Not every bird species builds or uses a nest. Some
auks, for instance—including
common murre,
thick-billed murre and
razorbill—lay their eggs directly onto the narrow rocky ledges they use as breeding sites. The eggs of these species are dramatically pointed at one end, so that they roll in a circle when disturbed. This is critical for the survival of the developing eggs, as there are no nests to keep them from rolling off the side of the cliff. Presumably because of the vulnerability of their unprotected eggs, parent birds of these auk species rarely leave them unattended. Nest location and architecture is strongly influenced by local topography and other abiotic factors.
King penguins and
emperor penguins also do not build nests; instead, they tuck their eggs and chicks between their feet and folds of skin on their lower bellies. They are thus able to move about while incubating, though in practice only the emperor penguin regularly does so. Emperor penguins breed during the harshest months of the
Antarctic winter, and their mobility allows them to form huge huddled masses which help them to withstand the extremely high winds and low temperatures of the season. Without the ability to share body heat (temperatures in the centre of tight groups can be as much as 10C above the ambient air temperature), the penguins would expend far more energy trying to stay warm, and breeding attempts would probably fail. Some crevice-nesting species, including
ashy storm-petrel,
pigeon guillemot,
Eurasian eagle-owl and
Hume's tawny owl, lay their eggs in the relative shelter of a crevice in the rocks or a gap between boulders, but provide no additional nest material.
Potoos lay their single egg directly atop a broken stump, or into a shallow depression on a branch—typically where an upward-pointing branch died and fell off, leaving a small scar or knot-hole.
Brood parasites, such as the
New World cowbirds, the
honeyguides, and many of the
Old World and
Australasian
cuckoos, lay their eggs in the active nests of other species.
Scrape ''
plover scrape, may help to prevent the eggs from sinking into muddy or sandy soil. The simplest nest construction is the
scrape, which is merely a shallow depression in soil or vegetation. This nest type, which typically has a rim deep enough to keep the eggs from rolling away, is sometimes lined with bits of vegetation, small
stones,
shell fragments or
feathers. These materials may help to camouflage the eggs or may provide some level of insulation; they may also help to keep the eggs in place, and prevent them from sinking into muddy or sandy soil if the nest is accidentally flooded. Ostriches, most
tinamous, many ducks, most
shorebirds, most
terns, some
falcons,
pheasants,
quail,
partridges,
bustards and
sandgrouse are among the species that build scrape nests. Eggs and young in scrape nests, and the adults that brood them, are more exposed to
predators and the
elements than those in more sheltered nests; they are on the ground and typically in the open, with little to hide them. The eggs of most ground-nesting birds (including those that use scrape nests) are cryptically coloured to help camouflage them when the adult is not covering them; the actual colour generally corresponds to the substrate on which they are laid. Brooding adults also tend to be well camouflaged, and may be difficult to flush from the nest. Most ground-nesting species have well-developed
distraction displays, which are used to draw (or drive) potential predators from the area around the nest. Most species with this type of nest have
precocial young, which quickly leave the nest upon hatching. nest-scraping on artificial ledge on
Derby Cathedral. Both sexes contribute to the creation of a bare, shallow depression in soil or gravel. In cool climates (such as in the high
Arctic or at high elevations), the depth of a scrape nest can be critical to both the survival of developing eggs and the fitness of the parent bird incubating them. The scrape must be deep enough that eggs are protected from the
convective cooling caused by cold winds, but shallow enough that they and the parent bird are not too exposed to the cooling influences of ground temperatures, particularly where the
permafrost layer rises to mere centimeters below the nest. Studies have shown that an egg within a scrape nest loses heat 9% more slowly than an egg placed on the ground beside the nest; in such a nest lined with natural vegetation, heat loss is reduced by an additional 25%. The insulating factor of nest lining is apparently so critical to egg survival that some species, including
Kentish plovers, will restore experimentally altered levels of insulation to their pre-adjustment levels (adding or subtracting material as necessary) within 24 hours. in this
American golden-plover scrape, may provide some level of insulation for the eggs, or may help to camouflage them. In warm climates, such as
deserts and
salt flats, heat rather than cold can kill the developing embryos. In such places, scrapes are shallower and tend to be lined with non-vegetative material (including shells, feathers, sticks and soil), which allows convective cooling to occur as air moves over the eggs. Some species, such as the
lesser nighthawk and the
red-tailed tropicbird, help reduce the nest's temperature by placing it in partial or full shade. Others, including some shorebirds, cast shade with their bodies as they stand over their eggs. Some shorebirds also soak their breast feathers with water and then sit on the eggs, providing moisture to enable
evaporative cooling. Parent birds keep from overheating themselves by
gular fluttering while they are incubating, frequently exchanging incubation duties, and standing in water when they are not incubating. The technique used to construct a scrape nest varies slightly depending on the species. Beach-nesting terns, for instance, fashion their nests by rocking their bodies on the
sand in the place they have chosen to site their nest, while
skimmers build their scrapes with their feet, kicking sand backwards while resting on their bellies and turning slowly in circles. The ostrich also scratches out its scrape with its feet, though it stands while doing so. Many tinamous lay their eggs on a shallow mat of dead
leaves they have collected and placed under
bushes or between the
root buttresses of trees, and
kagus lay theirs on a pile of dead leaves against a log, tree trunk or vegetation.
