Nesting

Many animals build structures to house and protect themselves, their eggs, and their young. Nest sites include grasses, shrubs, and trees, but also cracks in trees, holes in the ground and banks, crevices in rocks, under the ground's surface, within the nests of other larger animals, or even near wasp nests. The nests of birds are the most obvious and well-known, but many amphibians, reptiles, fishes, social insects, and mammals also build nests of varying degrees of complexity and permanence.

Bird and Insect Nests

Larger bird nests are constructed of various kinds of material, such as mud, bark, roots, twigs, hair, feathers, grass, plant fibers, shed snake skin, spider webs, lichens, or even prey remains and human-made material such as shiny, light, metallic ornaments. Many nests are cup-shaped and open, while fewer are oval, round or ball-shaped, closed, with an entrance at the side or the roof. An example of the latter is the nest of the South American ovenbird (Furnarius), which is often built with mud on top of a fence or another exposed surface. Others build a domed, oven-shaped nest out of plant material (the North American ovenbird) or huge nests suspended from the ends of tree branches (thorn birds). Some oceanic gulls, like the black-legged kittiwake (Rissa tridactyla), nest on narrow cliff ledges. Grassland and tundraowls nest on the ground or on an elevated hummock.

Some birds utilize amazing skills to construct their nests. The weavers are capable of tying knots with strips of grass or palm leaves and can prepare an exceptionally tight and compact nest. All weaver species create roofed nests. Some weaver nests are intricately woven round chambers that hang from trees, which helps protect the birds and eggs from snakes. Males build these nests, and the best nests attract the best mates. Birds of the genus Orthotomus are known as tailorbirds due to their ability to manufacture nests that are built in a pocket by sewing together the edges of one or more leaves using plant fibers. Some others (the family Cotingidae) prepare very primitive and weak nests in an apparent effort to avoid the attention of predators since they are attended minimally by the parents. Finally, woodcreepers nest in holes, while vireos weave a cup between the arms of a forked branch.

Most bird species in an area construct a unique nest in a unique location but use specific construction materials transferred from a distance. Generally, female geese and robins build their own nests, but among several other species, the nest is built only by the male, who may use it as a sexual attractant in courtship. In these species, the female chooses a nest and indicates her choice by adding the nest lining.

Woodpeckers create cavities in trees, thus supplying safe nesting sites for many birds. These include owls, parrots, parids, and flycatchers. In some areas, forest managers protect pileated woodpecker cavity trees and employ strategies to encourage continued production of new cavity trees where even smaller woodpecker species may find a haven for nesting.

Social insects, such as wasps, ants, termites, and carpenter bees, excavate a tunnel through solid wood, dirt, and mud. Many wasp species build hanging nests by chewing wood and using it like clay, while around 70 percent of bees nest in the ground. When termite colonies accidentally separate from an original nest, they may migrate or march to a new nesting site and develop supplementary reproductives. Many species of social insects build a complex nest, and the group remains there for years if it is not destroyed.

Mammal Nests

Most rodents build underground residences with a central chamber, where they sleep, raise their young, and hibernate, and other chambers that serve as food storage quarters. Moles build the most complex shelters among all insectivores. The shelters have an underground nest chamber that is surrounded by concentric rings of tunnels that are interconnected by radiating ones. The presence of shallow surface tunnels allows the marking of their course, and the accumulation of a large amount of earth indicates the location of the deep tunnel system. The mole uses its forefeet like a shovel to dig in a type of body movement that resembles that of a breaststroke swimmer. Shrews dig surface nests, but they also use the runs of other animals, such as rodents, and line them with plant material on which they place their offspring. Hedgehogs and solenodons construct nest chambers, usually during their breeding season, which warm them during low-temperature periods. Tree shrews build their nests of leaves and other vegetation among tree roots or in cavities of fallen timber, but they immediately desert them when they feel that their residence has been stalked or even detected by a predator. The largest nesting mammal is the gorilla, which builds a new nest on the ground each day.

