Birds seem to construct their nests instinctively, with each individual bird species building a nest in the same manner and out of the same materials that the other birds of that species do. A variety of materials, from twigs to the down from feathers, are used to create these nests.
The nests of birds are used to keep the eggs laid in them and the young birds hatched in them safe from such dangers as bad weather and potential predators.
One of the simplest kinds of nest is known as a scrape nest, which is, in essence, a depressed area made by the bird in the ground, with species such as penguins, gulls and vultures employing this method.
Cup-shaped nests can be made by a bird on the ground, placed on and supported by branches in a tree, built in such a way that the sides of the branch hold up the nest, or they can be "glued" perpendicular to a surface using substances like saliva or mud.
Birds that reside by rivers and streams like kingfishers will burrow into the dirt on the banks and make a nest; birds like owls and woodpeckers will make a nest in an existing hole in a tree.
Birds like the house wren will actually use spider egg sacs as one of the materials in their nest; the spiders that hatch from these will eat the parasitic mites that infect the nest area.