Marbled godwits stomp a grassy area flat with their feet, then lay their eggs, while other grass-nesting waders bend vegetation over their nests so as to avoid detection from above. Many female ducks, particularly in the northern
latitudes, line their shallow scrape nests with
down feathers plucked from their own breasts, as well as with small amounts of vegetation. Among scrape-nesting birds, the
three-banded courser and
Egyptian plover are unique in their habit of partially burying their eggs in the sand of their scrapes.
Mound acts like a compost heap, warming and incubating the eggs as it rots around them.|thumb|right Burying eggs as a form of incubation reaches its zenith with the
Australasian
megapodes. Several megapode species construct enormous
mound nests made of soil, branches, sticks, twigs and leaves, and lay their eggs within the rotting mass. The heat generated by these mounds, which are in effect giant
compost heaps, warms and incubates the eggs.—were initially thought to be
Aboriginal middens. In most mound-building species, males do most or all of the nest construction and maintenance. Using his strong legs and feet, the male scrapes together material from the area around his chosen nest site, gradually building a
conical or bell-shaped pile. This process can take five to seven hours a day for more than a month. While mounds are typically reused for multiple breeding seasons, new material must be added each year to generate the appropriate amount of heat. A female will begin to lay eggs in the nest only when the mound's temperature has reached an optimal level. s, help to protect their eggs from fluctuating water levels. Both the temperature and the moisture content of the mound are critical to the survival and development of the eggs, so both are carefully regulated for the entire length of the breeding season (which may last for as long as eight months), principally by the male. If the mound's core temperature is a bit low, he adds fresh moist material to the mound, and stirs it in; if it is too high, he opens the top of the mound to allow some of the excess heat to escape. This regular monitoring also keeps the mound's material from becoming compacted, which would inhibit oxygen diffusion to the eggs and make it more difficult for the chicks to emerge after hatching. One recent study showed that the sex ratio of
Australian brushturkey hatchlings correlated strongly with mound temperatures; females hatched from eggs incubated at higher mean temperatures.
Flamingos make a different type of mound nest. Using their
beaks to pull material towards them, they fashion a cone-shaped pile of mud between tall, with a small depression in the top to house their single egg. The height of the nest varies with the substrate upon which it is built; those on
clay sites are taller on average than those on dry or sandy sites.
Burrow s dig a horizontal tunnel into a vertical dirt cliff. Soil plays a different role in the
burrow nest; here, the eggs and young—and in most cases the incubating parent bird—are sheltered under the earth. Most burrow-nesting birds excavate their own burrows, but some use those excavated by other species and are known as secondary nesters;
burrowing owls, for example, sometimes use the burrows of
prairie dogs,
ground squirrels,
badgers or
tortoises, China's endemic
white-browed tits use the holes of ground-nesting rodents and
common kingfishers occasionally nest in rabbit burrows. Burrow nests are particularly common among seabirds at high latitudes, as they provide protection against both cold temperatures and predators.
Puffins,
shearwaters, some megapodes,
motmots,
todies, most
kingfishers, the
crab plover,
miners and
leaftossers are among the species which use burrow nests. Most burrow nesting species dig a horizontal tunnel into a vertical (or nearly vertical) dirt cliff, with a chamber at the tunnel's end to house the eggs. The length of the tunnel varies depending on the substrate and the species;
sand martins make relatively short tunnels ranging from , for example, while those of the
burrowing parakeet can extend for more than three meters (nearly 10 ft). Some species, including the ground-nesting
puffbirds, prefer flat or gently sloping land, digging their entrance tunnels into the ground at an angle. In a more extreme example, the
D'Arnaud's barbet digs a vertical tunnel shaft more than a meter (39 in) deep, with its nest chamber excavated off to the side at some height above the shaft's bottom; this arrangement helps to keep the nest from being flooded during heavy rain.
Buff-breasted paradise-kingfishers dig their nests into the compacted mud of active termite mounds, either on the ground or in trees. , to become colonial breeders. Birds use a combination of their beaks and feet to excavate burrow nests. The tunnel is started with the beak; the bird either probes at the ground to create a depression, or flies toward its chosen nest site on a cliff wall and hits it with its bill. The latter method is not without its dangers; there are reports of kingfishers being fatally injured in such attempts. Sand martins learn the location of their nest within a colony, and will accept any chick put into that nest until right before the young
fledge. Not all burrow-nesting species incubate their young directly. Some megapode species, such as the
maleo, bury their eggs in sandy pits dug where sunlight, subterranean volcanic activity, or decaying tree roots will warm the eggs. Predation levels on some burrow-nesting species can be quite high; on
Alaska's Wooded Islands, for example,
river otters munched their way through some 23 percent of the island's
fork-tailed storm-petrel population during a single breeding season in 1977. There is some evidence that increased vulnerability may lead some burrow-nesting species to form colonies, or to nest closer to rival pairs in areas of high predation than they might otherwise do.
