandon
habitat that is subject to intensive human activity and
move to more remote areas.
Although regional and
seasonal differences in food habits exist, golden eagle
prey consists mostly of small mammals such as
jackrabbits, cottontails, prairie dogs, and ground
squirrels. A variety of birds and reptiles also have
been recorded as prey. Nesting pairs or concentrations
of juvenile birds can be a major cause of predation on
local game bird populations. Golden eagles also readily
Golden eagles sometimes
attack large mammals; deer and pronghorns of all ages
have been observed being attacked or killed by eagles.
Records also exist of bighorn sheep, coyotes, bobcats,
and foxes being killed. Occasionally, golden eagles kill
calves, sheep, or goats. However, attacks on animals
that weigh more than 30 to 40 pounds (14 to 18 kg) are
uncommon. Where golden eagles prey on domestic animals,
they usually take lambs and kids, but some become
persistent predators of domestic livestock as large as
500 pounds (227 kg).
Bald eagles rely heavily
on fish and carrion where available. They readily adapt,
however, to preying on waterfowl, other birds, rabbits,
and other small mammals. They also occasionally kill
adult deer, pronghorns, and calves. At times, some may
prey repeatedly on domestic sheep and goats, primarily
young lambs and kids.
Experiments with captive
eagles indicate that adults require about 3/4 pound (1/3
kg) of meat per day to maintain their weight; young,
growing eagles require much more food. Accounts of the
weight that an eagle can carry in flight often have been
misstated. Experiments indicate that without wind to
assist them even large eagles cannot take off from flat
ground with more than 5 or 6 pounds (2 to 3 kg) in their
talons. Eagles flying into the wind and taking prey from
hillsides, however, sometimes carry animals of twice
those weights for considerable distances.
Biology, Reproduction, and Behavior Nesting Behavior
Eagle courtship displays
consist of a series of “roller coaster” dives and other
aerial maneuvers. These characteristic maneuvers may be
seen nearly any time of the year, but are most common
just before and during the late winter breeding season.
Aerial displays made during other seasons may serve to
identify territorial boundaries and maintain pair bonds
Eagle nests of sticks and
twigs are built either on cliffs or in trees. Nests can
be very large, sometimes up to 8 feet (2.4 m) wide and
deep. The same nests may be used several years, becoming
larger as new material is added each year. Eagles
usually have several nests in a vicinity and may use
Nesting can begin as early
as February in the south and as late as June in the
north. At nesting time, an adult pair builds new nests
or repairs old ones. Often, a single pair will build or
repair two or three nests during a single season. These
alternate nests are legally defined as “active” and are
protected by law. The nesting territory of golden eagles
varies from about 3 to 65 square miles (8 to 168 km2)
Bald eagles seem less
antagonistic to other nesting pairs, and their nesting
territories, typically near water, may be much smaller.
Studies in Alaska have shown that bald eagle nests may
be spaced as closely as 1/4 mile (0.4 km) apart along
rivers, with nesting territories as small as 30 to 40
acres (12 to 16 ha) in some cases. This may be due to
more plentiful food near water.
Usually, 2 (1 to 3) white
or mottled brownish eggs are laid after nesting behavior
begins. The eggs hatch after a 35- to 45-day incubation
period. Both adults hunt and secure food for the young,
with the female doing most of the incubating, feeding,
and brooding. Young eagles become strong enough to tear
meat apart by 50 days of age. They are fully feathered
and ready to leave the nest 65 to 70 days after
hatching. Although the young are as large as the adult
birds at this time, their parents may continue to
provide them with food and protection for as long as 3
months after they leave the nest.
Not all eagle eggs hatch,
and the death rate of young eagles, as in other birds of
prey, is high. Young eagles are antagonistic toward each
other and the stronger often kills or causes the weaker
to die of starvation. Losses due to exposure, diseases,
parasites, and predation occur while the young are still
in the nest. Up to 75% of the young eagles die during
their first year due to starvation, disease, and causes
directly or indirectly associated with humans.
chemicals, trapping, and power line electrocutions
account for a large number of eagle fatalities. Injuries
resulting from accidents such as flying into power lines
or being hit by vehicles while feeding on road-killed
animals also occur.
Dispersal and Migration
Juvenile golden eagles
leave the nesting territory as early as May in the
Southwest and as late as October or November in the
North. Many of the golden eagles that breed in the
northern United States and Canada migrate south for the
winter. They arrive in the southwestern United States as
early as October and reach peak numbers in December and
January in Texas and February and March in New Mexico
before migrating back north. Only resident birds remain
by late May. Golden eagles breeding in the more
temperate climates south of Canada often remain in the
same region year-round. Many northern golden eagles
migrate through areas occupied by resident eagles to
areas farther south.
