Newsgroups: rec.scouting
Subject: Egg Power
From: jim.speirs@canrem.com (Jim Speirs)
Date: Fri,  6 Jan 95 07:10:00 -0500

Article #R42.
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Egg Power
Ben Kruser
The Leader, April 1992.


Eggs are common household items that offer a wealth of
interesting natural history lessons and some fascinating program
activities.  The next time you are cracking eggs for a camp
breakfast, take a moment with the Cubs to explore the fascinating
world of the egg.

Natural History 

Eggs werek a major evolutionary development for birds.  They
greatly enhanced the probability of survival because the shell
could contain large food stores.  They also allowed birds to
penetrate into drier habitats.  Yolk fat, when broken down,
yields more metabolic water than the primarily protein food in
reptile eggs. Consequently, reptiie eggs still need some external
moisture for development, which probably is one reason reptiles
seek out damp earth in which to bury their eggs.

In evolving into flying animals, birds developed a means to
excrete waste that has positive benefits to eggs.  As a
weight-reducing adaptation, birds do not have bladders.  The
moisture in their food is absorbed by the body, and the resulting
waste is uric acid, which is insoluble in water.  This insoluble
substance is ideal in a closed egg, since it prevents the
developing embryo's waste from mixing with the yolk and poisoning
its producer.

Eggs come in an sorts of "egg shapes" and sizes.  If you
scrambled up a single Ostrich egg, you could feed 12 people.  At
the other end, the tiny Vervain hummingbird of Jamaica lays an
egg only 10 mm long.

The largest known bird egg is that of the extinct Elephant Bird
of Madagascar.  Fossil eggs measured 34 cm by 24 cm and held 4.5
L.  One Elephant Bird egg could hold 33,000 Vervain Hummingbird
eggs, for example, and the shell was heavy enough that Madagascar
natives could use it as a bowl.

Most birds lay eggs relatively the same shape and size as others
of their species.  The exception is the parasitic European Cuckoo
which lays its eggs in the nest of other birds.  It varies its
egg size to match those in the nest so that the parent bird
doesn't reject the Cuckoo egg and push it over the nest edge. The
Cuckoo can also lay eggs with coloration to match the host's eggs
-- another way to camouflage its work.

Shorebird eggs are more pointed at one end and rounder at the
other.  This causes the egg to roll in a right circle,
particularly advantageous for cliff-nesting shorebirds whose eggs
are at risk of rolling away and over the cliff edge.


Eggs come in a variety of colors ranging from browns and reds to
blues and greens.  They may have streaks, dots, or blotches. 
Cavity nesters and open nesters that cover their eggs with down
or vegetation when they leave the nest (some ducks, geese,
grebes) usually lay white eggs because there is little need to
hide them from sight.  White eggs in cavity nests may also help
the parents see the eggs in dim light.

Egg Activities

Why are eggs round and not square?  Dome shaped structures are
exceptionally strong because the weight is carried along the
curved walls to a wide base; no single point on the dome supports
the whole weight of an object on top of it.  That is why
architects use dome structures for big buildings that can't have
supporting pillars, such as concert halls or hockey arenas.  It
is also why eggs don't crack when the parent bird sits on them.

This weight-bearing property can lead to some interesting
activities with egg shells.  If you're using eggs at a camp, have
the Cubs try this experiment while the food is cooking.

Take four eggs and gently break open the small ends by tapping on
a hard surface.  Carefully peel away some shell and pour or scoop
out the insides.  Put some masking tape around the egg's middle
and carefully cut around the egg shell, through the masking tape,
so that you have four half shells with even bottoms.

Put the egg shells on a table or floor, open end down, and place
a book on top with an egg shell under each book corner.  Keep
adding weight until the eggs crack.  See which six can add the
most weight.  The Ontario Science Centre in Toronto has shown
that a single egg can support a person weighing 90 kg!

The next time you are overwhelmed by today's technology, reflect
for a moment on the simplicity and genius of design in the lowly
egg. 

Resources

Science Works: An Ontario Science Centre Book of Experiments,
Kids Can Press, Toronto, 1984

The Life of Birds, by Joel Carl Wetly; WB Saunders, Toronto, 1975

Program Links
Observer 2; World Conservation 1f