The day was cool and overcast, with strong, gusty winds. The rain predicted for the day seemed imminent. Yet not one member of our group regretted coming out to Acadia National Park on Isle au Haut; we were there to spot harlequin ducks and assist biologist Glen Mittelhauser in reading leg bands of tagged birds.

We were headed toward Merchant’s Cove, “the best place to see harlequin ducks on the island,” Mittelhauser said. He wasn’t kidding; about 80 birds were there, some floating and diving, others “hauled out” on rocky, seaweed-carpeted ledges.

The birds had traveled there from their breeding grounds in eastern Canada. In the summer, they nest near and forage in raging rivers; come October, they migrate to the coasts of Canada and the United States. Some of them come to Maine, where they spend their time diving for marine invertebrates, or hauled out on rocks to rest and preen.

It is then that we have our chance to read their tags. The birds were fitted with colored bands on their legs, just above their feet. A two-digit code was printed vertically on each, and the characters had to be read from the foot up. Yellow bands indicated they were banded in Canada; white bands indicated they were banded here, off the eastern coast of the United States.

One bird’s leg band read “N9,” and was colored yellow.

“We saw this bird on Celeste Island in Labrador,” Mittelhauser said, adding that the island’s name was unofficial and is not on any map. He had named it after his daughter.

Soon more bands were deciphered: “C4-yellow,” was banded on the Gannett Islands, in Labrador, in August 1999; “C4-white” was seen five times on those islands in the summer.

Through these banding studies, Mittelhauser is able to connect a bird’s breeding area with its coastal, or wintering area; can determine if the birds remain faithful to particular sites; and is able to monitor individual survival rates and estimate population sizes. Currently, their numbers seem to be slowly increasing in eastern North America, but that wasn’t always the case.

In a paper published in the journal Northeastern Naturalist, Mittelhauser and his peers reported that the birds had experienced large population declines off the coast of Maine at least twice in the past. The first occurred in the mid- to late-1800s, when a researcher warned the harlequin would be gone from Maine by the early 1900s. The birds hung on, though, but dropped in numbers again in the 1980s, due in large part to hunting pressure. Finally, the bird was listed as a state threatened species in 1990 and protected from hunting.

Today Mittelhauser estimates that between 1,150 and 1,300 birds – more than half of the wintering population in eastern North America – winter in Maine. Almost 75 percent of these birds can be found around Isle au Haut, Vinalhaven Island, and Swans Island. This makes it doubly important that the birds continue to be monitored and protected, a job that Mittelhauser is committed to wholeheartedly.

He has come a long way from when he first began his study of the harlequin duck on Isle au Haut 14 years ago. Then, he had picked up the project just to have something to do for his senior thesis at the College of the Atlantic. But somewhere along the way, something changed. Mittelhauser summed it up simply.

“I fell in love with the Island, and I fell in love with the birds.”

Chris Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com