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The Bald Eagle
by Janice G
Class 703- Dolphin Senior Public School
Mississauga, Ontario
Introduction
Even though the Bald Eagle is one of the most recognized birds, only a
few people have seen it. The reason for this is the death rate of eagles
that occurred in the 1950's. Thanks to Canadian Charles Broley and scientist
Rachel Carson in 1973, an Endangered Species Act granted the Bald Eagle
full protection. The eagle population is now slowly rising. Just recently,
the Bald Eagle was removed from the endangered species list in the United
States. The North American Bald Eagle is the symbol for the United States.
It decorates many American belongings such as government buildings, quarters
and silver dollars. Its scientific name is Haliaeetus Leucocephalus (meaning
white-headed eagle). On average, male Bald Eagles measure 90.5 cm from
head to toe. They have a wingspan of approximately 200 cm. and weigh about
3 to 4.5 kg. Females are larger than this. They weigh about 6 kg. and
have a wingspan of 98.5 cm. The eagles' head and tail are white, and its
body is dark brown. Long ago, bald headed meant white headed. That is
how the eagle got it's name.
Features
Classification
The Bald Eagle is part of the sea and fish eagle group, one of four groups
that eagles are divided into. Sea and fish eagles mostly feast on water
animals. Eagles are also called raptors, birds of prey. This means that
they eat other animals. The Bald Eagle is a Falconiformes raptor, raptors
that hunt mostly during the day.
Size
The size of Bald Eagles can be different, depending on its age and gender.
Young eagles are often larger than adults. This is because a young eagle's
tail and wing feathers are longer than an adult's feathers. Even though
this may be, young eagles still weigh less than adults. Like most birds
of prey, the females are larger than the males. This helps females defend
their nests, eggs and young. The males, being smaller, can manoeuvre more
easily.
Eyes
and Vision
The eagles eyes are probably the most sharpest eyes in the world. It can
see 4 to 8 times better than human eyes. Eagles have 2 focusing depressions(foveae)
in the retina of each eye. This can allow the eagle to look forward and
sideways, at the same time. They also have a much greater resolving power
than human eyes. Eagles have 2 eyelids. The inner one moves from front
to back every 3 to 4 seconds. It wipes dirt and dust from the eye.
Feet,
Talons and Beak
Bald Eagles have very strong feet. The undersides of their feet are very
rough and bumpy. The eagles have 4 toes, 3 in the front and 1 in the back.
On the tips of their toes are long, curved talons which they use as weapons(when
needed). Bald Eagles have no teeth. They swallow their food in pieces.
They use their beaks to tear their prey in pieces. Sometimes, to finish
the life of its prey, the Bald Eagle uses its hooked like beak and jabs
its prey. Skeleton The Bald Eagles is skeleton is thin, hallow and filled
with air spaces. Many of the bones are joined, which makes the eagle strong.
This kind of skeleton helps raptors to fly. An eagle's skeleton weighs
less than half the feather's weight.
Distribution
and Range
Most
eagles migrate regularly from a summer range to a winter range, and back.
The Bald Eagle migrates southward, mainly during October and November,
to its wintering grounds. The majority of them winter in southern United
States and Baja California. In late winter and early spring the Bald Eagle
migrates back to Alaska and Northern Canada. It travels in the afternoon
unlike in the fall migration. This is because in spring, the availability
of thermals (columns, or currents, of warm air that rise up in the sky)
are only at its best in the late afternoon, due to the bad weather. The
Bald Eagles' habitat consists of tall trees, large bodies of water, rocks,
cliffs and open spaces such as beaches and sandbars. This allows it to
roost, perch or catch and kill prey. In the cold months, which the Bald
Eagle can survive, the water usually freezes over. So when the eagle winters,
it will most likely hunt or find prey on land instead of in the water.
Or, it moves to southern areas of open water. There are Conservation Groups
and Rehabilitation Centres across North America. They are helping to protect
the areas where eagles live, and to pass laws to control pollution.
