HABITAT AND RANGE:
Bald Eagles live along shores of lakes
and rivers. They are native only to
North America, except for a few in
eastern Siberia. The extent of their
range has decreased during the 20th
century, but it is slowly increasing due
to extensive hacking programs and the
banning of highly persistent pesticides.
PHYSICAL CHARACTERISTICS:
Like most birds of prey, the female is
larger than the male, and she is usually
around 42” high, has a 7-8 foot
wingspan, and weighs 10-14 pounds. The
male is usually about 35” high, has a 6
˝ -7 foot wingspan, and weighs 8-10
pounds. It is interesting to note that
the young are often larger and heavier
than either of the parents. Apparently,
as the eagle matures, its bones contract
slightly, and it loses weight, since as
a flying adult, it exercises more. A
bald eagle has more than 7,000 feathers,
but all of them together weigh less than
21 ounces. In fact, 30 feathers way
weigh less than a penny! Being light
weight is very important for flight. The
entire skeletal system of an eagle is
just slightly more than one half pound;
the 8 foot long wings weigh less than 2
pounds. Although a bald eagle looks big,
it usually weighs 2 pounds less than the
average house cat.
ADAPTATIONS:
Bald eagles are diurnal predators. They
are non-migratory except when winter is
severe enough to freeze over the water
sources upon which they rely on for
food.
DIET: The
Bald eagle’s diet consists primarily of
fish (60-90%). Eagles are remarkable
predators. While soaring at 500 feet, an
eagle can spot a fish a mile away, and
then swoop down on it at 100 mph. After
swinging its talons forward, it plucks
up the fish and seeks a perch from which
to feed. Eagles will also eat dead fish
and are not above stealing fish from
osprey. Other food includes carrion,
rabbits, turtles, waterfowl and other
small birds, small rodents, and crabs.
They eat only 5-10% of their body weight
a day (about a pound of food). Captive
eagles may be fed fish, chicks, mice,
rats, or a commercially prepared Bird of
Prey diet (BOP). In order to ensure a
complete diet, these food items are
alternated.
REPRODUCTION AND DEVELOPMENT:
Nesting is often preceded by an
aerial courtship display. Locking
talons, the pair dives and somersaults
across the sky. Bald eagles mate for
life, and both help to build the nest
(aerie, or eyrie). The aerie site is
usually 50-100 feet off the ground in a
large tree situated near water. The
completed nest, 5 feet across and 41/2
feet deep, may take four days to build.
Often eagles will return to the same
nest year after year, and add about a
foot of new twigs and branches. One of
the largest nests ever observed was in
St. Petersburg, FL; occupied for at
least 35 consecutive years, it was 20
feet deep, 91/2 feet in diameter, and
weighed 2 tons! Although it may appear
that the birds purposefully choose to
nest among dead branches, such is not
the case. Oils from fish that have been
brought to the nest seep through the
bark and stop the upward flow of sap,
eventually killing the branch. The
female lays only 2 eggs each season
(usually March or April in this area).
The eggs, unmarked and dull white, are
actually quite small for such a large
bird; it is only about an inch longer
and wider than a chicken egg. After 35
days, the eggs begin to hatch, taking
about 18 hours for the eaglet to cut its
way out. Since the parents begin to
incubate the eggs as soon as the first
is laid, the young hatch a few days
apart. Often, the youngest will not get
enough food to survive; thus, these
birds are typically the ones removed for
captive raising and future release
programs (“hacking”). The downy white
chicks develop drab brownish-black
juvenile feathers in 3-4 weeks. By the
time the birds are 6-7 weeks old, they
are able to walk around the nest, but
will be 3 months old before they begin
to fly. Unlike most birds, the eaglets
often return to the nest after their
maiden flight; sometimes the parents
will continue to feed them there.
However, when fall approaches, the young
birds are on their own. At the end of
the first year the white head and tail
feathers that characterize the adults
begin to appear, but will not be
completely in place until the bird is
4-5 years old, and sexually mature. Bald
eagles can live for 35-45 years.
