Some birds hunt other animals to get their food, while some have to be
on guard against animals that want to hunt them. Can you tell the difference
between a hunter and a hunted bird?
Who eats what? In this experiment you put out a variety of foods,
and figure out which birds come to each kind.
Some good food can be hard to get at. Birds have evolved beaks that are
very good at gathering their special food. Can you figure out what a bird
eats by looking at it's beak? It's easier if you compare the beak to tools
you already know.
Attract certain kinds of birds by putting out specific foods. We show
DDT is a chemical that used to be sprayed on crops to kill insects.
It's illegal in the US now. This picture shows how DDT harmed the
Ospreys. Click on any of the five steps for details.
Demonstrate the surprising strength of eggs.
2 dozen eggs of equal size
4 egg cartons
hardback books of equal size and weight, at least a 2-foot stack
Ask the students if they know how strong is an eggshell. Write down
the answers on the board.
Explain that you are going to squeeze an egg on either end and it will
Students will estimate how many books can be stacked on top of four
Place four eggs of the same size in the second and fifth rows of an
open egg carton, pointed ends down.
Carefully place one book, (one with a surface that you can wipe clean)
directly on top of the eggs, and continue adding books, one at a time,
balancing the pile as you go.
See how tall a tower you can make.
Discuss your results.
An egg's dome shape makes it resistant to compression. That's why
a mother bird can sit on her eggs without breaking them. On the other
hand, eggs and other dome shapes are weak in tension, a force outward,
so that a baby bird can easily peck its way out when hatching.
Demonstrate and explain how chemicals can effect an eggshell.
cup or jar to hold eggs
First complete the egg strength experiment.
Ask: How has DDT affected Bald Eagle and Osprey eggs. Place an egg in
a jar or cup, and cover it with vinegar.
NOTICE bubbles forming on the surface of the egg. This is a chemical
reaction between the acid in the vinegar and the calcium carbonate in
Leave the eggshell in the vinegar overnight.
Next day, examine: the shell will have gradually dissolved, leaving
behind an egg inside a soft membrane.
Chemicals in an animal's food or water can cause strange things to
happen. You saw how DDT affected the osprey's eggs. Now you will do
your own study to see the effects of vinegar on eggshells.
Unsafe water can come from far away, and result
in surprising things. The Osprey is a fish-eating bird that nearly went
extinct because of farmers spraying their crops. How is that possible?