If there is a migrating monarch butterfly flitting across the mouth of the Chester River, Pat Durkin will spot it.
Durkin, who is doing the first on-the-water census of these elegant creatures, counted 814 as they streamed past her in one hour on a late September day, headed unerringly south by southwest. A week ago, she saw 67 in an hour.
But yesterday, with the temperatures barely in the mid-50s and the wind whipping out of the north at about 15 knots, only small birds skimmed the surface.
It strengthens her belief that "monarchs do what makes sense" for them on their annual 3,000-mile journey to the Oyamel forests in the mountains of central Mexico, says Durkin, who has been sailing a four-mile stretch of the river twice a day for the past three weeks, the time migrating monarchs fly through Maryland.
"They don't fly when they have the wind in their teeth, and they don't fly in the rain. And because they have such a long way to go, they try to get off as soon as it gets warm enough in the morning," she says. Yesterday, it wasn't warm enough.
Durkin is among a group of volunteers counting monarchs for Lincoln Brower, an internationally known expert on monarch butterflies and a research biologist at Sweet Briar College in Sweet Briar, Va. The other volunteers -- in Cape May, N.J., and Chincoteague, Va., are doing it from land.
Durkin's project, called Butterflies Over the Bay, ends today. It will provide basic information about the monarch migration over water, Brower says.
"All we have is anecdotal information," Brower says. "Somebody saw some on their sailboat, somebody saw some somewhere else. Pat's getting the alpha basic information we need on migration."
Brower says he fears the loss of monarch habitat in Mexico might destroy their migration -- the longest of all butterflies -- and the species as well. The more scientific information he and others can gather, the more ammunition they will have to argue for habitat protection.
That's where volunteers like Durkin come in. As she counts butterflies from the deck of Esmerelda, her 34-foot sailboat, she also notes wind speed, temperature and other conditions that might affect the insect's flight.
"We don't know if they actually cross water," she says, "or how wind over water affects them. But what we learn could help make a case for preservation."
Monarchs are threatened by logging that is destroying their winter homes in Mexico and by pesticides in the United States that kill milkweed, the monarch larvae's exclusive food source.
The pollen from an increasingly popular commercial corn has killed monarch caterpillars in laboratory tests. Scientists fear its effects because pollen floats through the air, coating nearby milkweed.
In response, the Mexican government has set aside five of the 12 monarch wintering spots as sanctuaries, but logging continues on the others and sometimes in the sanctuaries. Brower is working with the World Wildlife Federation and the Mexican government on a plan to protect the butterflies.
Some scientists call monarchs an indicator species, one whose troubles point to other problems in the environment. But Durkin, a founding member of the Washington Butterfly Club, prefers to call them "poster butterflies" for conservation.
"How many people are going to get excited about a little, 3-inch-wide butterfly with a habitat 50 yards wide," she asks. "But everyone knows about monarchs. It's a species that can call attention to conservation issues."
In late August, the monarchs begin pouring down the East Coast from as far north as the Arctic Circle, headed for the forests, and often the same trees their great-, great-, great-grandparents left the previous March.
The migration has passed its peak in the mid-Atlantic states, and the first strong surge has reached Texas, according to reports this week on monarch butterfly Web sites.
The butterflies arrive in Mexico on Nov. 1 or 2, coinciding with the Day of the Dead festival and they are described in local folklore as spirits of deceased relatives returning home.
In mid-March, the butterflies begin the journey north, just as milkweed plants are beginning to bloom in the Gulf Coast states. Females lay their eggs on those plants and die.
Succeeding generations continue the journey until the monarchs that spread their wings all across North America in late August, bigger and stronger than their immediate precursors to survive the rigors of travel, begin the return trip south.
It is this "elegant migration" of these "beautiful, sensual creatures" that is so important, says Durkin.
If the migration is destroyed, adds Brower, "we are destroying something culturally as valuable as the Mona Lisa or the stained glass windows in the cathedral at Chartres."