Birder's Journal: It's Survey Season for Breeding Birds

By Robert Winkler
for National Geographic News

June 12, 2002

During June, as the nesting season of birds shifts into high gear across
much of the United States and Canada, a small army of birders hits the
road to conduct the North American Breeding Bird Survey.

Beginning half an hour before sunrise, to catch the day's
most intense period of bird song, they drive assigned 24.5-mile
(40-kilometer) routes along secondary roads. At half-mile intervals,
they stop and count the birds they see or hear within a radius of a
quarter mile.

Each of some 3,000 survey routes covered each year requires 50 stops and takes about five hours to complete.

The U.S. Geological Survey's Patuxent Wildlife Research Center oversees the Breeding Bird Survey from its headquarters in Laurel, Maryland.

The methodology has its limitations—roadside observations do not adequately measure population trends in endangered, nocturnal, and colonial-nesting birds. Moreover, sections of road that pass natural areas—including the strips of vegetation often left as buffers between the road and cleared land—can give false impressions.

Species may be common along these sections but absent in nearby areas where habitat has been destroyed.

Despite the "roadside bias" issue, which Patuxent officials are addressing, the more than 30 years of BBS data collectively provide valuable insight into state, regional, and continental population trends of about 500 species of North American birds.

BBS results have helped focus public attention on worrisome changes in bird populations, such as the decline of the cerulean warbler, the eastern towhee, the red-headed woodpecker, and the grassland birds east of the Mississippi River.

Bluebirds Are Back

The news isn't all bad. The number of Eastern bluebirds, for example, increased more than 3 percent a year between 1980 and 2001, according to the BBS. The decline of this species, which nests in old woodpecker holes and in tree cavities formed by natural decay, was noted long before the first multi-state BBS in 1966.

Eastern bluebirds thrive in sparsely wooded habitats: forest clearings, beaver ponds, meadows, and farmland. To feed, they fly from perches and catch insects on or near the ground. Their nesting cavities are often in dead, isolated trees.

Early in the 20th century, the open habitats the bluebird requires were reverting to forest. Meanwhile, commercial and residential developers, and managers of timberlands, were removing the bluebird's existing nest sites. Dead trees were regarded as unsightly, and their wildlife value wasn't appreciated.

Competition from the house sparrow and the starling—aggressive cavity nesters introduced from Europe in the 1800s—and pesticide poisoning in the 1950s and 1960s worsened the bluebird's plight.

In the 1930s, the bluebird's early advocates were promoting "bluebird trails"—a series of nest boxes woven through appropriate habitat—but it wasn't until the 1970s that bluebird restoration on a massive scale took hold.

Today, The North American Bluebird Society—dedicated to helping Eastern, Western, and mountain bluebirds, as well as other native cavity nesters—has more than 4,000 members, and its Transcontinental Bluebird Trail comprises more than 20,000 nest boxes.

There are also a number of state and provincial bluebird societies, and on the Internet, there's The Birdhouse Network, a nest box monitoring project of the Cornell Laboratory of Ornithology.

The Birdhouse Network maintains data on more than 30 species of cavity nesters, displays pictures from nest-box cameras, and sponsors "citizen science" research. Like BBS volunteers, bluebird society members and Birdhouse Network participants are especially busy in June, monitoring nest boxes at the height of the breeding season.

Nest Boxes for Bluebirds—and Swallows

More than 100,000 nest boxes are sold annually, and do-it-yourselfers build countless others. Eastern bluebirds have also benefited in recent decades from the comeback of the beaver, which builds dams that flood riparian woodlands. Beaver ponds often contain dead, hole-ridden trees.

Installing a bluebird nest box is not a project to take lightly. It's not enought to nail a nest box to a tree and forget about it—that would be tantamount to serving predators a bluebird platter.

If a nest box doesn't meet specifications, if it's not a safe haven, if the wrong site is chosen, or the box is not monitored for problems, birds—if any move in—are far less likely to survive and to nest successfully. (The Bluebird Monitor's Guide by Cynthia Berger et al. and The Backyard Birdhouse Book by René and Christyna M. Laubach are helpful guides to all this.)

Aside from commitment, an avian housing program may require a significant outlay of cash, especially for anyone who's mechanically challenged. For my store-bought bluebird nest box, metal mounting pole, stovepipe-style raccoon guard, and attachment hardware, I paid over $90—more than three times what Henry Thoreau paid to construct his cabin on Walden Pond. My building materials, furthermore, were harder to find.

Put yourself in a cavity nester's place, and you'll see justification for all the fuss.

When you're seven inches (18 centimeters) long and weigh little more than one ounce (28 grams), the placid suburb is fraught with dangers: domestic cats, raccoons, hawks, nest-robbing birds such as jays and crows, squirrels, snakes, wasps, blood-sucking flies, competing cavity nesters, and human vandals. Hunkered in a wooden hole, your one escape route is likely to be blocked by the predator that has come to eat you.

Contaminated waterways, noise pollution, and pesticides pose additional threats.

Of course, predation, accidents, and disease are natural in the wild, and if you spend time helping wildlife, you're bound to experience tragic losses, as I did in early May.

My nest box attracted a tree swallow—a species that often uses boxes designed for bluebirds. The swallow spent most of two days resting inside the box. Once, when I opened the hinged front panel, it flew out, skimmed the surface of a nearby pond for a drink, and circled higher to catch flying insects.

I thought it was okay, perhaps waiting for the arrival of a mate, but when I checked the box on the third day, the swallow lay dead inside, with no visible injuries.

The mysterious circumstances of the death disturbed me but gave me no reason to abandon my project. After cleaning the box, I put it back up, and though bluebirds inspected it, a pair of tree swallows moved in. Tree swallows seem less common in my neighborhood than bluebirds, so I'm thrilled.

Right now, the female swallow is in the box, brooding the clutch of eggs in her feather-lined nest. The male stands guard on a snag curving over the pond. Sometimes they zoom around together, showing their incredible flying skill as they pick off insects.

If my curiosity brings me too close to the nest box when the protective female is outside, she dives at me while calling aggressively. I respect her wishes: I turn from her nest box and head toward my own.

Robert Winkler, a nature writer, is working on a book about his adventures with birds in the "suburban wilderness" of southern New England. Visit him at his Web site.

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