Saturday, May 18, 2013
By Herb Wilson
Evening grosbeaks, one of the most enigmatic and erratic of our winter finches, have been appearing across Maine this fall. We had a dozen of these beauties at our sunflower feeders in China a couple of weeks ago. Maybe these birds are harbingers of a much-anticipated irruption into New England.
These robust, colorful birds add welcome color to the muted fall and winter landscapes in Maine. The males, with their yellow bodies, brown heads with yellow eyebrows and a large patch of white on each black wing, are stunning. The understated females, with tones of bluish-gray on their body and a large white patch on each black wing, have a beauty of their own. Evening grosbeaks are conspicuous, usually announcing their presence with metallic "cleep" notes, reminiscent of a house sparrow's call. They love sunflower seeds, so keep your feeders stocked.
The scientific name of this finch is Coccothraustes vespertinus. The genus name Coccothraustes means "kernel breaker," certainly appropriate for this bird with a stout, conical beak. The species name vespertinus refers to "evening," a puzzling claim since these birds are active all day long, as anyone lucky enough to have them at a feeder can attest.
The evening reference comes from observations made by a Major Delafield, a United States boundary agent in 1823:
"At twilight, the bird which I had before heard to cry in a singular strain, and only at his hour, made its appearance close by my tent, and a flock of about half a dozen perched on the bushes in my encampment . . . My inference was then, and is now, that this bird dwells in such dark retreats, and leaves them at the approach of night."
Obviously, Delafield was not a very good field naturalist. We know that evening grosbeaks go to roost around dusk like any self-respecting perching bird. Nevertheless, Delafield's observations were taken seriously by subsequent scientists who dubbed Coccothraustes vespertinus the evening grosbeak. I think evening grosbeak is the most inaccurate common name of any North American bird, beating out ring-necked duck.
Evening grosbeaks are relatively recent arrivals in Maine. The great Massachusetts ornithologist, Edward Forbush, claims that until the winter of 1889-90, evening grosbeaks were virtually unknown east of Ohio. During that winter, an eastward invasion brought these birds into Massachusetts, nearly as far east as Boston.
A second large invasion came in 1910-11, leading to the gradual establishment of evening grosbeaks as breeding birds in southeastern Canada and northeastern United States.
Some have suggested that the immigration of evening grosbeaks into the east was facilitated by the spread of box elder (Acer negundo) trees. The seeds and buds of box elders are highly favored by evening grosbeaks. The planting of these trees as ornamentals may have permitted the invasion of evening grosbeaks to Maine.
Evening grosbeaks nest throughout the state, but their numbers vary erratically from year to year and from place to place. Winter numbers rise as individuals from more northerly populations come into Maine and further south in numbers that vary widely from year to year.
Highly gregarious outside of the breeding season, evening grosbeaks have a hierarchical social system where males, which are larger, are dominant to the smaller females. These interactions can be easily seen at a feeder. Research by David Prescott showed that female evening grosbeaks tend to migrate farther south than the males. Prescott proposed two reasons to explain this differential migration. First, the subordinate females may be forced farther south because of the dominant males. Alternatively, the larger males may better able to withstand cold temperatures.
In any case, count the number of male and female evening grosbeaks this winter. If Prescott's pattern holds true, you should see a predominance of gaudy males here in Maine.
Herb Wilson teaches ornithology and other biology courses at Colby College and perches in South China. He welcomes reader comments and questions at: