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Distribution
and Migration of Bald Eagles
 Past & Present Range
In the mid-1600s when the first white settlers landed on the
shores of North America bald eagles ranged over most of the
continent. Bald eagle populations were estimated upward to 500,000
birds. In what later became the 50 United States, 46 had nesting
populations of bald eagles.
Alaska has had historically high populations of eagles. In the
1920s it was reported that bald eagles were as common as ravens
along the southeastern Alaska coast.
As late as the 1800s, nests on the Chesapeake Bay averaged one per
mile. It was claimed at this time to have as many as 12,000 in the
bay area. The eagles could be seen in abundance on Manhattan
Island and the Hudson River. In the mid 1800s eagles were commonly
reported around hog slaughter operations in Keokuk, Iowa.
As white settlers moved west eagle populations declined. Much of
this decline was due to hunting, disturbance and habitat
destruction. The bald eagle was forced into isolated regional
pockets of the United States, Canada and Alaska. Their numbers
have rebounded greatly from the 1960s when DDT nearly wiped them
out, but still they inhabit only these regional areas. In order
bald eagles are most numerous in Alaska, Wisconsin, Minnesota,
Florida, Oregon and Washington. A number of states have begun
reintroduction programs – Tennessee, New York and Georgia are
just a few of these.
The 1995 estimate was 4,712 pairs in the lower 48 states.
Migration
Juvenile eagles hatched in the north will migrate south in
October, but may wander a great deal along the way. Northern adult
eagles begin their fall migration about the time that their
northern nesting lakes begin to freeze, usually in mid-November.
The young of southern nests will migrate north after fledging and
summers after until they pair and establish territories of their
own in the south. After they have chosen those southern
territories they will remain there year round.
They typically begin their fall migration by leaving their roost
sites and utilizing the thermals that form during the day. They
may fly on their migration route until as late as 6:00 p.m., but
seldom fly after dark. They will usually stop before 6:00 p.m.,
locate a food source loaf and roost until the next morning when
they will resume their migration flight. Eagles choose to migrate
with tailwinds and thermals to help conserve energy.
Spring migration occurs in a
much shorter time span. Some theories suggest that it is due to
the scarcity of food as the eagles move back north over
ice-covered lakes and rivers. Others suggest it is the rush to
arrive at the nesting territories. Males typically will leave the
wintering area first, females shortly after and juveniles last.
Eagles will also fly in what seems to be synchronized patterns
through the air, called “roller coastering”. There are times
that eagles will play with sticks during courtship – exchanging
sticks in mid-air or dropping the stick so the other will retrieve
it. Researchers believe that these flights exhibit territorial
behavior or are statements of dominance.
With the perfect conditions
they can average anywhere from 90 to 270 miles in a day with an
average flight speed of 30 m.p.h. If thermals fail to form the
eagles will find areas to loaf and roost until the right
conditions present themselves.
Paired males will typically leave their wintering area for the
nesting territory before the female, so the serious courting
usually takes place near the nest site rather than at their
wintering location. Either the male or the female may initiate
copulation and typically copulation occurs in the six days before
the first egg is laid and continues until the last egg is laid.
Eagles will copulate throughout the summer and into fall, but
typically do not produce young, rather this may reinforce the pair
bond.
For eagles nesting here along the open stretches of the river,
nesting and egg-laying can occur as early as mid-February. As long
as there is a source of food to feed themselves and their young,
the eagle is safe in beginning its mating ritual. For those pairs
nesting on northern lakes the egg laying may not occur until as
late as April. |
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