Ground squirrels and kangaroo rats transport enough seeds and other food in their cheek pouches to last them for a whole season. Excavation of one rat den where a single five-ounce kangaroo rat resided produced nine underground storage chambers with a total of thirty-five quarts of seeds. Kangaroo rats also dig one-cubic-inch storage pits that they stuff with seeds. In one case, an area of fifty-five square feet adjacent to a den had close to nine hundred such pits. This can have a devastating effect on local crops, so-called rodent plagues. On the other hand, such underground activity tends to germinate seeds for wild grass in the arid steppe regions of Central Asia. Squirrels carry acorns and nuts to hollow trees and barns, as well as to holes in the ground. They also have an amazing memory of where the food is stored, which keeps them alive during the harsh winter. Finally, the North American pack rat or trade rat is attracted by bright, shining objects (like the magpie) and carries them home to its nest, where it stores them together with tree sticks and grass.

Cooperative breeding appears to exist in the form of communal nesting among several mammal species. American tree squirrels (tribe sciurini), fox squirrels (Sciurus niger), and eastern gray squirrels (Sciurus carolinensis) form kin clusters among unrelated members of their own species during all seasons, especially in winter. Gray squirrels have shown an intense female-female bond in the formation of groups. Fox and gray squirrels build nests out of leaves called dreys high in the trees.

Artificial Nesting

Humans living in suburban and rural areas can provide the appropriate housing for cavity-nesting birds, and people do have the ability to become backyard bird specialists. Artificial structures have been used extensively in the United States and Canada to increase waterfowl production, although the users of the artificial materials are not always the animals for which they were intended. During a study in which artificial nesting structures were intended for mallard use, redheads were found to be using them for normal nesting. It is believed that a combination of elevated water surfaces and subsequent limited nesting in the emergent vegetation may have made these nesting sites attractive to the redheads, which has thus provided a new alternative for nesting redheads. European starlings are cavity-nesting birds prevalent throughout North America and they often use dryer or exhaust fan vents to make their nests.

Another study on the excavation and use of artificial polystyrene snags by woodpeckers was performed in Eastern Texas over a period of five years in the early 1990s. Only half of the monitored downy woodpeckers (Picoides pubescens) appeared to use the artificial snags for cavity excavation and later for nocturnal roosting, but not for nesting. None of the other six woodpecker species in the area excavated cavities in the artificial snags. Other animals, however, used these excavated cavities in the artificial snags. These include Carolina chickadees (Poecile carolinensis), prothonotary warblers (Protonotaria citrea), southern flying squirrels (Glaucomys volans), and red paper wasps (Polistes carolina).

The human factor may directly or indirectly affect the breeding success of animals. Possible biological effects of electromagnetic fields attributed to high-voltage transmission lines are suspected to reduce the reproductive success of birds whose nests are nearby, as in the case of tree swallows. Similar effects have been postulated for the terns, gulls, and other birds that live in areas such as the Gulf Coast, where oil tankers, commercial fishing vessels, yachts, and other pleasure boats have degraded the environment. Controversy occurred in the 1990s in the Pacific Northwest of the United States, where environmentalists lobbied for the preservation of the nesting habitat of the spotted owl to the detriment of the local logging industry. Further disturbances continued with the advent of drones, which may cause animals to abandon their nests, lay fewer eggs, or not build nests in their typical area. However, if scientists use an appropriate altitude with a high-quality camera and consider the needs of the species they are studying, drones can be a useful tool for conservation, population estimations, and other research. Additionally, humans' contribution to climate change negatively impacts nesting animals. For example, research indicates that birds began nesting earlier each spring in the first decades of the twenty-first century.

Principal Terms

Insectivore: any animal that feeds on insects

Mallard: a species of wild duck

Ornithology: the scientific study of birds

Pheromones: chemicals excreted by animals into their immediate environments to identify their territorial influence on other organisms

Territorial Behavior: the combination of methods and actions through which an animal or group of animals protects its territory from invasion by other species

Territory: any area defended by an organism or a group of organisms for purposes such as mating, nesting, roosting, or feeding

Bibliography

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