The flock rose as one and disappeared into the trees as we approached. The combined sound of their wings was distinctive – much louder than what any individual could produce. I could only liken it to that of a large, heavy rug being shaken.

Although we were still some distance away from the birds, I identified them immediately. As they sped into the trees, the white sides of their tails, which are fanned in flight, were readily visible. They were dark-eyed juncos.

Another distinguishing feature of these birds is their color pattern: dark gray above, contrasting at about mid-chest to a startling white below. They bring to mind dark skies over a snow-covered landscape, and have been called “snow birds,” because they often appear at the start of winter.

Juncos are part of the family Emberizidae, and are actually sparrows. Each autumn, they migrate from Canada and the northernmost portions of the country to spend the winter feeding on weed and grass seeds. They are ground-feeding birds, but will also come to backyard feeding stations as long as seed is scattered on the ground or offered on a platform feeder.

In the wild, juncos have an ingenious method of obtaining food from standing grass: They alight at the top of the stem and “ride” it down to the ground as it bends under their weight. They then have easy access to the seed head and eat at their leisure.

Researchers have studied these birds extensively and have found the same flocks return to the same areas each winter. Members follow a strict hierarchy and settle disputes of status with various displays that are easily discerned by the human observer.

Because males do not migrate as far south as females, they are the first to return and defend their breeding territories in the spring. A male’s territorial song is a light musical trill, with distinct differences that enable even a human listener to tell individual birds apart. Once he pairs with a female, they may raise up to two broods a season, producing an average of 3-5 eggs per clutch from a nest strategically hidden on the ground.

This cycle of the juncos’ lives is, alas, several months distant. In the meantime, their musical call notes and stark but beautiful plumage will enlighten many a long, dreary winter day.

Chris Corio’s column on birds is published each Saturday. Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com