BENTON — A decade ago, biologists didn’t know how many nesting pairs of great blue herons there were in Maine – or where the birds migrate to in winter.

Since then the state’s great blue heron study has shed some light on this reclusive bird.

Through the study, biologists with the Maine Department of Inland Fisheries and Wildlife hope to learn more about where the herons are most abundant. State bird biologist Danielle D’Auria, who leads the project, also seeks to know about the timing of the herons’ return to Maine each spring.

The great blue is the largest heron in North America, standing more than 4 feet tall with a 6-foot wingspan and distinctive yellow bill. It has a lifespan of about 15 years.

They nest in the same colony, or rookery, each year. Generally these colonies have dozens of nests bunched together in areas with sparse human populations. The birds nest together for protection from predators like eagles, foxes, hawks and raccoons.

Great blue herons are common in Maine, but a decline in the coastal nesting population since 1980 caused concern among state biologists. So IFW recruited volunteers to help check colonies, which are often far from trails or roads.

During the first eight years of the study biologists used as many as 80 volunteers to confirm where existing colonies were and roughly how many nesting pairs there were in each colony, D’Auria said.

Two years ago, radio transmitters were put on five herons in Maine. The transmitters affixed to the birds send out a GPS signal showing the birds’ flight pattern while it forages in its summer colony in Maine and where it migrates in the winter.

A heron in Palmyra that was affixed with a transmitter in 2016 flew to Haiti two years in a row and foraged there throughout the winter in an area only a few square miles in size. Another heron went to the Bahamas to winter, and a third went as far as Cuba before its transmitter was lost, while a fourth died on migration. The fifth heron in the study only went as far as Vero Beach, Florida, but there the bird turned a backyard dock into its regular hangout.

This spring, two radio transmitters that were lost were replaced when two herons were trapped near Newport and in Orrington. But already, state biologists have learned more about the herons that nest here.

Last year, state employees and volunteers surveyed 60 active colonies with 629 nesting pairs. But D’Auria said the state estimates there are as many as 1,500 nesting pairs statewide.

She also hopes to gather data on why colonies fail, so that if the statewide population declines biologists will have some idea why.

“Some colonies persist for 40 to 50 years,” said D’Auria as she checked on a long-standing colony in Benton in June. “In Maine, we’ve had some sites since the ’70s.”

The radio transmitters have brought new information – and more questions – to the study, she said.

A month ago she trapped and tagged a heron in Newport with the volunteers who helped tag another heron there two years ago. Now volunteers from nearby Nokomis High are eager to see if the heron trapped there in June goes to the same wintering grounds in Haiti as the last bird from the Newport colony.

“Right now we’re waiting to see where she goes,” said Nokomis teacher Bill Freudenberger. “We do know she’s a mature bird. But we don’t know yet where she goes.”

Freudenberger said it’s exciting that the work he and his students have done for the heron project – maintaining bait sites to lure the herons – has helped biologists learn more about the mysterious birds.

The students frequently watch the tagged herons online – at movebank.org – to see where they feed in Maine and then where they spend the winter.

“Students get excited if they see the bird feeding near their house,” Freudenberger said. “We have a message board at school with a TV with a slide show. It shows where the heron is in the world. The kids keep track of her and tell me if they saw her. When they see a heron outside the school, they wonder if it’s our bird.”

In June, Freudenberger and a few of his students baited a site at a pond with small fish to lure heron. They checked the bait site each day for weeks. When they were certain a heron was feeding there regularly, they told D’Auria. Then together they trapped the bird.

Sophomore Beau Briggs jumped at the chance to help trap the bird even though that meant getting up at 2 a.m. to go to the bait site and sit for three hours until the heron came to feed. Briggs said the feeling he experienced when he watched the bird being netted by D’Auria and handled by the biologist was incredible.

“It was an adrenaline rush,” Briggs said. “The biologist did the actual capture with the net, but we all ran out when it was trapped. It was exciting because we took so much work into baiting it – but it worked. I will never forget it.

“I was in ninth grade when I first heard about the heron project. I thought it was cool how they tracked their migration pattern just from this tiny transmitter that’s like a backpack .”

The Newport colony is unusual in that it is in a stand of mature eastern white pines far from the coast. The herons here frequently fly over the soccer field at school. But Freudenberger said the students steer clear of the colony to avoid disturbing it.

Most of the colonies seem to be along the coast or the islands. But in the next year, D’Auria hopes to trap and tag a heron from landlocked Aroostook County.

“There are accounts of nests there. But it’s an area we don’t have a lot of reports from,” D’Auria said. “It would be exciting to get a bird from a different part of the state.”