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What kinds of animals lay eggs?
All birds, turtles, lizards, fish, reptiles, dinosaurs, most insects, worms,
arachnids, amphibians, but very few mammals, lay eggs. Many animals lay
eggs in water, on leaves, or in nests. These eggs have a covering that protects
the developing creature.
What is an egg tooth?
Some embryos have a temporary egg tooth with which to crack or pip the
eggshell or covering.
(a) Find out how chicks break out of the egg.
(b) Draw pictures to show the hen's egg tooth.
Oology is the study of eggs.
Some snakes specialize in eating eggs.
raccoon skunk mink river and sea otters
gull crow fox stoat
Eggs come in many different colours and shapes.
Can you guess why this might be useful?
Some eggs have markings and colours that make them look like their
surroundings - this way predators have a harder time finding them.
Eggs are not all the same shape as the chicken eggs that we eat. Egg shape is
determined by the internal structure of the hen. Egg shapes, over time, are
often closely matched to their nest environment.
• Some eggs are very pointy at one end (conical). These eggs are laid by birds who
make their nests on cliffs and ledges. The pointy eggs roll in very tight circles so they
don't fall off .
• Shorebirds normally lay four pointed eggs. In the nest, the eggs are oriented with their
pointed ends towards the centre. This minimizes the amount of space needed to form
the nest and increases the efficiency of the heat transfer from parent to egg during
•In contrast, many hole-nesting birds have nearly spherical eggs.
It takes 60 ostrich eggs to equal the weight of one ostrich,
but only nine hummingbird eggs to equal the weight of the hummingbird.
It takes only four kiwi eggs to equal the weight of a kiwi.
Fortunately, female kiwis lay only one and occasionally two eggs per year.
hen and kiwi bird eggs
hen kiwi bird
List animals in descending order according to what the students think the egg
size is. Students can later measure actual eggs of various sizes and record on
Eggs play an important role in the life cycle of many creatures such as butterflies,
birds, bees, frogs, and dinosaurs.
Use pictures to compare and contrast eggs from a variety of different
birds and animals according to size and colour.
Discuss who laid them. Describe the colour, size, and shape of the egg
including turtles, chickens and dinosaurs. Try to explain why they look the
way they do.
What is in an egg?
Break a raw egg onto a saucer or into a bowl.
Look at it carefully.
Eggs are a good source of protein in our diet. The nourishment that eggs provide
for us would otherwise have provided the embryo with sustenance.
Inside an egg shell is a yolk, embryo, albumen (white), and membranes. The
contents of the egg are used as food for the developing embryo.
Eggs - can be soft-shelled or hard-shelled. They have everything inside needed
to produce a baby bird.
Note: Hens must mate with a cockerel to make a chick. The eggs we eat are not
fertilized, so they would not develop into baby chicks.
Touch the yolk and the layers of white with your finger and think about how
it feels and smells. Touch the thin, papery, white skin that is stuck to the
shell and peel some off. How does it feel? If you let it dry, will the texture
change? Test it out.
Remember to wash your hands after this experiment.
The egg contains nutrients e.g. proteins, carbohydrates, fats, vitamins, & minerals.
People have collected and eaten eggs for thousands of years.
If an egg is fertilized, it develops into an embryo which grows into a baby
animal like the parents. The egg must provide all of the things a growing
warmth, protection, and food – it's an amazing package containing an
embryo and all the food it needs to grow. It has a protective covering (the
shell) that keeps it from drying out too fast and helps to keep the dirt out.
Draw, colour and label the parts of the egg:
shell, yolk, albumen, embryo.
How does an egg grow into a baby?
The process is called incubation.
What is required for incubation to be successful?
- The egg needs to be fertilized
- The egg needs to have been laid with sufficient nutrients to let the baby grow
and thrive until it hatches
- The egg needs oxygen
- The egg needs sufficient heat & moisture
- Some eggs need motion (to be moved or turned)
- How are these things provided during incubation? –
- The nutrients are all there when laid
- Fertilization is usually there when laid (most fish & amphibians and some
insects do this after the eggs are laid)
- Oxygen passes through the pores in the shell
- Heat & moisture are there as eggs are laid in a moist, warm place or provided
by the mother when she sits on them.
Birds’ eggs may be either chicken eggs (real) or speckled candy eggs
(model) that have a hard shell.
Model reptile eggs may be made by hard boiling chicken eggs, then
soaking them overnight in vinegar which makes the outer shell soft.
Finally stain them brown by soaking them in cold coffee for an hour. Let
the eggs dry, which will make them slightly wrinkled.
Model amphibian eggs can be made by soaking large pearl tapioca in
water for a few hours.
Fish eggs can be made by soaking small pearl tapioca in water (model) or
you can buy a jar of inexpensive caviar for the real thing.
Prepare model eggs for discussion, to describe, draw and display:
(birds, reptiles, amphibians, fish). Design them to represent real-life models:
When you distribute eggs, try to keep close to the numbers in nature; only pass out
3-5 bird eggs per group, but make sure the fish egg container has hundreds.
Remember: While birds and reptiles are often able to build nests to camouflage and
protect their eggs from predators, fish and amphibians' eggs are usually exposed to
predators. For this reason, sometimes few eggs survive.
Why are some eggs soft and some hard?
Where are they laid?
Why does the hen sit on the egg?
Predict how many of the eggs they see in the samples might survive to develop
to maturity. Do you think all of them would? If all of the eggs you see hatched,
how many birds would there be? How many fish?
(Note: If an animal lays large numbers of eggs, it is likely that many of them are eaten
by carnivores. The animals that experience these high mortality rates lay lots of eggs
to avoid extinction.)
Now try these:
• Make a list of animals that lay eggs and discuss out how the baby animal inside
gets the protection and air that it needs to survive.
• Make a chart showing animals that hatch from eggs.
• Create a game matching the eggs, babies, and animals.
• A clutch is the total number of eggs laid by one bird during one nesting.
• The average clutch sizes range from one (as in condors) to about 17
• Female kiwis lay only one and occasionally two eggs per year.
•The toucan nests in tree holes laying 2–4 white eggs.
• An adult female cod can produce 4–6 million eggs in one spawning.