National Geographic : 1993 Jun
the needs of each. Dan Niven, an energetic doctoral student at the Uni versity of Illinois, has been studying the hooded warbler, which nests in dark, dank lowland woods where its golden feathers sparkle like a firefly on a black June night. "For a tract of forest to be right for hooded war blers," Niven explains, "it must have tree-fall openings, like those caused by a windstorm, which encourage dense vegetation. That's where the parent birds will tend their fledglings." Yet when aging or dis eased trees topple and create sunlit gaps in the forest canopy, the least flycatcher, a diminutive scourge of insects and spiders, will abandon a favored breeding site. To further complicate matters, sev eral Neotropical migrants are segre gated by sex on their wintering grounds. Niven has followed the hooded warbler to Yucatan, where males occupy mature forests while their mates prefer open scrubland. "We can't expect to save all these places in pristine condition," he says. "We need to find out what impact different levels of disturbance, like logging, will have on the birds' sur vival rates over winter." Many factors also influence whether birds raise their young suc cessfully. As Vickie McDonald has discovered in her studies of Kentucky warblers at the National Zoo's Con servation and Research Center in Vir ginia, overbrowsing by white-tailed deer destroys critical cover for birds that nest on the ground or in the for est understory, leaving them vulner able to predators or even homeless. Survival of nestlings can be jeopar dized by insect shortages or by an increase of nest-plundering blue jays. And always lurking is the brown headed cowbird, a vagabond of the blackbird tribe that furtively leaves its eggs in another bird's nest, where its young are raised by unwitting sur rogate parents. Because the situation is so com plex, there is no quick fix such as reg ulations banning the use of persistent pesticides, which eased the earlier crisis. As I was told time and again, staying or reversing the decline of the songbirds calls for profound changes in how we manage our public and private landscapes-plus a major effort to restore lost habitat. Although no one predicts mass extinctions in the foreseeable future, ornithologists say that many Neo tropical migrants like the cerulean warbler and wood thrush will con tinue to fade from places where they had been common. Some believe a few species could become exceedingly rare. John Terborgh, director of Duke University's Center for Tropi cal Conservation, warns that the last unprotected rain forest in Central and South America could disappear within 40 years, with grave consequences for birds tied to mature habitat. Ter borgh claims, "We are as helpless as bystanders at a car crash." AM DROEGE cocks his head from side to side like a great horned owl listening for scurrying mice. "Three wood thrushes, at least," he says, jotting numbers on his clipboard. A pewee whistles its name. A field sparrow trills. The watch beeps. Time to move on. There are strict rules for Breeding Bird Survey participants. Starting time, for example, is exactly 30 minutes before sunrise. Stops are exactly one-half mile apart, and the observer counts every bird heard or seen from a stationary point in exactly three minutes. Drive, stop, count birds. Drive, stop, count birds. Four hours of driving, stopping, counting birds. Boring? Not to serious birders, who crave the challenge of identifying hundreds of species from snippets of song or a flash of color. Droege navigates by detailed topo graphic maps with landmarks noted in orange. At stop 18, for instance, nature is reclaiming an old drive-in movie theater, and trumpet vines twining about rusting lampposts have lured our (Continuedon page 82) Silence of the Songbirds Birds of a feather rest in peace together at the Smithsonian Institu tion's 600,000-specimen collection in Washing ton, D. C. "Research here saves hours in the field," says ecologist Mercedes Foster,noting that biologicaldata accompany many speci mens. Another collection includes a palette of paintedbuntings (left), birds now vanishinginto Mexico's pet trade.