Bald eagles, our national emblem, are one of two species of
eagles found in the United States. Their breeding range extends
from Alaska and Newfoundland south to Baja California and Florida,
although many areas in the interior of the continent have few, if
any nesting pairs. As adults, eagles have a chocolate brown body
and wings, with their trademark white heads and tail feathers.
They also boast a long bright yellow beak with a hooked tip and
two inch gray talons protruding from their feather-less toes. At
up to 16 pounds (average 12), they have wing spans of six and one
half to eight feet. Adult females are much larger than males,
averaging 34 to 43 inches in length, while males are only 30 to 35
inches in length. Immature eagles are almost completely brown with
irregular patches of white under their wings and tail.
Nests are usually constructed near seacoasts, lakes or large
rivers to be near their most common food supply: fish. Although
they are quite capable of catching their own, sometimes even
wading in shallow water to stalk fish like herons, they have often
been seen stealing fish from other birds such as osprey. When fish
are not available, such as in winter, eagles will also feed on
waterfowl, small mammals (up to rabbit-size) and carrion (even
During Michigan winters, bald eagles are seen throughout the
state (almost all counties), while they nest mainly in the Upper
Peninsula (especially the western portion) and the northern
portion of the Lower Peninsula. These eagles don't really migrate,
they just move south enough to stay ahead of the ice and
congregate near open water. Immature birds may move further south.
When bald eagles reach maturity (at four to five years of age),
they select a mate, with whom they probably mate for life. In
captivity, they have been known to live to 50 years, but in the
wild, they probably don't reach much more than 20 years of age.
The beginning of the breeding season, from mid-February to
mid-March, consists of the establishment of a territory, nest
building and mating displays. The mating "cartwheel"
display begins high in the air with the two birds darting and
diving at each other, until they lock talons and drop in a
spinning free fall, until the last possible moment when they
separate. The nest is usually located in the tallest tree in the
area, often a white pine or dead snag. They are usually made of
sticks with a lining of grass and moss. Nests may be added to each
year until they reach enormous sizes, up to ten feet in depth and
20 feet across.
From late March to early April, one to four (average two) pure
white eggs, approximately twice the size of a chicken egg, are
laid. Both males and female bald eagles participate in the
incubation, and the feeding of the chicks that hatch around seven
weeks later. In about three months, by late summer, the fledglings
are ready for flight. When it is time to move for the winter, the
young birds are abandoned by their parents.
Before European settlement, bald eagles probably nested in all
regions of Michigan where food was available. In the early 1900s
they were described as being "generally distributed,"
but "nowhere abundant." A decline through the early and
mid-1900s was probably related to slow but consistent loss of
suitable habitat and available food, and predator control by
humans. These eagles are so disturbed by the presence of humans
near their nest that they may be induced to abandon the nest, or
even chicks that have already hatched. By 1959, the species was
considered, "largely restricted to the northern half of the
Through the 1950s, the slow decline accelerated dramatically,
until suddenly, bald eagles were on the brink of extinction in the
lower 48 states. The population crash was due to several factors
that had reduced reproductive success of nesting pairs, but was
mostly the result of increased use of pesticides with chemicals
such as PCB and DDT. These chemicals affected the eagles in many
ways, including causing them to delay their breeding until it was
too late in the season, or even to not breed at all. Eggs that
were laid often had thin shells, causing them to break in the
nest. At its worst in 1967, only 38 percent of the Michigan
population of bald eagles were able to raise at least a single
chick. Productivity must be at least 70 percent for a bald eagle
population to remain stable.
Recognition of the plight of bald eagles in the US and its
cause finally occurred in the 1960s. By the 1970s DDT had been
banned in the US. Intensive monitoring of eagles in Michigan began
in 1961. Although bald eagles had been protected at federal and
state levels since 1940 and 1954, respectively, they received much
greater protection after the ratification of the Endangered
Species Act in 1973, and the Michigan endangered species act in
Reproductive success began to improve and in 1975, the 70
percent productivity mark was reached, although it dropped off
again soon after. The population remained at around 86 nesting
pairs through the 1970s. In 1981, the population at last began to
increase. The 1999 survey found 343 nests that produced 321 young.
The productivity was calculated as 96% (young per nests with known
outcomes). But some problems still exist. Eagles nesting along the
Great Lakes coasts have higher contaminant levels in their blood
than inland nesting pairs.
The image of the bald eagle has had great significance in the
formation of our country and it finally looks as though it will
remain a part of the living history of the United States of
America, thanks to the stewardship of many concerned individuals
who continue to advocate for this species' survival.