Nest
A nest is a structure built by certain animals to hold their eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic material such as twigs, grass, and leaves, or may be a simple depression in the ground, or a hole in a rock, tree, or building. Human-made materials, such as string, plastic, cloth, or paper, may also be used. Nests can be found in all types of habitat.
Nest building is driven by a biological urge known as the nesting instinct in birds and mammals. Generally each species has a distinctive style of nest. Nest complexity is roughly correlated with the level of parental care by adults. Nest building is considered a key adaptive advantage among birds, and they exhibit the most variation in their nests ranging from simple holes in the ground to elaborate communal nests hosting hundreds of individuals. Nests of prairie dogs and several social insects can host millions of individuals.
Nest building
Purposes of nesting
Structural purposes
Nest building is often driven by a biological urge in pregnant animals to protect one's offspring known as the nesting instinct. Animals build nests to protect their eggs, their offspring, or themselves from danger. The simplest nest structures are adapted to hide eggs from predators, shield them from the sun or other environmental factors, or simply keep them from being scattered in ocean currents. In some cases, nests also help provide safety in numbers for egg-laying animals.Social purposes
Many nest builders provide parental care to their young, while others simply lay their eggs and leave. Brooding is common among birds. In general, nest complexity increases in relation to the level of parental care provided. Nest building reinforces social behavior, allowing for larger populations in small spaces to the point of increasing the carrying capacity of an environment. Insects that exhibit the most complex nidification also exhibit the greatest social structure. Among mammals, the naked mole-rat displays a caste structure similar to the social insects while building extensive burrows that house hundreds of individuals.Usage of environment
Versatility in use of construction material may be an adaptive advantage or a disadvantage. The available evidence suggests that natural selection more often favors specialization over flexibility in nest construction.At the most basic level, there are only two types of nest building: sculpting and assembly.
Sculpting
Sculpting is the process of removing material to achieve the desired outcome. Most commonly this entails burrowing into the ground or plant matter to create a nesting site.Assembly
Assembly entails gathering, transporting, and arranging materials to create a novel structure. Transportation has the greatest time and energy cost so animals are usually adapted to build with materials available in their immediate environment.Building materials
is the most common construction material for nests. Other common materials include fur or feathers, perhaps from the animal itself, mud or dirt, fecal matter, and specialized secretions from the animal's body.Effects on environment
Nest building can have a substantial impact on the environment in which animals live. The combined digging activity of termites and mole-rats in South Africa has created a "mima prairie" landscape marked by huge areas of flat land punctuated by mounds wide and high. Similar structures exist in the United States, created by pocket gophers, and Argentina, rodents of the genus Ctenomys.Lasting effects
Nests constructed by megapode birds have been mistaken for anthropological features by professionals, due to their exceptional height and abundance.Some nests, such as those built by bearded vultures, can last for several centuries, after being used by multiple generations of birds. In one of such nests, several human objects from the 13th to the 19th centuries were found, all of them in the same nest.
Nest builders
Nest architecture may be as useful for distinguishing species as the animals' physical appearance. Species identified through such means are called ethospecies. This is especially common in wasps and termites, but also can apply to birds. In most animals, there is some variation in nest construction between individuals. Whether these differences are driven by genetics or learned behavior is unknown.With the exception of a few tunneling mammals, nest builders exhibit no specialized anatomy, instead making use of body parts primarily used for other purposes. This is possibly due to the sporadic nature of nest building, minimizing the selective pressures of anatomy used for nest building.
Birds
In general, birds are the most skilled nest builders, although not all species of birds build nests, some laying their eggs directly onto rock ledges or bare soil without first modifying the area. Complex nest building is considered to be one of the key adaptive advantages of birds. Nests help regulate temperature and reduce predation risks, thus increasing the chance that offspring live to adulthood.Bird nests vary from simple depressions in the ground known as scrapes to largely unstructured collections of branches to elaborately woven pendants or spheres. The megapodes, one of the few groups who do not directly brood their young, incubate their young in a mound of decomposing vegetation. One species, Macrocephalon maleo, uses volcanic sand warmed by geothermal heat to keep its eggs warm. Among the simple nest builders are falcons, owls, and many shorebirds. The weavers exhibit perhaps the most elaborate nests, complete with strands of grass tied into knots. Most bird nests lie somewhere in the middle, with the majority building cup-shaped nests using some combination of mud, twigs and leaves, and feathers. Some birds, such flamingos and swifts, use saliva to help hold their nest together. The edible-nest swiftlet uses saliva alone to construct their nests. The rufous hornero nest is composed entirely of mud and feces, which is placed on tree branches to allow the sun to harden it into a usable structure. The tailorbirds stitch together leaves to provide cover for their nest sites.
The sociable weaver builds large communal nests in which many individual nests reside. They divide the nest using walls of grass placed atop a base of large sticks. At the entrances to the nest, sharp sticks are placed to ward off intruders. A single communal site can measure in height and in width. As many as 300 mating pairs may reside in the structure. Other birds often built their own nests on top of Weaver nest sites.
Some birds build nests in trees, some will build them on rocky ledges, and others nest on the ground or in burrows. Each species has a characteristic nest style, but few are particular about where they build their nests. Most species will choose whatever site in their environment best protects their nest, taking into account the nest's style. Several species will build on a cactus whenever possible. The bushtit and Bullock's oriole will suspend their nests from the tips of slender branches. The oropendolas take hanging nests to the extreme, constructing pouches up to tall using hanging vines as their base. The hanging nest is attached to thin tree branches, discouraging predation. Other species seek out crevices, using buildings or birdhouses when tree holes are not available.
Typical bird nests range from in size to in diameter. The largest nest on record was made by a pair of bald eagles. It was in diameter, deep and was estimated to weigh more than. The lightest bird nests may weigh only a few grams. Incubation mounds of the mallee fowl can reach heights of and widths of. It is estimated the animal uses as much as of material in its construction. The extinct Sylviornis neocaledoniae may have constructed nesting mounds in diameter.
Mammals
Many species of small mammals such as rodents, rabbits, and ground squirrels dig burrows into the ground to protect themselves and their young. Prairie dogs build an elaborate system of tunnels which can span large stretches of land. One such structure, called a town, spanned and held an estimated 400 million individuals. Their homes are adapted to withstand large temperature variation, floods, and fire. Their young are raised in the deepest chambers where the temperature is the most stable.Many mammals, including raccoons and skunks, seek natural cavities in the ground or in trees to build their nests. Raccoons, and some rodents, use leaves to build nests underground and in trees. Tree squirrels build their nests in trees, while voles nest in tall grass. In some species, the nest serve as homes for adults while in others they are used to raise young. The duck-billed platypus and the echidna lay eggs in nests.
Gorillas build fresh nests daily out of leaves and other vegetation in which they sleep at night. They sometimes also build nests during the day for resting in. The smaller species of gorilla build their nests in trees, while the larger are confined to the ground. Nests of the western gorilla, the largest species, measure about in diameter.