Architects of The Air

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Published on: Mar. 2, 1999

Last revision: Nov. 3, 2010

woodpecker's nest usually faces south or east. For the downy woodpecker, it seems important that the entrance be on the underside of a limb.

Wrens, chickadees, titmice and many owls also are cavity nesters. They line the nest cavity with soft grasses, feathers or fur. Tufted titmice and great crested flycatchers add cast-off snakeskin to their nests, which may scare away predators.

Though some of these birds will excavate their own holes, most prefer to use holes abandoned by other birds. In recent years, bluebirds have benefited from the proliferation of bird houses built to suit them. These artificial cavities have helped increase the once declining population of Missouri's state bird.

Purple martins take readily to colony houses set out for them. They add green leaves to their nests. The leaves can help regulate humidity and may emit a natural fumigant to control lice.

Some cavity nesters don't rely on trees or houses to raise their brood. Belted kingfishers dig a cavity into a stream bank. Both partners participate in the excavation, and they often return to the same nest in subsequent years. The first clutch is laid directly on the dirt floor, but subsequent clutches usually rest on fish scales and other debris from past feedings.

Cavity nesters have a higher success rate raising their broods than open nesters, but the open nesters compensate by tending to have more broods in the season.

And then there are birds that don't bother with nest building at all. A cowbird will lay her eggs in the nest of another species, leaving incubation and rearing to the adoptive parents.

Killdeer just use a scrape on the ground for their nest. They may line it with gravel, wood chips or other debris, but they rely on the mottled coloring of the eggs to hide them. Killdeer parents often feign a broken wing to draw predators away from their nest.

Turkeys make minimal nests. A hen scratches out a small depression in leaf litter, often near a fallen log, to lay her eggs. While she is brooding, she sometimes draws leaves over her back. When she gets up, the leaves fall on the eggs and conceal them until her return.

Birds that make virtually no nest tend to produce young that are mobile within hours of hatching. The young of some species, such as bobwhite quail, may fly within a week.

Not all ground nesters produce mobile young. Turkey vultures lay their eggs on the bare ground and must tend to their young for as long as three months before they are able to fly. Nor do all ground nesters forsake a nest. The females of both Canada geese and mallards build nests on the ground, usually in dense vegetation, though geese readily build in washtubs set out for them. Both birds line their nests with grass, cattails and reeds, eventually adding down from their own breasts.

The female ovenbird builds her nest among the leaves of grasses, moss and even root fibers. Its arched top made of leaves and surrounding plants completely hides it from predators above. Female meadowlarks build similar nests.

The spring frenzy of nest building is fascinating. Birds are especially active, and their comings and going for nest materials can lead you to their building sites. Yet nests should be left undisturbed during nesting season. Poking around too close may keep the birds from their nests or cause them to abandon them. Eggs left unattended for even a few minutes can die.

One of the best times to find nests is in the winter, when leaves are gone and you can spot most silhouettes in the trees. An area with several nests suggests that the site is favorable to birds, and they likely will return to it in the spring.

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