Winter birding is often sparse and touch-and-go. However, certain habitats almost guarantee you’ll see something.

Take bodies of water, for instance. At the very least, you’re likely to see a small group of mallards and observe some interesting behavior in these commonly seen ducks. Or, you could see something more unusual – winter visitors from far away not seen here at any other time of the year: Barrow’s goldeneye ducks.

This medium-sized duck breeds around inland lakes in mountainous areas of western North America, in the Canadian Maritime Provinces, and in Iceland. At the onset of winter and freeze-up it migrates to coastal regions and in Maine can be found on rivers as long as the water stays open.

On a recent cold, clear winter’s morning, my fellow bird enthusiast Ed Grew reported seeing a small flock of the goldeneyes in the Stillwater River.

“Barrow’s goldeneyes apparently hang out below the dam in Stillwater Village. I had a closeup view of five males (four adult, one immature) from the Bangor Hydro parking lot off Free Street. I approached the edge carefully as the river is right below and they could be easily spooked. Very close viewing for goldeneyes, and from above. It’s the first time I’ve recognized an immature male. In general, the immature’s coloration resembles more that of a female, but it shows incipient crescents on the cheeks and lacks the yellow bill characteristic of females.”

The key identifying characteristic of these ducks – at least in the males – is, as Ed mentioned, a large white crescent-shaped patch just in front of the bill. This contrasts sharply with the rest of the head, which appears black, but the right light will bring out its purple iridescence. Its neck, chest, belly, and sides are white, while its back shows a black-and-white checkerboard pattern, reminiscent of the loon, although not as extensive.

Females are less flashy, with grayish-brown plumage over most of their bodies; their heads are entirely brown and lack any iridescence.

A similar duck is the common goldeneye, which may also be found on rivers in winter. Unlike the Barrow’s, it breeds throughout much of Maine and northern North America. In appearance, the key difference between it and the Barrow’s is the presence of a round, rather than crescent-shaped, white patch in front of the male’s bill. It also does not have the checkerboard pattern on its back, instead exhibiting a delicate pinstripe coloration with fewer black feathers. Females of both species are almost identical.

The Barrow’s goldeneyes Ed observed below the Stillwater dam were busy diving for food, such as mussels and fish.

“When foraging, they dive frequently, making identification more difficult,” Ed observed. “Today, fortunately, they were not diving so frequently as usual.”

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