Cavity , use natural cavities or holes excavated by other species. The
cavity nest is a chamber, typically in living or dead wood, but sometimes in the trunks of
tree ferns or large
cacti, including
saguaro. A relatively small number of species, including
woodpeckers,
trogons, some
nuthatches and many
barbets, can excavate their own cavities. Far more species—including
parrots,
tits,
bluebirds, most
hornbills, some kingfishers, some
owls, some ducks and some flycatchers—use natural cavities, or those abandoned by species able to excavate them; they also sometimes usurp cavity nests from their excavating owners. Those species that excavate their own cavities are known as "primary cavity nesters", while those that use natural cavities or those excavated by other species are called "secondary cavity nesters". Both primary and secondary cavity nesters can be enticed to use
nest boxes (also known as bird houses); these mimic natural cavities, and can be critical to the survival of species in areas where natural cavities are lacking. Woodpeckers use their chisel-like bills to excavate their cavity nests, a process which takes, on average, about two weeks. Cavities are normally excavated on the downward-facing side of a branch, presumably to make it more difficult for predators to access the nest, and to reduce the chance that rain floods the nest. There is also some evidence that fungal rot may make the wood on the underside of leaning trunks and branches easier to excavate. While some species appear to preferentially choose holes with certain orientations, studies (to date) have not shown consistent differences in fledging rates between nests oriented in different directions. They have a variety of methods for decreasing the likelihood of this happening. Red-cockaded woodpeckers peel bark around the entrance, and drill wells above and below the hole; since they nest in live trees, the resulting flow of resin forms a barrier that prevents snakes from reaching the nests.
Red-breasted nuthatches smear sap around the entrance holes to their nests, while
white-breasted nuthatches rub foul-smelling insects around theirs.
Eurasian nuthatches wall up part of their entrance holes with mud, decreasing the size and sometimes extending the tunnel part of the chamber. Most female hornbills seal themselves into their cavity nests, using a combination of mud (in some species brought by their mates), food remains and their own droppings to reduce the entrance hole to a narrow slit. A few birds are known to use the nests of insects within which they create a cavity in which they lay their eggs. These include the
rufous woodpecker which nests in the arboreal nests of
Crematogaster ants and the
collared kingfisher which uses termite nests. In December 2024, scientists reported that birds that build their nests in cavities are more than six times more likely to incorporate snakeskin into their nests than those which build cup-shaped nests. The same study found that the snake skin helped deter predators from eggs during their incubation period.
Cup uses considerable amounts of
spider silk in its cup nest. The
cup nest is smoothly hemispherical inside, with a deep depression to house the eggs. Most are made of pliable materials—including grasses—though a small number are made of
mud or
saliva. Many
passerines and a few non-passerines, including some
hummingbirds and some
swifts, build this type of nest. Small bird species in more than 20 passerine families, and a few non-passerines—including most hummingbirds, kinglets and crests in the genus
Regulus, some
tyrant flycatchers and several
New World warblers—use considerable amounts of
spider silk in the construction of their nests. The lightweight material is strong and extremely flexible, allowing the nest to mold to the adult during incubation (reducing heat loss), then to stretch to accommodate the growing nestlings; as it is sticky, it also helps to bind the nest to the branch or
leaf to which it is attached. nest wall thickness, nest depth, surface area, In the case of raptor nests, or
eyries (also spelled
aerie), these are often used for many years, with new material added each breeding season. In some cases, the nests grow large enough to cause structural damage to the tree itself, particularly during bad storms where the weight of the nest can cause additional stress on wind-tossed branches.
Pendent building pendent nest. The
pendent nest is an elongated sac woven of pliable materials such as grasses and plant fibers and suspended from a branch.
Oropendolas,
caciques,
orioles,
weavers and
sunbirds are among the species that weave pendent nests. In weaver birds, the nest is suspended from a single point on a branch, while other birds incorporate more than one branch to support the nest. carrying fibers and constructing a hanging nest (left)
Sphere The
sphere nest is a roundish structure; it is completely enclosed, except for a small opening which allows access. Most spherical nests are woven out of plant material. Spider webs are also frequently used, upon which other material such as lichens may be stuck for camouflage. The
cape penduline tit incorporates false entrances, the parent bird carefully making sure to close the actual entrance when leaving the nest. The entrances are lined with spider webs which help seal the openings. ==Nest protection and sanitation==