The invasion has begun. Around March 20, flocks of bohemian waxwings appeared in Maine. What a joy it was to have a flock of 100 in our yard. We are hardly alone; flocks are present across the state.

We have two waxwings in Maine: the cedar waxwing that nests here and the bohemian that is a winter and spring vagrant. Sometimes, cedar waxwings overwinter so we can be blessed with both species of waxwings on a winter’s day. The two species often comingle in a single flock.

Bohemian waxwings belong to a group of birds called irruptive species. These are birds that occur to our north but may in some years be forced south into Maine or farther south in search of food.

The best-known irruptive species are finches like common redpoll, pine siskin, evening grosbeak, pine grosbeak, red crossbill and white-winged crossbill. The seed availability for these birds must have been pretty good to our north because Maine had very few of these irruptive birds this winter except for a moderate flight of red crossbills.

Red-breasted nuthatches are also an irruptive species. We do have a breeding population in Maine, but their numbers are greatly increased in some winters by vagrants from the north.

Snowy owls, great gray owls and northern hawk owls are yet more irruptive species. Their irruptions are not very frequent and involve relatively few birds.

Finally, aptly named bohemian waxwings clearly are irruptive species. In some years, they invade in November and December and are well represented on our Christmas Bird Counts. Even when they fail to appear in the winter, we can usually count on an influx of birds in March, with some persisting into early May.

Bohemian waxwings nest in northwestern Canada into Alaska. Like cedar waxwings, bohemians are fruit-eaters. We know that fruit production by winterberries, crab apples and other fruit trees varies widely from year to year.

After the nesting season, flocks of bohemian waxwings wander in search of fruits. The fruits can be depleted quickly so the flock must keep on the move. They move southeastward, ultimately arriving in northeastern North America, including northern New England.

To find bohemian waxwings, check out areas with large plantings of ornamental fruit trees. The Colby College campus in Waterville and the University of Maine campus in Orono are particularly good, although any tree with hanging fruit will attract these waxwings.

In his “Birds of Maine,” published in 1908, Ora Knight reported that bohemian waxwings had not occurred in Maine for years. This observation was echoed by Ralph Palmer in his 1949 book, “Maine Birds.” These waxwings staged invasions of Maine every two or three years in the 1970s. Since then, they can almost be considered an annual vagrant. We do not have a good handle on why bohemian waxwings have increased as winter visitors over the last 120 years. I just consider us lucky to have them around more often.

Waxwings have wonderfully silky, soft plumage. You can appreciate that with a close-up view through your binoculars or spotting scope.

Distinguishing a bohemian waxwing from a cedar waxwing can be daunting to the uninitiated but is straightforward with a decent look. The two best characters are the cinnamon undertail feathers of a bohemian. In cedar waxwings, those feathers are white. The wings of a bohemian have white patches; a cedar lacks those patches.

Bohemians are slightly larger and grayer than cedars. Their buzzy call is pitched slightly lower than cedars.

Have you ever wondered why waxwings are so named? If you look carefully at the tips of the secondary wing feathers of a waxwing, you can see red deposits. Those structures look a bit like wax but are obtained from the red pigments of fruits the birds eat.

The size and number of the waxy tips increases with age. This feature allows females to choose older males as mates, who generally make better parents.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu

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