PORTLAND – A scarcity of birds at backyard feeders has left northern New England bird-watchers scrambling for an explanation.

“Our feeders are so lonely,” said John Cole, who has four feeders in the back yard of his Brunswick home. “Normally, I put in a new suet cake every 10 days, but it’s been six weeks. It’s like the desert. … Nothing’s here.”

In Maine, empty feeders have been reported from Castine to Kennebunk. Bird-watchers elsewhere in New England are reporting similar problems.

“I’m seeing no birds,” said Ed Oechsle, a member of the nationwide Project Feeder Watch, who lives in East Kingston, N.H. “I’ve been observing birds for 30 years, and it’s never been this bad.”

Bird-watchers throughout the region have been calling local bird centers to find out what’s gone wrong, but experts can only speculate on the reasons for the empty-feeder phenomenon.

By this time of year, chickadees, tufted titmice, nuthatches, goldfinches and blue jays have usually left the shelter of the forest to crowd backyard bird feeders. But to date, only a few have been seen.

Some suggest that abundant wild food and mild weather are keeping the birds in the woods longer than usual.

“Wild birds prefer feeding in the wild,” said Judy Walker, a staff naturalist with the Maine Audubon Society. “Nobody is reporting sick or dead birds. All the population data we have is normal.”

Judy Kellogg-Markowsky, director of the Fields Pond Nature Center in Holden, said she’s had a lot of calls about the apparent scarcity of birds at feeders.

“It’s a slow season for birds because it’s been a warm fall,” she said. “There is still lots of wild food available, such as insect eggs, fruits and seeds.”

However, her feeders had a big influx of hungry birds over the past weekend, when the temperatures dropped. “They needed a concentration of calories,” she said.

Also, chickadees appear to be more migratory than some people may think. The birds they band at the center do not always show up at the feeders the next day. Instead, unbanded birds will arrive for a meal.

“They all look alike, so we may think they are the same birds. They might go to New Jersey or come from Canada,” she said.

Tom Hodgman, a biologist with the Maine Department of Inland Fisheries and Wildlife, says he’s seen plenty of wild birds in the woods north of Bangor. He found an abundance of berries, seeds, nuts and cones, a result of the wet, cool summer.

Cole, among others, remains skeptical, saying the woods near his house are virtually birdless.

“We’re right on top of woods,” he said. “I see what’s going on. I walk in the woods. There are no birds in the woods.”

Jonathan Harris, who owns Feed the Birds in Wiscasset, says sales at his store are down 60 percent. He believes birds have simply left the area, but doesn’t know why.

“There’s plenty of food in the woods every year,” Harris said. “Birds are out there, but not scads of them, as you’ve experienced. There’s something very wrong.”