Original by Dr Margaret Rowe, 2002
Last revised by the Department of the Environment and Heritage, December 2004
ISBN 0 6425 4820 X
Reproduction and development
After mating, fertile eggs are produced. Egg production uses a lot of energy and females must be well fed if they are to produce eggs. There some types of bird, like domestic chickens, that can lay an egg nearly every day. Most birds only lay a few eggs per year, during the breeding season. Shorebirds lay a clutch of no more than four eggs once a year.The eggs contain all the food and water needed for the tiny chick to grow.
Eggs vary in shape from almost round to oval "pointed" shapes. Many shorebirds, gulls and terns lay their eggs in very shallow, saucer-like depressions in the dry sand. Their pointed eggs do not roll away easily. The deeper nests made by other birds hold eggs safely, and their eggs are more oval or round in shape.
In some birds it is important that the eggs are well camouflaged. This is true for many shorebirds and terns that cannot guard their eggs all the time. The splashes of colour on the shells blend with the surroundings, making it unlikely that predators will see the eggs.
Use plasticine, clay or playdough to make eggs of the two different shapes illustrated here. Try rolling them.
Chicks hatch by using the special "egg tooth" on their bill to chip a big hole in the shell of their egg. The movements of their body then usually shatter the egg.
The chicks of some types of bird are naked and helpless when they hatch. They have a huge appetite and depend on their parents to bring food, and provide a clean, warm nest.
Shorebirds hatch with a thick coat of down and can run about. In most species, chicks can feed themselves shortly after hatching. They are camouflaged well and their parents keep an eye on them, protecting them from predators. In the species that do rely on their parents for food, it is often the male that cares for the chicks.
The newly hatched chicks of gulls and terns also have a thick covering of down, but they take a little longer to become mobile.Their parents bring fish for them until they are old enough to fly and hunt for fish themselves. Their parents protect them from predators.
Small species of birds can live up to about 5 years. Larger species can live to the age of 20 to 40 years or more. Most individual birds die before they reach these ages. Small shorebirds can live for nearly 20 years and larger ones probably live longer than this.
Figure 11 Eggs of shorebirds and terns are more pointed than the typical bird's egg