Building a home
Unlike most reptiles and mammals, many birds build their own homes - their nests. Each species nests in a different way, according to where it lives.
How to build a nest
Most choose a place that is hard for predators to spot or reach. Some, such as dunnocks, nest deep in a thorny bush. Others, such as guillemots, nest high on a cliff. Many, including owls, blue tits and woodpeckers, choose a hole in a tree.
Keeping it simple
A nest can be very simple. Ringed plovers just make a shallow scrape in the beach and lay their eggs directly onto the ground. Their eggs and chicks are camouflaged to look just like shingle. Some birds don’t even make their own nests. Buzzards often take over disused crows’ nests, and house sparrows sometimes use the old nests of house martins.
Materials and designs
The size and shape of nests varies from one bird to another, and partly depends on what building materials are around. Long-tailed tits line their nest of twigs with feathers, and cover it with moss and lichen. Swallows use soft mud to glue their straw nest together. African sociable weavers build a huge grass construction with many entrances. It can house over 300 birds and last for a hundred years.
Cuckoos never build a nest; instead they lay their eggs in another bird’s nest, such as a dunnock’s. As soon as the baby cuckoo hatches, it pushes out the dunnock’s own eggs. The adult dunnocks feed the imposter until it fledges – though it soon grows much bigger than they are.
Warming the eggs
Eggs need to be kept warm until they hatch; this is called incubation. A bare patch of skin on an adult bird's belly, called the brood patch, transmits its body heat to the eggs as it sits on them. With many birds, males and females take turns but each species has its own arrangement.
Male emperor penguins incubate a single egg on their warm feet, while the female is away feeding. They do this for 60 days, never eating and not once letting the egg touch the freezing ground.