READFIELD – Loon counters were out in force this weekend in Maine, as more than 700 volunteers took to the state’s lakes and ponds listening for loon calls and looking for signs of one of the oldest bird species in North America.

The 19th annual loon count was sponsored by the Maine Audubon Society to help biologists gauge the bird’s overall health. Loons face increasing pressure from shoreline development and threats from lead, mercury and dioxin poisoning.

Audubon’s loon tallies will be available in September, but Maine’s estimated population is 4,300, making it the loon capital of New England. Loon counts also were held in Vermont, New Hampshire and New York on Saturday.

Among Maine’s loon counters was Bonnie Urquhart, who was on Maranacook Lake from 7 to 7:30 a.m. with her husband and daughter in search of the red-eyed birds. Five minutes after the family’s motorboat left the dock, they spotted an adult and chick on the lake’s east shore.

“The chick is about 10 days old. The parents are both very good. They both incubate the egg,” Urquhart said.

A short distance away, the other parent floated on the water. Immediately after seeing the birds under ideal conditions, Urquhart jotted down times of the sightings and approximate locations.

In Vermont, more than 200 volunteers – binoculars at the ready – headed to the state’s lakes and ponds Saturday morning for that state’s loon watch. Vermont’s event is sponsored by the state Department of Fish and Wildlife and Institute of Natural Science.When the Vermont survey began in 1983, only 100 lakes were checked, while this year about 160 lakes were posted with loon watchers.

“We’ve expanded it out a little bit because the [numbers of] loons are expanding,” said Eric Hanson, a biologist with the Vermont Loon Recovery Project.

Loons were so rare in Vermont in the mid-1980s that the state put the bird on its threatened list in 1987. Now, with the population returning, the state will likely start the process of removing the loon from that list, Hanson said.

Dan Lambert, a conservation biologist with the Vermont Institute of Natural Science, said loons are widely loved because they are “charismatic” and possess a “striking appearance.”

“The birds let out a wide variety of yodel-like, high-pitched calls and are easily distinguished by their characteristic ‘white necklace,’ black and white speckled feathers, sleek black head and red eye,” he said.

The growth in the loon population has been attributed to several factors.

The use of artificial nesting platforms more resistant to flooding, floating signs that warn boaters about the location of nests, and voluntary help from hydroelectric companies that have stabilized their water levels during key nesting periods have all played a part in increasing the loon population.

Lambert said that as their population grows, loons’ geographic range does as well.

“The heart of loon country in Vermont is in north-central and northeastern Vermont,” he said. “But we are finding that … the geographic range of breeding loons is increasing in the state, including down into southern Vermont.”

The biggest threat to the loons in Vermont – and in other areas – continues to be the use of lead fishing sinkers and other discarded fishing tackle, according to Steven Parren, the chief of the Non-Game and Natural Heritage Program for the Vermont Department of Fish and Wildlife in Waterbury.

“We’re trying to do public awareness building and there have been some sinker exchange programs, but we are still loosing loons to lead,” Parren said.

Nonmotorized watercraft are recommended for watching the birds because there is less chance of running over loon chicks, Lambert said. Bird-watchers in all watercraft should remember to give nesting loon families a wide berth and avoid close approaches. Binoculars also are recommended.