Bald eagles usually are
found in coastal areas, along lakes and rivers, and on
mountain ridges. Usually, they are seen soaring or
sitting on commanding snags along bluffs or shores.
Pairs sometimes are observed together. After the nesting
season, they may congregate in areas where food is more
readily available, and then large numbers may roost in
the same tree. Immature birds also may roost together
during the winter.
Bald eagles will winter as
far north as open water and food are available,
migrating out of more northerly nesting areas. Returns
from banded bald eagles indicate that birds that nest in
Florida often migrate to the northeastern states and
southern Canada in midsummer and return in early fall.
Returns from birds banded in Saskatchewan indicate that
some move as far south as Texas and Arizona.
Research indicates that
golden eagles are maintaining static populations in
areas undisturbed by humans. The wintering population
south of Canada is estimated at 63,000 birds. Aerial
surveys conducted by the USFWS in 12 western states show
average densities of about 10 golden eagles per 100
square miles (4/100 km2) in midwinter study areas.
Golden eagles also winter in parts of Alaska, Canada,
and Mexico; however, the number in this latter group
would not likely exceed 10,000 birds.
Current population survey
information indicates a sizable and healthy population
of golden eagles in the western states. The current
breeding population for 17 western states is estimated
at 17,000 to 20,000 breeding pairs. Information
indicates a slight decline in the western population as
a whole, with drastic declines in some specific areas
associated with increased human activity.
Bald eagles occur across
the continent from northern Alaska to Newfoundland, and
south to southern Florida and Baja California. They are
found on Bering Island and the Aleutian Islands. Two
subspecies are recognized: the southern bald eagle (H.
l. leucocephalus) and the northern bald eagle (H. l.
alascans). The primary difference in appearance is size,
the northern race being larger and heavier. There is a
gradual increase in size from south to north.
The northern bald eagle
population in Alaska is estimated at 35,000 to 40,000.
In 1989, the breeding population of bald eagles in the
continental United States (excluding Alaska) was
estimated to be about 2,673 pairs. This estimate
included both races. The nationwide January eagle count
sponsored by the National Audubon Society indicated
about 3,700 birds each year from 1961 through 1966. The
annual midwinter counts coordinated by the National
Wildlife Federation since 1979 have ranged from about
9,000 birds to more than 13,000 in the contiguous 48
states. In 1989, 11,610 bald eagles were counted in key
wintering areas. The 1989 count does not represent a
comprehensive national count, so it is not directly
comparable to earlier counts. These January counts
indicated four areas of greatest abundance nationwide:
the upper half of the Mississippi Valley, the Northwest
(Washington, Oregon, Idaho, and Montana), Florida, and
the Chesapeake Bay area.
Damage and Damage Identification
Golden eagles are more
likely to prey on livestock than are bald eagles. Both
species readily feed on livestock carrion and carcasses
left by foxes and coyotes, although some individuals
prefer live prey to carrion. Eagles are efficient
predators and can cause severe losses of young
livestock, particularly where concentrations of eagles
exist. Generally, they prey on young animals, primarily
lambs and kids, although they are capable of killing
adults. Eagles also take young deer and pronghorns, as
well as some adults.
Eagles have three front
toes opposing the hind toe, or hallux, on each foot. The
front talons normally leave wounds 1 to 3 inches (2.5 to
7.5 cm) apart, with the wound from the hallux 4 to 6
inches (10-15 cm) from the wound made by the middle
front talon. On animals the size of small lambs and
kids, fewer than four talon wounds may be found, one
made by the hallux and one or two by the opposing
talons. Talon punctures typically are deeper than those
caused by canine teeth and somewhat triangular or
oblong. Crushing between the wounds usually is not
found, although compression fractures of the skulls of
small animals may occur from an eagle’s grip. Bruises
from their grip are relatively common.
Eagles seize small lambs
and kids anywhere on the head, neck, or body, frequently
grasping from the front or side. They usually kill adult
animals, or lambs and kids weighing 25 pounds (11 kg) or
more, by multiple talon stabs into the upper ribs and
back. Their feet and talons are well adapted to closing
around the backbone, with the talons puncturing large
internal arteries, frequently the aorta in front of the
kidneys. The major cause of death is shock produced by
massive internal hemorrhage from punctured arteries or
collapse of the lungs when the rib cage is punctured.
Eagles also may simply seize young lambs, kids, or fawns
and begin feeding, causing the prey to die from shock
and loss of blood as it is eviscerated.
