Regularly irregular or irregularly regular? I can’t decide.  I’m musing on the most enigmatic of our winter visitors, Bohemian Waxwings.

This species is one of a hodgepodge of species that stage irruptions into Maine from more northerly areas, presumably driven by food shortages. This group of birds also includes Red-breasted Nuthatches, Northern Shrikes, Snowy Owls, Great Gray Owls and a number of northern finches.

Bohemian Waxwings were nearly as scarce as hens’ teeth on Maine Christmas Bird Counts this year. I did not lose hope as I know that we usually get some of these gorgeous birds in Maine by the end of the winter.

On February 4, John Wyatt reported a flock of 2,000 Bohemian Waxwings over his house in Winterport.   He photographed the flock so we know his count is accurate.

Learning of John’s report, I stepped up my vigilance for spotting some waxwings.  With the abundance of ornamental fruit trees on campus, Colby College is a magnet for the fruit-eating Bohemian Waxwings.  Walking across campus on February 18, I heard the buzzy calls of waxwings.  The first two I saw were Cedar Waxwings but I quickly found some Bohemians in the small flock enjoying a meal of crabapples.

I was not prepared for the explosion of birds from the tops of several conifers.  The massive flock, at least 2,000 birds, took flight with a whirr of wings.  It was by far the biggest group of Bohemian Waxwings I have seen on campus over the past 25 years.

When the Bohemians will arrive and how many will appear are unpredictable. The best we can say is that at least a few will arrive in Maine at some point during the winter.

Where do the waxwings we are seeing now come from?  Bohemian Waxwings nest in Alaska and northwestern Canada, nesting as far east as Manitoba.  When they fail to find sufficient food on their nesting grounds, the birds are forced to move to find sufficient food.

Most irruptive species seem to move primarily along a north-south axis.  That pattern makes sense as the distance to travel to more moderate climates is minimized.  But Bohemian Waxwings have a strong longitudinal component of their migration, flying further in an east-west direction than in a north-south direction.  Another aspect of their enigmatic nature.  Perhaps greater fruit abundance in the east explains the pattern.

During the winter, Bohemian Waxwings rely almost exclusively on soft fruits. Such fruits consist of a lot of water so a waxwing needs to eat many fruits to acquire enough fuel to maintain its metabolism.

Of course, fruits are usually frozen solid in the winter.  Melting the fruits has to be a strong energy sink.  To raise the temperature of a gram of ice one degree Centigrade requires one calorie of heat. But to convert a gram of ice at 0 degree C (the freezing point) of water to a gram of water at 0 degrees C takes a whopping 80 calories of heat.  This heat, called the latent heat of fusion, is require to change water from a solid to a liquid state.  Waxwings melt a lot of fruits in the winter.

How can one tell a Bohemian Waxwing from a Cedar Waxwing?  Both species can occur in Maine in the winter so confusion is possible.  Bohemians are grayer than Cedar Waxwings.  Even more useful are the white and yellow marks in the wing of a Bohemian, which are lacking in Cedars.  Finally, the undertail coverts of a Bohemian Waxwing are cinnamon in color, contrasting with the gray underparts.  The undertail coverts of a Cedar Waxwing are white.  Since waxwings are normally found perched in trees, the view of the undersides is the typical view for a birder.  A quick glance at the undertail coverts clinches your identification.