Eagles,
Fish, and the Food Chain
Largemouth
Bass
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Eagles eat
fish — A LOT of fish. They are also are "opportunistic" in
their feeding habits. Their diet varies with the season and with what is
available, but fish is their number one food choice. Other foods include
certain birds (waterfowl) and an occasional turtle. Some reports tell of
bald eagles feeding on deer, whales, or other large animals, but in those
cases the eagles found the dead animals and did not kill them.
An eagle's
average daily food consumption is from 250-550 grams per day, or between
5-10% of an eagle's body weight.
Sunlight Fuels the Food Chain
Bald Eagles, like other animals, get all their energy from the sun. Of course,
they could sit out in the sunshine their whole lives and die of starvation!
So, how can the sun be the source of their energy?
Let's start
at the beginning. Sunlight is the source of energy for plants. Using
the sun's energy, green plants produce food through photosynthesis.
Tiny plants called algae grow in lakes. Without the algae, there would
be no food for any of the animals, and without the sun, there'd be
no algae. Read on to see how the chain unfolds.
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Green
Algae |
Water
Fleas |
Nymph |
Algae
are the main source of food for little animals called daphnia or
water fleas.
- It takes
about ten grams of algae to grow about one gram of tiny water fleas.
Some aquatic
insects eat these tiny water fleas. An example is the dragonfly nymph.
Dragonfly eggs hatch into nymphs that live in the water for months
or even years. When they leave the water they shed their final nymph
skin, and open up their wings to become adults. When these adults breed,
they will lay their eggs in the water to start a whole new cycle.
Dragonfly
nymphs eat many little creatures in the water, including water fleas:
- It takes
about 10 grams of water fleas to produce about one gram of insect.
Small
fish eat many aquatic insects, including dragonfly nymphs:
- It takes
about 10 grams of insects to produce one gram of small fish.
Some
medium-sized fish eat smaller fish. An example is the largemouth
bass:
- It takes
about 10 grams of smaller fish to produce one gram of these medium-sized
fish.
In
turn, the medium-sized fish are food for large fish:
- It takes
about 10 grams of medium-sized to produce one gram of these large
fish.
Finally,
the large fish are food for other living things — like
eagles!
- It takes
about 100 grams of large fish to produce one gram of eagle.
Why does
the eagle need so much more food for its weight than fish, insects,
or water fleas need? (Hint: Consider whether a species is warm-blooded
or cold-blooded, and what this would mean for food requirements.)
Try This!
- A food
chain is a simple drawing that illustrates how each animal eats some
things and is eaten by others. Have individuals or small groups of
students ilustrate the eagle's food chain starting with the sun and
going all the way up to the eagle. Include labels for each "trophic" (food)
level and a title for the completed page.
- Students
can create illustrations for each part of the eagle's food chain,
or print
the illustrations from this page.
- Students
may want to add facts or math questions to their food chains to challenge
other students.
- Food
chains are one way of showing the food levels. Another way is a food
pyramid. For example, a food pyramid for eagles would have a large
base: the algae. Ten thousand pounds of algae would produce a thousand
pounds of daphnia, so this level of the pyramid would be smaller.
A thousand pounds of water fleas would produce a hundred pounds of
tiny fish. Use this information to draw an eagle's food pyramid.
National
Science Education Standards
- All animals
depend on plants. Some animals eat plants for food. Others eat animals
that eat plants.
- For ecosystems,
the major source of energy is sunlight. Energy entering ecosystems
as sunlight is transferred by producers into chemical energy through
photosynthesis. That energy then passes from organism to organism
in food webs.
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