Bald Eagle
Haliaeetus leucocephalus
U.S. Fish & Wildlife Service
The bald eagle is truly an all- American
bird it ranges over most of the
continent, from the northern reaches of
Alaska and Canada down to northern
Mexico.
While our national symbol was in
danger of extinction throughout most
of its range 30 years ago, the bald eagle
has made a tremendous comeback,
its populations greatly improving in
numbers, productivity, and security in
recent years.
Juvenile bald eagles have mottled
brown and white plumage, gradually
acquiring their dark brown body and
distinctive white head and tail as they
mature. Bald eagles generally attain
adult plumage by 5 years of age. Most
are capable of breeding at 4 or 5 years
of age, but in healthy populations they
may not start breeding until much
older. Adults weigh 8 to 14 pounds
(occasionally reaching 16 pounds in
Alaska) and have wingspans of 5 ½ to
8 feet. Those in the northern range
are larger than those in the south, and
females are larger than males.
Bald eagles can live 15-25 years in the
wild, and even longer in captivity. They
typically mate for life and build huge
nests in the tops of large trees near
rivers, lakes, marshes, or other aquatic
areas. Nests are often re-used year
after year, with additions to the nests
made annually. Nests are often 4 to 6
feet wide and may weigh up to 1,000
pounds. Although bald eagles may
range over great distances, they usually
return to nest within 125 miles of where
they were raised.
Breeding bald eagles typically lay
one to three eggs once a year, which
hatch after about 35 days. The young
eagles are flying within 3 months and
are on their own about a month later.
However, disease, lack of food, bad
weather, or human interference can kill
many eaglets; recent studies show that
approximately 70% survive their first
year of life.
The staple food of most bald eagle
diets is fish, but they will also feed on
waterfowl, rabbits, snakes, turtles,
other small animals and carrion. In
winter, eagles that nest northern areas
migrate south and gather in large
numbers near open water areas where
fish and other prey are plentiful. Eagles
that nest in the south during the winter
migrate north in the summer where
food is plentiful.
Wildlife experts believe there may
have been 100,000 nesting bald eagles
in the lower 48 states when the bird
was adopted as our national symbol in
1782. Since that time, the bald eagle
has suffered from habitat destruction
and degradation, illegal shooting, and
contamination of its food source, most
notably due to the pesticide DDT. By
1963 there were only 417 bald eagle
nesting pairs in the lower 48 states.
Bald eagles have few natural enemies.
In general they prefer an environment
of quiet isolation; tall, mature trees; and
clean waters. Those conditions have
changed over much of the bald eagle’s
former habitat.
Although primarily fish and carrion
eaters, bald eagles and other raptors
were seen as marauders that killed
chickens, lambs, and other domestic
livestock. Consequently, large numbers
were shot by farmers, ranchers, and
others.
In 1940, noting that the national bird
was “threatened with extinction,”
Congress passed the Bald Eagle
Protection Act prohibiting, except
under certain specified conditions,
the taking, possession, and commerce
of bald eagles. A 1962 amendment to
this Act added the golden eagle, and
the amended law became known as
the Bald and Golden Eagle Protection
Act. In 1967, bald eagles were officially
declared an endangered species (under
a law that preceded the Endangered
Species Act of 1973) in all areas south of
the 40th parallel.
The greatest threat to the bald eagle’s
existence arose from the widespread
use of DDT and other pesticides after
World War II. DDT was used for insect
control throughout the country and
its residues washed into lakes and
streams. There, it was absorbed by
aquatic plants and animals that were
eaten by fish. The contaminated fish, in
turn, were consumed by bald eagles.
The chemical interfered with the bald
eagle’s ability to develop strong shells
for its eggs. As a result, bald eagles and
many other bird species began laying
eggs with shells so thin they often
broke during incubation or otherwise
failed to hatch. Their reproduction
disrupted, bald eagle populations
Bald eagles are fequently seen perched
on large snags above lakes or rivers.
