Burrow


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Burrow


	[Scrape] [Mound] [Burrow] [Cavity] [Cup]

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; 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. 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 50–90 cm (20–35 in), 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.

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. Some birds remove tunnel material with their bills, while others use their bodies or shovel the dirt out with one or both feet. Female paradise-kingfishers are known to use their long tails to clear the loose soil.

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.

Some petrels and prions that are crepuscular are able to identify their home burrows within dense colonies of nesting burrows by their specific nest odours.

Not all burrow-nesting species incubate their young directly. Some megapode species bury their eggs in sandy pits dug where sunlight, subterranean volcanic activity, or decaying tree roots will warm the eggs. The Crab Plover similarly makes use of a burrow nest, the warmth of which allows it to forage away from the nest.