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Wildlife: Some birds dig burrow nests

Sunday, August 03, 2003

By Scott Shalaway

A hole in the ground may seem a strange place to find a bird nest, but underground burrows are home to a surprising variety of birds. For example, the holes you may have seen in sandy stream banks this summer could have been the nesting burrow of a belted kingfisher or one of two burrow-nesting species of swallows.

The idea that free-flying birds willfully enter underground tunnels to nest has always struck me as odd. But just like tree cavities, burrows provide secure nesting quarters for birds able to use them. The actual nest is relatively inaccessible, remains hidden from predators and is well protected from rain and high winds. Perhaps that's why it's a habit that's seen worldwide.

 
 

Send questions and comments to Dr. Scott Shalaway, R.D. 5, Cameron, WV 26033 or via e-mail to sshalaway@aol.com, and catch Scott on the radio Saturday afternoons from 2 to 4 p.m. on 1360 WPTT.

   
 

As you might expect, some relatives of woodpeckers use underground burrows. These include puffbirds and jacamars in South America, and barbets in tropical zones.

In New Zealand, the primitive and flightless kiwi lays one or two large eggs in an underground burrow. Each egg weighs about one pound, a mighty effort for a bird that weighs no more than nine pounds itself.

Representatives from five families of seabirds also raise their young in burrows. Most are awkward on land and come there only to nest, often after spending several years at sea before reaching sexual maturity. Perhaps being able to fly directly to a nest burrow and disappear underground is a behavior that makes the nest site less conspicuous to predators.

Among the seabirds that nest in burrows are some species of penguins, shearwaters, petrels, auklets and puffins.

Belted kingfishers, a common species frequently seen along area waterways, excavate their own burrows. Other burrow-nesting relatives of kingfishers include todies and motmots in Latin America and bee-eaters and rollers in Europe.

Even some species of owls nest in burrows. North America's burrowing owl uses abandoned prairie dog dens. The isolated population of burrowing owls found in central Florida excavates its own tunnels in sandy soil, sometimes right in the midst of suburban communities. I've gotten more than a few dirty looks from suspicious residents as I've cruised Florida neighborhoods in search of burrowing owls.

Barn owls and great horned owls occasionally use burrows, too. Barn owls that can't find a suitable tree cavity are capable of digging their own burrows. And in 1982, I spotted a great horned owl watching me from its nest inside an old, enlarged kingfisher hole high on a bank overlooking the Salt Fork of the Arkansas River in Oklahoma.

The largest group of birds, the song birds, has few burrow-nesters. Yet most U.S. birders are familiar with two of them -- rough-winged and bank swallows.

Both species are brown above, light below and about five inches long. The bank swallow is distinguished by a dark band that crosses the lightly colored breast.

Behavior separates these two species even more. Bank swallows nest in large groups. Sandy stream banks and walls of gravel pits may house hundreds of holes. In 1998, I spotted some bank swallows in flight along Route 1 in Maine and discovered a large colony in a mountain of sand maintained by the state highway department.

Bank swallows dig their own burrows with their bill and feet. Progress is slow, perhaps five inches on a good day. Holes are about two inches in diameter and several feet deep. In a dense colony, holes are less than a foot apart, making the embankment look like a huge block of Swiss cheese.

Rough-wings, on the other hand, usually nest singly and usually use an old kingfisher burrow. Occasionally they dig their own tunnels and several times I've seen rough-wings carry food into drain pipes and holes in bridges.

Both bank and rough-winged swallows are found throughout most of the U.S., but their local distribution is tied to the availability of suitable nesting habitat. They are most common where glacial deposits of sand and gravel form stream and river banks.

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