As I was leaving work the other day I heard the unmistakable calling of waxwings. It took me a few seconds to locate them; surprisingly, they were perched in a crabapple tree right behind me. Their call notes were so faint and high-pitched it sounded as if they were far away.

The birds were cedar waxwings and I stared at them, amused but puzzled. These birds usually occur in flocks during the winter, but here there were only two of them. They continued to make their high, lisping calls as they stared right back at me. I continued on my way, not wishing to disturb them.

Waxwings are so named because of the red, wax-like tips projecting from the ends of their secondary flight feathers. Ornithologists think these tips are related to the breeding condition of the bird: they are more numerous and more prominent on mature birds.

Two kinds of waxwings inhabit North America: cedar waxwings and bohemian waxwings. The cedar breeds across most of the United States, to about midcontinent, and up into Canada; the bohemian is primarily a western bird, breeding in Alaska and northwestern Canada across to Hudson Bay.

According to the “Birds of North America” species accounts, both birds are known to travel widely in response to the availability (or lack) of their winter food of fruit. However, the bohemian (meaning “vagabond” or “gypsy”) is known to wander far, far outside its range, regularly reaching the northeastern United States and Canada. Birdwatchers here in Maine expect this bird every winter.

In contrast, cedar waxwings tend to have more regular patterns of migration, although they will also wander widely in search of the winter fruit. Cedar berries, crabapples, and mountain ash are some of their favorites.

I learned some fascinating things about these birds in the BNA species accounts. For instance, because they depend on ephemeral, unpredictable food sources, they tend to be a lot more social with each other. In winter they gather in large flocks, sometimes numbering in the thousands. During the breeding season, when other birds become aggressive and territorial, waxwings remain sociable, even nesting near one another.

In addition, waxwings time their breeding cycle to coincide with the ripening of summer fruiting trees and shrubs, such as serviceberry, strawberry, mulberry, and cherry, although at this time they supplement this diet with insects. Consequently, while other birds are feeding growing nestlings and beginning to fledge their young, waxwings are just getting around to egg laying.

How to tell these two birds apart? For me, the most reliable field mark is the color of the undertail feathers, or “coverts.” Cedar waxwings have whitish undertail coverts; bohemians have deep chestnut undertail coverts. As long as the light is good, even from a distance there is no mistaking them (as long as you have a decent pair of binoculars!).

Another telling point for me is voice. It seems to me that bohemian waxwing call notes are louder and burrier: “brrrddeeee.” Cedar waxwing notes are cleaner, higher-pitched, and more whistle-like: “seee, seee,” or “bzee, bzee.”

It is always a treat to see these winter visitors, but I’ll happily say goodbye till next year in favor of spring’s returning migrants.

Chris Corio, a volunteer at Fields Pond Audubon Center in Holden, can be reached at fieldspond@juno.com