How do birds reproduce? We know that chickens lay eggs. But how do they do that?
It all starts with behavior aimed at attracting a mate. In birds, this will involve a type of display, usually performed by the male. Some displays are very elaborate and may include dancing, aerial flights, or wing or tail drumming. Most male birds also sing a type of song to attract females. If they are successful at attracting a female, it will lead to breeding.
Birds reproduce by internal fertilization, during which the egg is fertilized inside the female. Like reptiles, birds have cloaca, or a single exit and entrance for sperm, eggs, and waste. The male brings his sperm to the female cloaca. The sperm fertilizes the egg. Then the hard-shelled egg develops within the female. The hard-shelled eggs have a fluid-filled amnion, a thin membrane forming a closed sac around the embryo. Eggs are usually laid in a nest.
Why do you think eggs come in so many different colors? Birds that make nests in the open have camouflaged eggs (Figure below). This gives the eggs protection against predation. Some species, like ground-nesting nightjars, have pale eggs, but the birds camouflage the eggs with their feathers.
To protect their young, different species of birds make different nests. Birds of all types, from hummingbirds to ostriches, make nests. Many can be elaborate, shaped like cups, domes, plates, mounds, or burrows. However, some birds, like the common guillemot, do not use nests. Instead, they lay their eggs on bare cliffs. Emperor penguins do not have a nest at all; they sit on eggs to keep them warm before they hatch, a process called incubation.
How else might a bird help protect its young from predators? Most species locate their nests in areas that are hidden, in order to avoid predators. Large birds, or those that nest in groups, may build nests in the open, since they are more capable of defending their young.