Click to play Read by Matthew
Reproduction - How many?
Birds laying eggs is another good trick of nature. Birds are creatures that fly, so it would be very difficult for them to fly with their babies inside them because of the weight. Think about how "fat" mammals get when they are pregnant, or how wide frogs can get carrying all those eggs inside. So laying eggs makes sense for birds.
Normally, the shorter a birds life the more eggs it will lay. This is because the eggs, and chicks, are new lives of that species. So birds like Blue Tits lay many more eggs than a Barn Owl family. A Blue Tit's life expectancy is 2 years, whereas a Barn Owl will live 4 years in the wild.
What about sea birds?
Seabirds can live for many years so they usually only lay one egg. The Guillemot, Razorbill, Kittiwake and Fulmar are all sea birds - they get their food from the sea. These birds make their nests on cliffs - sometimes in very small spaces! But luckily their eggs are more of a cone shape so that if they do get knocked they roll around in a circle, rather than fall of the edge.
Laying and hatching
Different birds do different things!
The Mallard duck will lay an egg each day in its nest. The female Mallard might lay up to 14 eggs. So it will take 14 days for all the eggs to be laid into the nest. The eggs must be safe so they are covered with nest material to hide them. The female Mallard will then incubate the eggs. In other words, once all the eggs are laid she will keep the eggs cosy and warm helping the chicks inside the eggs to grow and develop. The eggs will then all hatch on the same day! The ducklings will stay in the nest for about 12 hours with their mother keeping them warm. As soon as it is safe to leave the mother Mallard will lead her ducklings to a pond. The ducklings will take their first swim on the first day outside of the egg. If the weather is too wet or cold the mother duck might keep her family huddled up for longer.
The Blue Tit's egg laying pattern is very similar. The female lays an egg each day, into the nice cosy nest. When all her eggs have been laid (sometimes an amazing 16 eggs!) the female will incubate the eggs. The female has a special patch on her tummy called the brood patch. She will pull out the feathers so that her warm skin is close to her eggs. The eggs will hatch at about the same time and the chicks will grow up together. When they are strong enough they will leave the nest.
Barn Owls have a different plan. The female lays the egg, about 2 days apart. The eggs are kept warm straight away. The eggs will then hatch on different days. This means that the first chick to hatch will be the biggest chick and the last chick to hatch will be the smallest. So if food is difficult to find, the bigger chicks get fed first and the smaller chick may not live. This is very sad. It does mean that when there is plenty of food around the Barn Owl will have 3 or 4 chicks that grow big enough to leave the nest in about July.
Top right: Barn Owl
Top left: Blue Tit with eggs
Bottom left: Female Mallard duck Bottom right: Brooding Patch