Eagles skin out carcasses,
turning the hide inside out while leaving much of the
skeleton intact, with the lower legs and skull still
joined to the hide. On very young animals, however, the
ribs often are neatly clipped off close to the backbone
and eaten. Eagles frequently do not eat the breast bone,
but some clip off and eat the lower jaw, nose, and ears.
Quite often, they remove the palate and floor pan of the
skull and eat the brain. They may clean all major
hemorrhages off the skin, leaving very little evidence
of the cause of death, even though there may be many
talon punctures in the skin. Ears, tendons, and other
tissues are sheared off cleanly by the eagle’s beak.
Larger carcasses heavily
fed on by eagles may have the skin turned inside out
with the skull, backbone, ribs, and leg bones left
intact, but with nearly all flesh and viscera missing.
The rumen normally is not eaten. Eagles may defecate
around a carcass, leaving characteristic white streaks
of feces on the soil. Their tracks may be visible in
soft or dusty soil. Small downy feathers often are
evident on vegetation where eagles have fed.
Both bald and golden
eagles and their nests and nest sites are protected by
the federal Bald Eagle Protection Act and state
regulations. In June 1940, legislation was passed that
outlawed killing, possessing, selling, or trading any
live or dead bald eagle, or any part of a bald eagle,
including feathers, eggs, and nests. In 1962, the same
protection was afforded the golden eagle. Provisions in
these laws allow specific permits to be issued by the US
Department of Interior for the taking of eagles or their
parts for scientific research, for exhibitions and
Indian religious purposes, and for control of predation
to domestic livestock (50 CFR, Part 22). Permits for
control of eagles to prevent or reduce predation on
livestock, however, have not been issued by the US
Department of Interior since 1970. Also, regulations
promulgated by the Secretary of Interior under authority
of the Endangered Species Act of 1973 (as amended)
prohibit “taking” of an endangered species, such as bald
eagles. Because golden eagles also are protected, they
too cannot be “taken.” Congress has defined the term
take as follows: “to harass, harm, pursue, hunt, shoot,
wound, kill, trap, capture, or collect, or to attempt to
engage in any such conduct.”
A depredation permit from
the US Department of Interior is required to carry out
any eagle damage control activities. This requires a
formal consultation and biological assessment under
Section 7 of the Endangered Species Act for bald eagles.
At present, permits to take, harass, or scare
depredating golden eagles are issued routinely to the
western Regional Director of the USDA-APHIS-ADC by the
USFWS. Only USDA-APHIS-ADC personnel are permitted to
engage in eagle damage control activity under such
Damage Prevention and Control Methods
Eagles rarely attack livestock around buildings or
pens. Therefore, livestock confined in buildings or pens
of 1 to 2 acres (1/2 to 1 ha) usually are safe from
eagles. Fences, however, are no constraint to eagles;
livestock must be protected by other means.
Cultural Methods and
A common practice for many sheep and goat producers
is to avoid use of pastures where predation is severe
until lambs and kids are several weeks old. This
practice may reduce exposure of individual flocks or
herds to predation, but it is not always effective. It
may, however, cause predators to shift their attention
to livestock owned by other operators.
Eagles prefer relatively
open areas in which to take their prey. Lambs and kids
are much less vulnerable to eagle predation in brushy
and wooded areas. While use of such pastures may not
completely prevent eagle predation, it may help to
protect lambs and kids up to 4 to 6 weeks of age.
Predation by eagles is seldom a problem after lambs and
kids have reached 6 weeks of age.
Herding of livestock,
where feasible, usually will reduce eagle predation
because humans tend to frighten eagles. Herding may be
only partially effective, however, because eagles, like
other predators, adapt to existing conditions.
Shifting the lambing and
kidding seasons to an earlier or later period may also
help to reduce or prevent eagle predation, but the
decision must be based on the availability of pasture,
plant phenology, season and weather, availability of
labor, marketing constraints, and other considerations.
In some areas, such a shift may cause increased exposure
of young livestock to other predator species.
Shed lambing and kidding
is effective in preventing eagle predation during the
confinement period. Its limitations include the
availability of space, the quality and costs of feed
necessary to ensure and maintain milk production for
lambs and kids, and the length of confinement. Unless
the young are confined up to a month or more, shed
lambing and kidding will provide protection when the
chance of eagle predation is lowest. Eagles generally
take older lambs or kids that are running and playing
some distance from flocks, not the younger ones, who
usually stay close to their mother and within the flock.
Predation is most severe on young that are at least 2 to
4 weeks of age. Confinement of sheep and goats also may
be a very costly management decision for forage
utilization where high quality forage is available in
pastures and weather does not present a constraint to
the use of that forage.
