The 118th Audubon Christmas Bird Count is under way, ending Jan. 5. The data provides a valuable tool to gauge changes in our winter bird populations.

Four species are found, often abundantly, on most Maine counts: rock pigeon, european starling, house finch and house sparrow. None of these species was present in eastern North America 500 years ago.

Rock pigeons were introduced into North America in the early 1600s, likely to provide a source of meat. Rock pigeons can now be found in urban and agricultural areas throughout the United States.

Starlings were introduced for a quite different reason. A New Yorker named Eugene Schieffelin thought it would be wonderful if he could establish populations of all the bird species mentioned in Shakespeare’s plays in Central Park. He released 60 starlings in 1880 and 40 more in 1881. From those releases, starlings spread across the continent with a population now exceeding 200 million birds.

House finches are native to Mexico and the southwestern United States. In the first half of the 20th century, house finches were illegally brought east and sold as cage birds called Hollywood finches. The colorful males sing readily in captivity. Pet shop owners in New York City and environs caught wind of an impending raid by law enforcement officers and emptied their cages before the raids commenced. From those introductions, house finches have spread across all of the states east and north of the original range. The range of introduced birds overlaps now with the original house finch populations.

House sparrows were introduced in North America in Brooklyn in 1851 and 1852. Subsequent introductions occurred in San Francisco in 1871 and 1872, and in Salt Lake City in 1873 and 1874. Now house sparrows are found throughout the lower 48 states except for southwest Texas.

How to treat introduced birds? Some birders keep life lists in which they do not count introduced birds. Such a birder might report a life list of 311 NIB (no introduced birds) species in the state of Maine.

I think sorting birds into native birds and introduced birds is not a black-and-white issue. I wrote recently about cattle egrets, which reached the New World by dispersing from Africa on their own. Within a continent, birds may expand their ranges. Turkey vultures and red-bellied woodpeckers are good examples for Maine. The avifauna of islands is built almost entirely by birds dispersing from mainland areas.

Should we bother counting pigeons, european starlings, house finches and house sparrows on our Christmas Counts? Absolutely. All four species are well-established members of the Maine avifauna.

All four species interact with native birds. These species are never far from human habitation, so human-friendly native birds are more likely to be influenced by the introduced birds.

As seed-eaters, rock pigeons can be pests. The pigeons readily eat seeds planted by farmers and improperly stored grain. Pigeons may compete with other seed-eating birds like sparrows for natural seeds.

Starlings are cavity-nesting birds and compete with native cavity-nesters like woodpeckers, great crested flycatchers, eastern bluebirds and even the introduced house sparrows.

House finches compete with purple finches and house sparrows. We have pretty good evidence that purple finches are less abundant in proximity to human dwellings than they were before the arrival of house finches. Purple finches are doing fine in large forested areas where house finches do not occur.

House sparrows are cavity-nesters and have deleterious effects on wrens, chickadees and eastern bluebirds.

Like it or not, this quartet of introduced species are important members of our bird communities and deserve our attention.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

whwilson@colby.edu