Frozen
Dinner
The Challenge of Finding Food in Winter
by Laura Erickson
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Bald
eagle on perch alert to any potential food below .
Credit Laura Erickson
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Bringing home duck while mate watches from above
Credit Ray Foster |
Imagine
eating frozen meat without using your teeth. That’s something
Bald Eagles do often in the winter.
When
water is open in a good fishing river, of course, eagles don't have
to worry about crunching through ice, either on the water’s surface
or in their food. Even when the air temperature is 20 below zero, open
water cannot be colder than 32 degrees Fahrenheit, so fish may be cold,
but they’re not frozen.
But eagles
don't live on fish alone, especially in the winter. In northern areas,
eagles are often seen eating road-killed carcasses. During a cold spell,
how can they possibly eat rock-hard, frozen meat?
"Help" From
Other Animals
We
humans are lucky. Like other mammals, we have teeth. Birds don't. Eagle
beaks are designed to rip open fish and other kinds of meat, and their
mouths and throats are designed to swallow big chunks, but “ripping” is
hard when meat is frozen solid. So during winter, eagles often rely on
other scavengers to hack into the carcass before the eagles can pick
up and swallow loose chips of meat.
Ravens and
wolves are usually the first to dine on a carcass. Ravens use their
massive but straight, pointed beaks to hack away. Some carcasses are
small enough to hack just anywhere, but some are just too thick. A
sturdy deer hide is hard to break through even when the deer isn't
frozen. So ravens usually eat a deer from the inside out, pulling out
the guts from the opening under the tail. Once ravens start pecking
at the carcass with their beak, nearby eagles can pick up and swallow
flying chips of meat. And on sunny days, even when it's very cold,
the inside of the deer will be warmer than the air, and is often not
solid, so eagles can rip off chunks of the guts when the ravens pull
them out.
Wolves gnaw
their meat, and sometimes “play tug-of-war” while fighting
over larger pieces, which helps to break them down into more chewable
sizes. Again, Bald Eagles can take advantage of chunks they find.
Other
Strategies
Eagles also eat chunks of fish (sometimes frozen ones) they find near dams.
Swallowing a frozen fish chunk is like swallowing a piece of ice--it makes
an eagle’s tummy cold! Fortunately, eagles have thick feathers to keep
them well insulated, and they shiver. Shivering makes their muscles work hard,
which produces extra body heat to keep them warm.
Eagles have
other ways of finding food in winter. For instance, I’ve seen
them hunting for mice in a field. And sometimes eagles find their food
thanks to humans. When people are ice fishing, they often leave the
fish sitting out on the ice to keep them fresh rather than bringing
them inside their warm fishing huts. Sometimes eagles notice this and
fly in to steal the fish the moment the anglers are back inside their
huts! Some eagles come down to bait pots and take out minnows.
The oddest
winter eagle feeding strategy I’ve ever heard of was from a man
in Port Wing, Wisconsin. He attracted a Bald Eagle to his bird feeder!
Every morning the man set out a couple of hard-boiled eggs, and the
eagle flew down, ate the eggs, and flew off again.
Journaling
Questions
- How
many different food items can you name that eagles eat? What do all
of the foods have in common?
- Other
than hunting for fish, how many different hunting methods were described?
- How do
eagles do other animals in eagle habitats unintentionally help them
get the foods they need?
- What
other animals can you think of that have special strategies (behavioral
adaptations) for finding food in challenging conditions? Describe
the strategies.
Try
This! Scavenger Hunt for Eagle Food
Write a list of eagle winter food items for a “scavenger hunt” game.
Which of the items on your list can you find in one day? An eagle eats 5-10%
of its body weight each day. Do you think you could find that much food on
your hunt? (First, find out what an average eagle weighs.) How much food would
you need in a day if you were to eat the same percent of your weight as an
eagle eats?
National
Science Education Standards
- Organisms
have basic needs. They can survive only in environments in which
their needs can be met.
- Each
plant or animal has different structures that serve different functions
in growth, survival, reproduction.
- All organisms
must be able to obtain and use resources, grow, reproduce, and maintain
stable internal conditions in a constantly changing external environment.
- An organism's
behavior patterns are related to the nature of that organism's environment,
including the kinds and number of other organisms present, the availability
of food and resources, and the physical characteristics of the environment.
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