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A nest is a structure built by certain animals to hold their eggs or young. Although nests are most closely associated with , members of all classes of and some 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.
At the most basic level, there are only two types of nest building: sculpting and assembly.
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.
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 , 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 , , and many . The Ploceidae 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 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 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 , some (such as , , and many ) will build them on rocky ledges, and others nest on the ground or in . 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 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.
Many mammals, including and , 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. build their nests () in trees, while 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.
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.
use leaves and other debris to build nests in which they lay eggs that both sexes guard. They carry the vegetation to the nest site by kinking their necks. dig a hole in the sand above the high tide line in which they lay their eggs. They then cover the soft eggs to protect them from the sun and predators and leave.
The Oviraptor nests of Mongolia are perhaps the most famous case of dinosaur nesting. One specimen was found fossilized atop a nest in a brooding posture, proving the animal had been poorly named (Oviraptor means "egg taker").
A site known as Egg Mountain in Montana provides exceptional evidence of dinosaur nesting behavior. The site features dozens of nests each with 20 or more eggs belonging to the Maiasaura. Juvenile teeth at the site exhibit signs of wear, while the leg bones are not developed enough to walk. This allowed scientists to conclude that the species provided extensive parental care for its young. It is likely the species covered its nests with sand and vegetation to keep them warm and nested in colonies for increased protection.
Some types of bees and wasps (e.g., , , , ) often seek out natural cavities in which to construct their nests, in which they store food and raise their young. Most other species of bees and Aculeata, comprising thousands of solitary-nesting species, dig holes in the ground or burrow into wood or plant stems. In the solitary bee species Megachile rotundata, for example, females construct tubular-shaped nests in rotting wood as well as small holes in the ground, creating brood cells each containing pollen, nectar, and a single egg; each cell is made from pieces cut from plant leaves using the bee's mandibles. Honey bee and bumblebee nests are built using wax the workers secrete from their bodies, while those of various Vespidae wasps are dependent on their ability to turn plant fiber into paper using their saliva. Nests of highly social species often exhibit structural specialization, with eggs and food stores kept in distinct parts of the hive. Many vespid wasps build nests from paper, where they lay eggs in individual cells, and the wasp larvae are fed by the adults. Different species exhibit different nest structures. Paper wasp nests consist of a single tier of cells, while yellowjacket nests can be many layers thick. Nesting strategies can be plastic, for instance the wasp Parischnogaster mellyi will vary its nest construction based on environmental conditions, and the wasp Mischocyttarus mexicanus is known to nest in groups or alone depending on the distribution of potential nest sites in the area.Clouse, R. (2001). “Some effects of group size on the output of beginning nests of Mischocyttarus mexicanus (Hymenoptera: Vespidae).” Florida Entomologist. 84(3):418-424. Nest sizes vary dramatically and the largest wasp nest on record measured in diameter and was tall. Found in New Zealand, it was likely built by Vespula germanica, an invasive yellowjacket species.
The Eastern carpenter bee, Xylocopa virginica, builds nests in wood, bamboo culms, agave stalks, and other similar materials. When digging the nests, they use the wood shavings scraped from the wall to create partitions within the tunnels. The nest tunnels have about 1-4 branches, each with multiple brood cells. Because they will excavate nests in lumber used by humans in construction, their nesting behavior can weaken wood in manmade structures.Balduf, W. V. (1962-05-01). "Life of the Carpenter Bee, Xylocopa virginica (Linn.) (Xylocopidae, Hymenoptera)". Annals of the Entomological Society of America 55 (3): 263–271. doi:10.1093/aesa/55.3.263. ISSN 0013-8746.
Termites build elaborate nests that span multiple generations and may last decades. Using chewed wood, mud, and feces some species build large mounds which may extend well into the air. The largest nests, built by members of the genus Amitermes, stand nearly tall with a similar circumference at the base, and host millions of individuals. Termite mounds are constructed to allow for excellent air flow, regulating the mound temperature. The mounds protect against drying and predation allowing many species to lose ancestral traits such as hard bodies, pigmentation, and well-developed eyes. construct their nests with flattened sides along the north–south axis to ensure maximum warming during the winter, while exposing minimal surface area to the harshest mid-day sun. Other termite species use their nests to farm fungi.
Ant nests are often excavated in soil, and often feature an elaborate internal structure that may extend or more underground. As the structure gets further underground, individual chambers become farther and farther apart, but individual ants are bale to sense the level of carbon dioxide in the soil, and thus be aware of relative depth. build a complex nest which can, in some species, house 8 million individuals. The nests feature numerous chambers, most notably garden chambers where they farm fungus on leaves they harvest from the forest.
Species such as some and paper wasps (e.g. Polistes exclamans) build "satellite nests" - smaller nests near, but separate from, the main nest. These satellite nests are used as an insurance against predators and parasites; if the original nest is attacked, surviving members can move to the satellite nest. Other species such as Parischnogaster alternata, construct nests in clusters with the central core composed of older colonies surrounded by younger colonies.Landi, M., C. Coster-Longman, and S. Turillazzi. "Are the Selfish Herd and the Dilution Effects Important in Promoting Nest Clustering in the Hover Wasp (Stenogastrinae Vespidae Hymenoptera)?" Ethology Ecology & Evolution 14.4 (2002): 297-305. Web.
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