Birds as small as hummingbirds and as large as herons nest on tree branches; so do hawks, owls, and crows. The nests may be found at every level of the tree, from the crown to the under-story. They may be near the crotch, between branch and trunk, or out toward the end of a branch. Birds may use maples, pines, junipers, oaks, sycamore, and palm trees for nesting.
Some birds such as certain sparrow species use grassland and brushy areas, making the nest on the ground.
Species such as wrens, juncos, and finches may build their nests in bushes and shrubs with dense, compact foliage, or on the ground below them.
Some swallows and flycatchers build mud nests attached to the sides of buildings, under culverts, and the eaves of houses.
Woodpeckers, wrens, some species of owls, sapsuckers, and swallows use cavities that they either excavate themselves or use after another has abandoned it. They will use holes found in live and dead trees, stumps, cacti, and sides of old buildings.
The types of nests that birds construct are as varied as the birds themselves. A few of the major examples are:
Scrape nests are simple depressions in the ground (sometimes with a few stones or leaves added), or in the leaf litter. Such nests are used by shorebirds, gulls, terns, nighthawks, vultures, and other species.
Burrow nests are very effective at protecting eggs and young from predators and maintaining an appropriate microclimate for eggs and young. Some birds, like Bank Swallows and Belted Kingfishers, usually construct their own burrows, while others, such as Burrowing Owls, may use the burrows constructed by other species.
Cavity nests are used by numerous passerines, woodpeckers, owls, parrots, and some waterfowl. Woodpeckers construct their own cavity nests and are referred to as primary cavity nesters. Species that use natural cavities or cavities constructed by primary cavity nesters are called secondary cavity nesters.
Platform nests are relatively flat nests that may be located on the ground, in a tree, or on the tops of rooted vegetation or debris in shallow water.
Cupped nests are, of course, cup shaped. Such nests may be constructed of various materials and in a variety of locations. Noted ornithologist Olin Sewall Pettingill subcategorized cup nests as follows:
Supported cupped nests: are those located in the crotches and branches of trees and shrubs, supported mainly from below. Many passerines and hummingbirds build such nests.
Suspended cupped nests: are not supported from below but from the rims, sides or both.
Pensile: nests are suspended from the rims and sides; rather stiff (e.g. those of kinglets and vireos).
Adherent nests: cupped nests whose sides are attached by an adhesive substance (e.g. mud or saliva) to a vertical surface, like those of swifts and some swallows.
Ground nests: include cupped nests on the ground; sides are sometimes extended upward and arched over the top making a domed structure. Several passerines, particularly those that occupy open habitats like grasslands, build ground nests. A local example is the White-crowned Sparrow.
Information on nests courtesy of Prof. Gary Ritchison, Ornithologist, Dept. of Biological Sciences Eastern Kentucky University – http://people.eku.edu/ritchisong/birdnests.html.