Carrion removal may help
limit the size of local eagle populations. Eliminating
the eagles’ food source may force a potential problem to
move elsewhere. It may, however, encourage the eagles to
kill lambs or kids. If eagles depend heavily on carrion
in an area where young livestock are to be protected,
the eagles must either have an alternate food source or
be persuaded to move.
Little information is available on the effects of
guard dogs to prevent eagle predation. Some dogs,
breeds other than guard dogs, will chase birds. They
would probably be more effective in protecting sheep or
goats in small pastures than in large pastures and open
range conditions, particularly where livestock are
spread over large areas.
Sonic devices have been
tested and show little benefit in preventing or reducing
Scarecrows, made from 2 x
4-inch (5 x 10-cm) lumber and chicken wire (Fig. 4) and
dressed in pants or skirts, shirts, and hats, may keep
eagles away from an area for up to 3 weeks. The chicken
wire bodies allow the arms to wave in the wind. Clothes
can be purchased secondhand from Goodwill Industries for
about $3.50 per scarecrow. The frame is made of standard
grade lumber at a cost of about $6.50 per scarecrow; a
lesser grade or scrap lumber should reduce the cost.
Almost anything can be used as a stand, including 2 x 4s
or existing fence posts. The chicken wire is attached to
the 2 x 4s with a staple gun, which also comes in handy
for making field repairs. Building time is about 1/2
hour. Fluorescent orange paint can be sprayed on the
backs and chests of scarecrows and their arms hung with
shiny pans to increase visibility. Erect scarecrows on a
high ridge or point, where sheep and goats usually bed.
Most eagle predation occurs about sunup so the lambs or
kids will be close to the scarecrows during the time of
greatest danger. When eagles start to habituate to
scarecrows, harass them by shooting cracker shells near
perched or low-flying eagles. This activity will
reinforce the fear associated with humans and
scarecrows. A permit is required for such harassment. In
areas where ravens are common and preying on lambs or
kids, shooting or shooting at ravens keeps eagles wary
of scarecrows; again, a permit is required for this
repellents are registered or effective in reducing eagle
toxicants are registered or permitted for use in
preventing or controlling eagle predation.
Trapping, Snaring, and
Trapping, snaring, or shooting eagles is illegal,
except by permit. Regulations permit the Director, USFWS,
to issue permits for removal of depredating eagles
“under permit by firearms, traps, or other suitable
means except by poison or from aircraft.” However, by
policy of the Secretary, US Department of Interior, such
permits are not issued. The sole exception is very
limited live-trapping or net-gunning from a helicopter
and transplanting of eagles by USFWS and USDA-APHIS-ADC
personnel. Livestock owners who have, or suspect that
they have, eagle depredation should contact the USFWS or
USDA-APHIS-ADC for assistance and evaluation. Live
trapping and removal of depredating eagles by the USFWS
is permitted under certain conditions, and a limited
amount of such control is carried out. Net gunning from
a helicopter allows quick and selective removal of
depredating eagles from an area.
Economics of Damage and Control
Although eagles may
benefit producers by preying on rodents and rabbits and
feeding on carrion, they may have a major adverse impact
on individual producers by preying on young lambs, kids,
exotic game species, and other game animals. Losses are
most severe where nesting eagles prey repeatedly on the
same flock or where migrant eagles concentrate in an
area and cause major losses over a short period of time.
Whether eagle damage
control is necessary and beneficial depends on the
levels of loss, the costs of control, and the
effectiveness of control efforts for each damage
situation. The severe restrictions on the application of
any type of eagle control and the long delays in
securing the necessary permits and/or assistance from
the US Department of Interior are major constraints to
the protection of livestock.
Reviews and suggestions by
D. L. Flath, D. W. Hawthorne, G. L. Nunley, M. J. Shult,
C. W. Ramsey, W. Rightmire, and R. M. Timm were of major
help in the preparation of this manuscript.
Figure 1, bald eagle, from
Charles W. Schartz, Wildlife — Drawings, 1980, Missouri
Department of Conservation, Jefferson City, p. 53,
adapted by Emily Oseas Routman; golden eagle by Emily
Figures 2 and 3 by Emily
Oseas Routman, adapted from Susan Brooke in US Fish and
Wildlife Service and Texas Agricultural Extension
Service (no date), and from Grossman. M.L. and J. Hamlet
(1964), Birds of Prey of the World, C.N. Potter, New
York, 496 pp.
Figure 4 by Daniel B. Pond
(1984), Montana Cooperative Wildlife Research Unit,
University of Montana, Missoula.
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Scott E. Hygnstrom; Robert
M. Timm; Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control Great Plains Agricultural
Council Wildlife Committee