Birds on the lam

By Bill Chaisson
Of a Feather
A neighbor of mine recently saw a blue grosbeak at his feeder. Sightings like this are a little disorienting because usually birds are pretty good about staying within the ranges attributed to them in bird guides. The blue grosbeak is not a common bird anywhere and apparently never has been, so seeing one in its accepted range, which on the east coast is from New Jersey southward, is still a good day in the field.

An excellent picture of this wandering grosbeak was posted online. The gray edges on the blue feathers of the bird’s breast and belly suggest it is a young male. David Sibley illustrates a male in its “first winter (August – March)” and it looks very much like a female blue grosbeak, which is to say, not blue at all. These first winter male birds are a “warm rufous-brown overall,” while the females are “paler gray-brown overall.”

The “first summer (March-September)” males have largely blue upper parts (head, back and tail) and a blue bib under the bill and varying patches of blue on a gray-brown chest, according to Sibley. The belly and sides are gray-brown. The bird that has wandered to Sutton, N.H. is fully blue, but the gray edges to the breast and belly feathers perhaps suggest a male in its “second summer,” that is, not fully mature.

Young birds are the dispersers in a population. Their parents ultimately drive them out of the territory where they were born because, after a certain point, they are mere competitors for resources, not beloved children. How far they disperse is likely also a function of resource availability. One of the birds in the collection of sighting records at eBird.org is an obvious young male — its breast and belly is mottled blue and rufous-brown — and it was photographed on Mount Desert Island in Maine, April 28, 2018.

In all the descriptions of blue grosbeak distribution I have read it is noted that although they are very broadly distributed through the southern United States, they are not common anywhere. The allaboutbirds.org entry for this species states that it was thought of as rare even in the 19th century. Its northward spread in the 19th and early 20th century was attributed to the widespread clearing of forests. In addition to expanding its range, the species may even have become marginally more common since the 1960s.

The blue grosbeak has been expanding its range steadily for over a century. In my trusty 1917 “Birds of America” it was described as ranging north “regularly, but very locally, to Pennsylvania, New Jersey, Kentucky, and southern Illinois; accidentally to Maine, eastern Massachusetts, Province of Quebec.” Sibley’s guide (I have the 2000 edition) shows his accidental sightings as green dots and in the Northeast they are scattered across upstate New York, New England and even to Nova Scotia.

“Birds of America” notes that the species has a variable appearance across this range; the blue grosbeaks of the Southwest are paler and more frequently seen near human habitation. In the eastern part of its range, the bird is said to shun suburbia and be most fond of neglected farmland where it prefers to live among “short trees and shrubs,” the more thicket-like the better.

The grosbeak name doesn’t describe a natural group; it is a descriptive term that is applied to birds that have been found to be only loosely related. Several are in the finch family Fringillidae. Thirteen species are in the subfamily Carduelinae. Of these only two are found in North America: the evening grosbeak (Hesperiphona vespertina) and the pine grosbeak (Pinicola enucleator), and these are not closely related to one another.

The family Cardinalidae is confined to the New World and includes 17 species called grosbeaks. Two in the genus Pheucticus have complementary western and eastern ranges, black-headed in the west and rose-breasted grosbeak in the east. The “blue cardinal-grosbeaks” are all found in South America, except for the blue grosbeak.

Molecular systematics has made it possible to discover the true pattern of relatedness among these species, which were formerly classified on the basis of appearance. Using appearance can be confounded by convergent evolution. The conical beak of a grosbeak is adapted to crushing seeds, although many of them feed on insects as well.

The famous example of appearances being unrelated to relatedness is that of “Darwin’s finches” of the Galapagos Islands. It is now understood that they are all part of the South American tanager family, Thraupidae, which is omnivorous. Several of the Galapagos “ground finches,” however, developed extremely conical beaks in order to specialize in seed-cracking, which made them look very finch-like.

The blue grosbeak, then, is not closely related to the rose-breasted or evening grosbeaks. Instead, it has been found to be basically a big bunting. The New World buntings are all in the genus Passerina in the family Cardinalidae (The Old World buntings are in the family Emberizidae). The blue grosbeak was long classified in its own genus Guiraca, but in the massive 2013 reorganization by Keith Barker and others, it was found to be most closely related to the lazuli bunting of western North America, which is in turn closely related to the familiar indigo bunting of eastern North America. The lazuli and indigo buntings interbreed where their ranges meet on the Great Plains.

The blue grosbeak sighting in Sutton this week may just be the result of a lost migrant being blown north by storms. Or it may be range extension. Has anyone seen a female blue grosbeak?

Bill Chaisson, who has been a birdwatcher since age 11, is a former editor of the Eagle Times. He now works for the Town of Wilmot and lives in Sutton.