Female birds lay eggs in which their offspring develop until they are ready to hatch. Other animals like turtles and crocodiles also do this.
Even mammals, the group to which humans belong – include egg layers (the echidna and platypus).
There is a good reason why all bird species lay eggs, and it relates to their flying way of life. It would be difficult or impossible for a bird to fly or take off if it was carrying a large baby inside its body (as most mammals do) because of its weight, so birds offload their eggs as soon as they can. But this presents a problem: how do they keep them safe from the many animals that like eating eggs?
The answer, of course, is nests.
Most songbird nests are cup-shaped and are constructed with sticks, twigs, grass, vines or mud, or a combination of these materials.
However, many Australian songbirds build almost circular domed nests with a side-entrance. Some species are skilled at weaving grass to make nests, and others actually stitch leaves together by making holes with their bills and pulling grass through them.
Australasian Figbird by Greg Nye. CC BY-NC-SA 4.0 International
Willy Wagtail by Neil Humphris. CC BY-NC-SA 4.0 International
Many birds, such as parrots and owls, nest in holes in trees, while others, such as seabirds and bee-eaters, dig a tunnel in the earth, and make a platform of grass or woodchips at the end of it.
And finally many shorebirds, such as the Plovers, do not make a nest at all, preferring to lay their eggs on the ground where they seem quite vulnerable. But such birds will physically attack potential nest robbers when they approach, or use distraction displays to lure them away
Parent birds must sit on the eggs (called “incubating”) to keep them from getting cold, and this usually takes around two weeks for songbirds, but up to two months for bigger birds.
When chicken or plover eggs hatch, the chicks emerge covered in down, and are ready to run away and feed for themselves. However most songbird chicks are naked and blind – like human babies – when they hatch, so their parents must sit on them (called “brooding”) to keep them warm for 2 weeks or more.
Text © Richard Noske 2019 CC BY-NC-SA