Bird nests are a spot in which a bird lays and incubates its eggs. Not all birds build nests, some species lay their eggs directly on the ground or rocky ledges while brood parasites lay their eggs in the nests of other birds. This includes the cow bird which will lay its eggs in the nests of other species, some of which recognize the egg and remove it from the nest while others raise it as one of their own. If a cowbird lays its egg in the nest of a yellow warbler, the warbler will build another nest on top of the previous one and will build up to six nests on top of each other. Most birds build a new nest each year although some refurbish nests from previous years. In most species the female does most or all of the nest construction.
There are a couple different types of nests. One is called a scrape nest which is just a shallow depression in the soil or vegetation that has a rim just deep enough to keep the eggs from rolling away. The nests are commonly lined with bits of vegetation, small stones, shell fragments or feathers to help camouflage the eggs, provide insulation or to keep them from sinking into muddy or sandy soil if the nest is accidentally flooded.
Another type of nest is a burrow. In this type of nest the eggs and young and in most cases the incubating parent are sheltered in the earth. Most use their own burrows but some use those excavated by others. Burrow nests are common among seabirds at high latitudes as they provide protection against cold and predators.
Some birds like to nest in cavities in living or dead wood. A relatively small number of birds, called primary cavity nesters can excavate their own holes. Most species use natural holes or those excavated by other species and these are called secondary cavity nesters. Both can be convinced to use nest boxes and sometimes they are critical to the species survival.
Furthermore there is a nest type called a cup which has a deep depression inside to house the eggs. Most are made of pliable materials including grasses though a small number are made of mud or saliva. Small birds even use a large amount of spider silk in the construction of their nests.
There are also platform nests which are large structures often many times the size of the bird which has built it. Depending on the species the nests can be on the ground or elevated up in a tree. In extreme cases the nests grow large enough to cause structural damage to the tree it is located in.
Finally, there are pendant nests which are elongated sacs woven out of pliable material such as grasses and plant fibers and suspended from a branch. Birds such as Orioles prefer to live in pendant nests.
Most species of birds nest individually but some species prefer to nest all together like the Great Blue Heron. By doing so they can benefit from increased protection from predators and may be able to utilize food supplies better by following more successful foragers to their foraging sites.
– V. Nolan (2014)
