All birds lay eggs; of the 9,000 species of birds, none of them give live birth. Instead, birds form and lay eggs that are incubated outside the body. Eggs range in size depending on the bird and can be as small as 0.2 grams or as big as 9 kilograms.
Birds lay and hatch eggs in places that are inconspicuous and away from predators. This is accomplished in a variety of ways, depending on the species of bird. For example, the African palm swift uses its saliva to glue the nest underneath a palm frond, while the swiftlet builds its nest on the ceiling of a cave.