The first biological “footprints” of climate change have begun to appear. Lilacs are blooming earlier. Snow is melting sooner. Bird-watchers say that migratory birds, the heralds of spring in New England, could be among the first to be affected by an altered climate.

A 1999 study of 14 songbirds in Great Plains states supports the theory. After analyzing statistics from the National Audubon Society’s Christmas Bird Count, researchers found that birds begin to change their behavior after just a few winters that are unusually warm or cold.

Throughout Europe and North America, biologists have published studies demonstrating that species of songbirds that travel only short distances are adjusting the timing of their migration to account for an earlier spring.

But birds and butterflies that spend the winter in tropical climes and migrate greater distances don’t see the seasonal changes and continue to migrate on their old schedule – averaging about 13 days late. That puts them on a different schedule than the blooms and insects their chicks depend upon for survival.

“It’s as though they served dinner at 5 and nobody told you, so you showed up at 6,” said Jeff Wells, an ornithologist who lives in Hallowell.

Long-distance migrants may eventually adjust to the changing climate, but scientists have not found evidence for that yet.

Using data from upstate New York, collected since the early 1900s, biologists have demonstrated that tree swallows, which migrate short distances, are laying their eggs 10 to 12 days earlier than they did 50 years ago.

There is not yet any similar evidence of early nesting here in Maine.

W. Herbert Wilson, a biology professor at Colby College in Waterville, worked with several of his students to compare data about bird migrations from the periods of 1899-1911 and 1994-97 and found that nine of the 80 species they studied showed significantly earlier spring migrations. The study did not distinguish between long- and short-distance migratory birds.

Wilson concluded that because so few species had changed their pattern, it’s too soon to cite any signal of climate change here in Maine.

Yet bird-watchers throughout the state insist they’re watching climate change happen through their binoculars.

Carolina wrens, for instance, have become a common sight in southern Maine in the past 15 years.

“I remember driving to Falmouth to see the only nest in Maine,” Wells said. “There are literally just hundreds of them now.”

Tom Hodgman, a biologist with the Maine Department of Inland Fisheries and Wildlife, points to the Northern cardinal – a bird that used to be rare in northern Maine but has slowly built up a substantial breeding population statewide over the past few decades.

Red-bellied woodpeckers have appeared in Maine by the hundreds in the past year or two, said Wells, who believes the sightings could be evidence that the species is pushing its range north in response to climate pressure.

Birds can be difficult indicators, as their migrations are affected by so many other factors. Some scientists argue that the woodpecker “invasion” is related to habitat destruction or that the gradual cardinal and wren boom is in response to backyard bird feeders.

However, the shifts that birders have noticed correspond to many of the forecasts made by scientists, including a wildlife ecologist from the University of Maine, who used data from several climate models to predict how birds’ ranges might change.

If climate change progresses as expected, birds such as the yellow-bellied flycatcher, Philadelphia vireo, evening grosbeak and Tennessee warbler could disappear from Maine altogether, instead breeding in cooler Canada.

Maine’s state bird, the black-capped chickadee, will vanish from southern regions of the state, the study predicts.

“The state bird could be something that [most Mainers] would have to take a trip to see,” Wells said.