Food
Bald
Eagles are scavengers and hunters. They eat a variety of foods. Its diet
mainly contains fish, birds and mammals. They prefer to eat fish, and
waterfowl the most. The fish that they eat are often poisoned. This is
how:
PREDATOR PREY
- Bald Eagle eats Fish
- Fish eats Smaller Fish
- Smaller fish eats Plankton
- Plankton absorbs Pollution
Even though healthy Bald Eagles are able to go a week without food, they eat 6 to 11 percent of their body weight everyday. Bald Eagles need this in the winter because they use more energy to keep warm. Photoperiod plays a major role on the eagles' diet. It allows the ice to melt so eagles can catch fish. Also, it lets plants and insects grow or live. Animals that eat plants and insects have food. These animals are food for other animals, like Bald Eagles. In the winter, it does the opposite. Photoperiod also tells eagles when to migrate, breed, and when to molt their feathers. When the water turns into ice, eagles can no longer eat fish. This is when they steal and scavenge carrion. Eagles only hunt for small animals when they cannot find or steal prey. Some birds try to fight for their food. They almost always shamefully lose to the Bald Eagles sharp talons and pointy beak.
Physiology
The
temperature and weather affects the way a Bald Eagle would go about its
daily routines. If on its summering grounds the temperature gets to hot,
a Bald Eagle would fly south to a warmer spot. If it is freezing, a Bald
Eagle may not find food, and die of starvation. Usually, in cold temperatures,
Bald Eagles eat more to get energy and stay warm. A drought affects virtually
the whole food chain. Plants would have no water and die. Insects would
die because there are no plants, and so would deer, geese, ducks and rodents.
The population of animals that feed on insects and these animals start
to decrease. That leaves less food for the Bald Eagle.
Reproduction
The
mating season of the Bald Eagle usually occurs during mid-May, after the
coldest weather has passed. If eggs are laid too early, the embryos may
freeze. Once Bald Eagles have found a partner, they mate for life. If
one of them were to die, the other one would find another partner. Couples
mate by doing a Sky Dance. (refer to the next page for a diagram of the
Sky Dance)
If a couples' eyries (currently used and back- up nests) were destroyed, the two birds would not mate. Instead they would start building other eyries. Female eagles lay between 1 and 4 eggs. Most often 2. The eggs are laid 2 to 4 days apart. The first egg is usually largest and heaviest. After incubating in an eyrie for about a month, the first egg hatches, the others in the following days. The next few weeks are very busy for the parents. When the eaglets squeal in a food begging call, the parents quickly bring food to the nest. Parents have to rip the prey into small pieces for the young to eat. Feeding takes place every 3 to 4 hours. After 6 to 7 weeks, the eaglets are able to rip the prey by themselves, leaving the parents easier jobs. By the migrating time, the eaglets have learned to do a lot without the help of their parents. They start to migrate earlier than the adults, and arrive latest at their wintering grounds. Some may die of starvation if they are lost and unable to find a good wintering spot. On average, a Bald Eagle lives 30-40 years.
Conclusion
Eagles
have a troubled time looking for food when lakes and rivers are frozen,
and a thick layer of snow covers the ground. So in the fall, when the
days get shorter, Bald Eagles get an urge to migrate, due to the cold
weather. That is why they travel south to a warmer climate.
In the spring, eagles fly north for many reasons. Some of the best advantages
of migrating north are to do with the available territory, weather and
availability of thermals in the spring. Up north, in Alaska and Northern
Canada, there is much room for eagles to build eyries, start a family,
and to roam through the sky. The weather is neither hot or cold. During
the spring, the temperature usually ranges from cool to warm. The weather
is not too harsh either. These temperatures are most favourable to eagles.
Thermals are most available during the migration time in the spring. This
makes it easier for Bald Eagles to migrate north. According to the Journey
North Migration Map, most Bald Eagles have already made it to British
Columbia, Canada. It is predicted that, between April 11th, and April
18th, the majority of Bald Eagles will have reached their destinations,
some quicker than others, depending on how far their destination may be.
Bibliography
Books
- Dudley, Karen. Bald Eagles, Weigl Educational Publishers, 1998
- Gray, Ian. Birds of Prey, Wayland Publications, 1990
- K.Peck, George. Hawks and Eagles, Smart Apple Media,1998
- Lang, Aubrey. Eagles, Key Porter Books, 1990
- Lee, Sandra. Bald Eagles, The Child's World Inc., 1991
- Penny, Malcolm. The Eagle, Boxtree Limited, 1990
- Ryden, Hope. America's Bald Eagles, P. Putman's Sons, 1985
- Stalmaster, Mark. The Bald Eagle, Universe Books, 1987
CD-ROM
- Encarta 97. Eagles, Microsoft, 1997
Internet
- Dogpile: www.dogpile.com
- Journey North: www.learner.org/jnorth
- More About Eagles: www.eagles.org/moreabout.html
- U.S Climate: www.cdc.noaa.gov/usclimate/states.fast.html
- Yahooligans: www.yahooligans.com
Video
- Nova. Mystery of Animal Pathfinders
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