It’s been a weird winter, with mild and rainy weather confounding people who try to organize traditional winter activities. It turns out that the warmer winters have also led to changes in the behaviors of at least one animal: loons.

Biologists at the Loon Preservation Committee in Moultonborough have observed or rescued many loons that didn’t make the usual seasonal migration to the ocean this year, instead staying behind to ride out the winter on lakes.

Two such birds caught the attention of Carol Varney, who lives on Lake Opechee, on Feb. 21. “I noticed the lake had really iced in, but there were pockets of open water,” Varney said. “There were two loons that were swimming around an open area,” which she estimated to be about 25 feet wide.

Loons have some significant physical characteristics distinguishing themselves from other aquatic birds. They have solid bones, instead of hollow bones as most birds have, and their denser bodies make it harder for them to take flight. Their feet are also positioned further back on their bodies, which is better for swimming underwater, but they are unable to walk. These two traits result in a need for loons to have a broad stretch of open water for them to take flight.

According to Caroline Hughes, biologist for the Loon Preservation Committee, loons that get iced-in are at great risk. If they are forced onto the ice, they have no way to find food for themselves, and become easy pickings for land-based predators. If the area of open water shrinks, they can become targeted by bald eagles, since they have little way of escaping.

Typically, New England’s loons fly to the ocean in late fall, where they will spend their winters. It takes an expert birdwatcher to spot them there, because their plumage transitions to a drab mottled gray in their winter time.

The Loon Preservation Committee is well practiced with rescuing loons from partially iced-in lakes, but Hughes said that normally happens in early winter, when loons — typically those born earlier that year — miss the opportunity to begin their migration and find themselves without enough open water to take off. Increasingly, though, they’ve been responding to reports of loons still on lakes late in the winter, including last month on Lake Opechee.

“We’re thinking that it’s loons that never left,” Hughes said, noting they’ve noticed a trend of more reports of iced-in loons later in the season over the past few winters. Last year, in February, she and her colleagues rescued a large group of loons from Lake Winnipesaukee.

This winter, the Loon Preservation Committee rescued two loons in December, and eight since Jan. 1. They’ve also been monitoring a group of about 15 adult loons that have spent the winter in The Broads on Winnipesaukee.

Sometimes loons have a medical issue that prevents them from beginning their migration in time. Whenever they capture an iced-in bird, they take it to a veterinarian, such as VCA CAVES in Concord, Meadow Pond in Moultonborough or WINGS Wildlife Rehabilitation in Henniker, which all volunteer their services to evaluate the animals. In two cases this year, there was a diagnosis they could point to — one had lead poisoning, while the other had a respiratory infection — but the rest exhibited no reason why they couldn’t have left on time.

Of the 10 loons rescued this year, four were adults, old enough to have made the migration before, yet didn’t this year, for reasons unclear to the biologists who are studying them.

“We speculate that it might have to do with climate change,” Hughes said. “It could be that cues that trigger migration are happening later. It could also be that we are seeing the start of loons starting to winter over on lakes rather than going to the ocean.”

The overwhelming majority of the region’s loons are continuing to migrate as they always have. Attempting to spend the winter on freshwater is risky, because not only will the lake likely freeze over, loons lose their flight feathers during a winter molt, so they might not be able to fly even if they get enough open water.

“We could be seeing these pioneer loons trying to make it work,” Hughes said, emphasizing the explanation is “total speculation” at this point.

Hughes said she considers it “likely” a response to the changing climate, though she added it could also be there are more people aware of loons, leading to increasing rates of reports. She added there are warmer parts of North America, such as the Carolinas, where it is more common for loons to find a freshwater place to winter.

When Hughes and fellow biologist John Cooley responded to Varney’s call last month to Lake Opechee, they found just one loon sequestered in a patch of open water off Opechee Point, where Varney had observed a pair the prior day. Hughes said they could see other loons further out in the lake, where there was more open water, and she guessed one of the two managed to swim under the ice to the larger section of the lake.

Cooley, wearing a cold water suit and pushing a small boat, crossed the ice and approached the loon, which he caught with a net. They brought the bird back to shore and transferred it into a cardboard box. Then, after ensuring it was in good health, they banded it and released it at the Seacoast.

Hughes said the loons they have rescued in previous winters have returned to the Lakes Region in the spring and had successful breeding seasons.

If people see loons in open water in the winter, they might not need rescuing. However, if they are in a patch of water less than 20 feet across, or if they are being stalked by eagles, Hughes suggested giving the Loon Preservation Committee a call at 603-476-5666, or submitting their concern via loon.org/report-loon. She said photos, if possible, are especially helpful when it comes to assessing a report of a loon in distress.

“There have been a number of loons that we’ve been called about but we haven’t rescued,” Hughes said. “With the alternating pattern of cold and warm weather, as soon as we’ve been concerned, the ice goes back out.” And, looking at the long-term forecast, “We’re hoping the loon rescues are done for the season.”