It seems as if predictions for this winter’s finch invasion are holding true. Pine grosbeaks continue to be reported and, on my way in to work this morning, I saw several along the old College Avenue Extension road in Orono.

A few were actually in the middle of the road, apparently attracted to the salt and sand there.

Redpolls are also beginning to be reported. I’m no scientist, but I wonder if more of these birds are present at this time of year than was originally predicted. Writing for the Cornell Lab of Ornithology’s Web site, Ron Pittway, of the Ontario Field Ornithologists, predicted most redpolls would remain north. He judged their favorite winter birch-seed crop as “average to good in many parts of northern Ontario” but, he said, some may wander south in mid-winter as the seed crop diminishes.

He also added that these and other winter finches are more nomadic than is usually thought, so they very well could end up at many people’s backyard feeders.

And they have. I got a kick out of reading people’s posts on the Maine-Birding list-serve.

“The redpolls are coming, the redpolls are coming!” exclaimed one birder. Several posts after that all had the same thing in the subject heading: redpolls. redpolls. redpolls.

One birder wrote of seeing five redpolls at his feeders one morning, then looking again sometime later and seeing 50 mobbing the stations.

Another wrote of a flock actually mobbing him as he filled the feeders. The birds were landing on him and taking seed right out of his hands.

As are other northern species that live in sparsely populated areas of the North, redpolls are quite unafraid around humans. Their cyclic invasions bring them only into sporadic contact with us; some years most will not leave their far northern breeding ranges at all.

As a result, their unwary and confiding nature beguiles us birders, making them favorite winter visitors.

There are two types of redpolls: Common and hoary. Both are similar in appearance and sometimes it takes a trained (strained?) eye to tell them apart, especially when there are one or two hoary redpolls in amongst a flock of commons – as is often the case.

But their moniker suggests the difference, most noticeable in males with fresh plumage: Their plumage is whiter, with less streaking than the common. The “Birds of North America” states they “have been likened to drifting snowflakes and resemble fluffy snowballs when perched.”

Both of these birds are extremely cold hardy, due to behavioral and physiological traits. Their plumage, especially that of the hoary redpoll, is extremely dense and “loose” – meaning it traps a lot of air for insulation against bitter cold.

Each bird also utilizes a specific tactic for obtaining food and conserving energy in the process: When they find seeds, they store them in little pouches that line the esophagus. Later, under protection of dense cover, they regurgitate the seeds, husk them, and swallow them, finally digesting their meals. They conserve a lot of energy in this way.

Still, much is unknown about the common and hoary redpolls. As the BNA states, “Study is particularly lacking in the northernmost parts of its range, where few other birds are able to remain throughout the year. How the hoary can cope with the perpetual darkness of the Arctic winter remains largely a mystery.”

How intriguing. I’d love to find out how these birds survive in such harsh conditions but, at the same time, I want it always to remain a mystery. It’s what keeps me coming back for more.

NEWS bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net