They arrive beginning in April, coming into the United States and Canada under the cover of night, moving in large groups.
They are warblers, sometimes called the butterflies of the bird world because of their bright range of colors and diminutive size.
They fly in mixed-species flocks, eat mostly insects, make all kinds of noise, and many are no bigger than a man's thumb.
Warblers are not the most common songbirds in the United States, experts say. That distinction may well fall to the sparrow. But they are amazing aviators.
Many migrate from the rain forests of Brazil to the Canadian Rockies, the Upper Peninsula of Michigan and Upstate New York, where they breed in the marshes, grasslands and the thickest forests they can find.
In fall, the blackpoll warbler flies from New England to South America. It increases its body weight 20 percent for the four-day trip, a 2,500-mile nonstop flight riding sea breezes over the Caribbean.
This spring and summer, the National Audubon Society and the Cornell Laboratory of Ornithology are asking bird-watchers across North America to participate in "Warbler Watch."
They want bird-watchers to post on the Web the numbers and arrival dates of the more than 50 species of warblers that migrate to the United States and Canada to breed this month.
John Fitzpatrick, director of the Cornell Lab of Ornithology in Ithaca, N.Y., says the count is important to help scientists understand whether the number of warblers is increasing or on the decline.
Like most birds, warblers serve as indicators of what the environment holds in store for mankind, he says. Effects of DDT on the peregrine falcon served as a warning of the pesticide's effects on humans.
"If we don't care to take a look at the birds around us and the signs they give us, then we're failing to see signs of change before our eyes," Fitzpatrick says.
"It's like the canary in the coal mine. If the canary died, the miners knew it was a sign of danger.
"It's the same with other species of birds that give off warning signs. Birds are extremely sensitive indicators of our environment and its changes."
Warbler Watch began April 6, about the time the warblers began arriving in the Gulf Coast states. It will continue until July, when all the warblers have arrived.
Bird-watchers can report warbler sightings by logging on to the Web site and following the instructions provided. The site offers tips on on how to spot warblers, what to watch and listen for, maps of their ranges and updates on conservation efforts.
The Web site address is: http: //birdsource.cornell.edu.
There is no way, Fitzpatrick says, to make sure every sighting reported is accurate. Reports are checked against what is known about the species being counted. Those filing reports are required to include an e-mail address.
"We examine the information to see if it's basically believable, and then once we sift out the information that's not, we look closely at what's left," Fitzpatrick says.
Researchers also look for overall patterns that are reported by hundreds of bird watchers.
"The more information you get," he says, "the harder it is for any pattern to emerge unless it's true. You won't get hundreds of people making the same error."
Three thousand warbler sightings have been reported on the Web site so far -- fewer than were expected, according to Allison Wells, a spokeswoman for the Cornell lab.
It could be that the warblers are moving swiftly to their nesting grounds this year because the winds have been relatively calm and the nights clear, she says.
"There are a lot of theories, but the fact is we really don't know," says Wells.
Fitzpatrick says warblers were selected for the count because they occupy such a wide range of North America and are popular among bird fans.
The U.S. Fish and Wildlife Service says its 1996 survey found 44 million backyard bird-watchers in the United States.
Roughly 18 million bird-watchers also traveled from their homes to watch birds at parks, woods, lakes and other sites in 1996, according to the survey.
Chan Robbins, a wildlife research biologist with the Patuxent Wildlife Research Center in Laurel, says about 30 species of warblers can be spotted in Maryland and their numbers have remained steady over the years.
The most common warblers sighted in Maryland are the Kentucky warbler, yellow warbler, black and white warbler, common yellow throat, pine warbler, American redstart and the ovenbird, which makes an oven-shaped nest on the ground in the forests of the eastern United States.
Fitzpatrick says Warbler Watch will be conducted each year and provide a first-of-its-kind database to track the birds' migration routes and numbers.
It may be of particular assistance, he says, in determining the fate of such rare songbirds as the cerulean warbler and golden-cheeked warbler.
The sky-blue cerulean, which winters in the foothills of the Andes mountains, breeds each spring in stands of old-growth forests in Canada and the eastern United States. Its numbers have declined about 4 percent each year since 1966 in the United States.
Some ornithologists think the cerulean may have shifted its summer breeding grounds north to parts of Canada.
"This could be a species that shows an example of a continental shift in its habitat, and their numbers may be expanding in Canada," Fitzpatrick says. "We just don't know."
fTC The golden-cheeked warbler, which breeds only in the forests of central Texas, is listed as an endangered species by federal officials.
If it disappears, it will not be the first. Since the early 1900s, loss of habitat has led to the disappearance of the Carolina parakeet, the ivory-billed woodpecker and the passenger pigeon, which used to migrate from Georgia to Wisconsin.
Bachman's warbler, a bird once indigenous to the marshy areas around tobacco and cotton fields of the southeastern United States, hasn't been seen since the 1950s and is believed to be extinct.
The news isn't all bleak.
"There are a fair number of species that are stabilizing, and numbers are actually increasing for some species," Fitzpatrick says.
The hooded warbler, in olive and yellow considered one of the most spectacularly colored birds in the eastern United States, is making a comeback and its numbers have stabilized.
But it is threatened by deer that have proliferated along the East Coast, says Robbins. Deer eat the dense undergrowth of shrubs in the woods where the bird makes its nest.
Fitzpatrick has high hopes for Warbler Watch. A bird-watcher since his childhood in White Bear Lake, Minn., he has become an articulate spokesman for birds and what they mean to mankind.
They are a harbinger of spring, bringing music, color and variety into our lives, he says, and they contribute to the balance of nature and to our aesthetic sense about what is important in life.
"Humans have a very close relationship with birds and have had a close relationship for thousands of years," Fitzpatrick says.
"Birds renew our sense of the importance of nature and of nature's cycles, and it is important that the relationship continue."
Pub Date: 6/21/98