Without the ability to share body heat (temperatures in the center 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. 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. They are thus able to move about while incubating, though in practice only the Emperor Penguin regularly does so.
King 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. Presumably because of the vulnerability of their unprotected eggs, parent birds of these auk species rarely leave them unattended. 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. The eggs of these species are dramatically pointed at one end, so that they roll in a circle when disturbed. 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. Not every bird species builds or uses a nest. Thick-billed Murres ( Uria lomvia) lay their single eggs directly onto rock ledges In some species the young from previous broods may also act as helpers for the adults. The ability to choose and maintain good nest sites and build high quality nests may be selected for by females in these species. The nest may also form a part of their courtship display such as in bowerbirds and weaver birds. In some polygynous species, however, the male may do most or all of the nest building. In most species, the female does all or most of the nest construction, though the male often helps. At the other extreme, some nest mounds built by the Dusky Scrubfowl measure more than 11 m (34 ft) in diameter and stand nearly 5 m (15 ft) tall. The smallest bird nests are those of some hummingbirds, tiny cups which can be a mere 2 cm (less than one inch) across and 2–3 cm (about one inch) high. Some species of cave swiftlets of the genus Collocalia make their nests entirely from their saliva which dries and hardens to form a bracket on the cave wall into which the birds lay their eggs. For some species, a nest is simply a shallow depression made in sand for others, it is a burrow dug into the ground, a chamber drilled into a tree, an enormous rotting pile of vegetation and earth, or a mud dome with an entrance tunnel. While the term popularly refers to a specific structure made by the bird itself-such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the Montezuma Oropendola, the Village Weaver or the Red-browed Pardalote-that is too restrictive a definition. Deep cup nest of the Great Reed-warbler ( Acrocephalus arundinaceus)Ī bird nest is the spot in which a bird lays and incubates its eggs and raises its young.