The nesting method used by birds depends upon their size, location and diet. It also depends on the available nesting materials and the reproductive habits of the given bird species. Some do not build nests at all, but take advantage of existing structures for shelter and egg protection.
The most basic approach to nest construction is scraping. Scrape nests are used by ducks, many shorebirds, quail, pheasants, ostriches and several other species. These nests are shallow depressions dug into sand or soft soil and used to keep eggs in a single, safe place. Scrape nests are particularly useful in Arctic climates because they protect the eggs from freezing winds.
Cavity nests are another common type. Birds that build these nests use their bills to hollow out portions of trees, cacti, adobe structures and other pliable objects. Cavity nests protect eggs from severe weather conditions and from most predators. Species that build cavity nests include woodpeckers, tits, bluebirds, hornbills, some parrots and selected duck species.
Birds that build cup nests use a mixture of organic debris and saliva or mud to build bowl-shaped structures in trees, shrubs and beneath rocky outcroppings. According to the Cornell University Laboratory of Ornithology, cup nests are the preferred nest type for hummingbirds, swifts, flycatchers, blackbirds and other small birds.