From this vantage point they can
survey their surroundings for prey
plummeted. As the dangers of DDT
became known, in large part due to
Rachel Carson’s famous book Silent
Spring, this chemical was banned for
most uses in the U.S. in 1972.
In addition to the adverse effects of
DDT, bald eagles also died from lead
poisoning as a result of feeding on
hunter-killed or crippled waterfowl
containing lead shot and from lead shot
that was inadvertently ingested by the
waterfowl. In 1991, a 5- year program
to phase out the use of lead shot for
waterfowl hunting was completed by
the Service .
Gradually, the Service assembled
the largest colony of breeding bald
eagles in captivity at its Patuxent
Wildlife Research Center near Laurel,
Maryland, in a major effort to return
healthy eagles to the wild. The center is
now run by the U.S. Geological Survey.
Patuxent’s scientists enhanced the
species’ breeding potential by removing
the eagle’s first clutch of eggs and
incubating them artificially. The
eagles would usually then lay a second
clutch, which the birds were allowed
to incubate themselves. In all, 124 bald
eagles were hatched at Patuxent.
These captive-hatched bald eagles were
an important source for restocking
wild populations in certain areas of the
country and helped to reestablish
a broader distribution. Patuxent’s
program came to an end in 1988 as
bald eagles began to reproduce more
successfully in the wild and the center
turned its efforts toward other more
critically endangered species.
Some states, universities, and non-profit
organizations have continued
reintroduction efforts. Two methods
are generally used. Eaglets used for
reintroduction may be captive hatched
or, since usually only two young per
nest survive, they may be transferred
from a bald eagle nest with a clutch of
more than two. These “extra” eaglets
are placed in the nest of an adult pair
whose own eggs are infertile or fail to
hatch. The “foster parents” readily
adopt the chicks and raise them as their
own.
Another method, called “hacking”,
involves placing eaglets in manmade
towers at 8 weeks of age. These towers
are located in remote areas where
bald eagle populations are low or non-existent.
The eaglets are kept in an
enclosure and fed by humans who stay
out of sight. When the birds are capable
of flight, at about 12 weeks old, the
enclosure around the artificial nest is
opened and the birds are free to leave.
Food is still provided at the release
site until the birds learn to fend for
themselves in the wild.
Thanks to the banning of DDT and
these other recovery methods, bald
eagle populations have steadily
increased in the past 25 years. From
417 nesting pairs in the early 1960s,
there are now approximately 7,066 bald
eagle nesting pairs and an unknown
number of immature bald eagles in
the conterminous U.S. In the last few
years, several states have had breeding
bald eagles for the first time in years.
The bald eagle was originally listed as
endangered under the Endangered
Species Act in 43 of the lower 48 states
and listed as threatened in Michigan,
Minnesota, Oregon, Washington, and
Wisconsin. (There are about 40,000
bald eagles in Alaska and none in
Hawaii.) “Endangered” means a species
is considered in danger of extinction
throughout all or a significant portion
of its range, while “threatened”
is a less dire category, meaning a
species is considered likely to become
endangered within the foreseeable
future, but is not currently in danger of
extinction.
In July 1995, the Service announced
that bald eagles in the lower 48
states had recovered to the point
that those populations that were
previously considered endangered
were now considered threatened.
The Service then formally upgraded
those populations from endangered to
threatened.
In July 1999, the Fish and Wildlife
Service proposed to remove the bald
eagle from the list of threatened and
endangered species. Since then, the
Service has reviewed the comments
received on that proposal along with
new data and information to determine
the best ways to manage for the species
once it is removed from the protections
of the Endangered Species Act. In
2006, the Fish and Wildlife Service
re-opened the public comment period
due to new information on the proposal
to delist. Data gathered during this
comment period will be factored into
a final decision on the status of the
species.
U.S. Fish & Wildlife Service
http://www.fws.gov
February 2006
Bald eagles normally lay two to three
eggs a year, which hatch after about
35 days. The eagles learn to fly within
three months and are on their own
about a month later.
As a recovery method, biologists place
eagles into the nest of adult pairs whose
own eggs failed to hatch. The pair then
serve as “foster parents.”
