Tiny, light-sensitive devices strapped to the backs of purple martins and wood thrushes in their northwestern Pennsylvania breeding grounds have yielded the first clear picture of songbird migration routes and over-wintering areas, information that could eventually help pull songbird populations out of a long tailspin.

The migration study, to be reported in the journal Science tomorrow and funded in part by the National Geographic Society, marks the first successful tracking of songbird migration routes and also shows that scientists have significantly underestimated their flying ability.

The data collected shows the birds flew more than 311 miles in one day, compared to previous studies that estimated their flight performance at 93 miles a day. The study also revealed that prolonged stopovers were common on the fall migration to the south and their migration was two to six times more rapid in the spring than in the fall.

The two purple martins tracked in the study from their breeding grounds around Edinboro Lake in Erie County stopped in the Yucatan Peninsula of Mexico for three or four weeks before continuing on to their wintering-over grounds in Brazil. One of those birds took 43 days to fly down to the Sao Paulo area of Brazil but only 13 days to return.

"We were flabbergasted by the birds' spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding," said study author Bridget Stutchbury, a professor of biology at York University in Toronto, Ontario. "No one had any idea these little songbirds would be able to fly that far that fast. That was the gee-whiz part."

The study also uncovered evidence that wood thrushes from a single breeding population located in Hemlock Woods, near Cambridge Springs, Crawford County, did not scatter over their tropical wintering grounds but stayed in a narrow band of tropical forest in eastern Honduras and Nicaragua.

That region is clearly important to the overall conservation of wood thrushes, a species that, like the overall songbird population, has declined by 30 percent since the mid-1960s, Ms. Stutchbury said.

The tracking data research is important, she said, not only to protect at-risk species of songbirds but also to assess environmental and habitat loss related to deforestation, pesticide use and climate change.

"There are many songbird species showing significant, chronic, long-term declines, and in order to stop that we need to understand if the wintering grounds are causing or contributing to that," Ms. Stutchbury said.

"Until now our hands have been tied in many ways because we didn't know where the birds were going when they left in the fall. They would just disappear and come back in the spring. It's wonderful to now have a window into their journey."