We are finishing up the 115th National Audubon Christmas Bird Count. This year’s count period began on Dec. 14 and continues until Jan. 5.

Each count occurs on a single day within a circle with a diameter of 15 miles (an area of 78 square miles). The data for all the counts are archived online by the National Audubon Society and are available for download by researchers and birders. I have published four papers that relied partly or wholly on Christmas Bird Count (CBC) data. This database is a remarkable resource for tracking changes in populations of wintering birds in North American and elsewhere.

The timing of CBCs is a bit early to sample winter populations. Depending on the severity of the late fall and early winter, some migratory birds may linger in the area. Great blue herons, northern harriers, belted kingfishers, eastern phoebes, hermit thrushes, eastern bluebirds, gray catbirds, various warblers and even Baltimore orioles fall into this category.

Virtually all of these lingering birds will be long gone by the first of February. On the other hand, the incursion of birds from the north can continue into January and February. The number of Bohemian waxwings, pine grosbeaks, white-winged crossbills, evening grosbeaks, pine siskins and common redpolls we see in late December may be dwarfed by numbers later in the winter. Wouldn’t it make more sense of have a continent-wide winter count in late January or early February? I think so. The initiation of the Great Backyard Bird Count over Presidents’ Day weekend in February does provide deep-winter snapshots of winter bird abundance, although the feeder-bird focus of this count fails to get a meaningful count of winter birds that don’t frequent feeders.

Why then was the decision made to conduct CBCs in late December?

Historical constraints provide the answer. Around the turn of the 20th century, a popular activity in New England towns on Christmas Day was the “side hunt.” The men of the town would divide up into two sides and then comb the countryside and shore, shooting every bird (and mammal) they could. At the end of the day, each side would pile up all the carcasses they had collected. The team with the bigger pile was declared the winner. Most people today would regard such wanton killing as barbaric and unethical. Frank Chapman, an ornithologist at the American Museum of Natural History and a leader of the nascent National Audubon Society, thought so too and offered an alternative. Instead of shooting birds, people were encouraged to go out and count the birds they saw. The counts that people made were then published and served as a record of the bird abundance and distribution for particular areas. Thus was born the Christmas Bird Count.

The first censuses were held in 1900 on Christmas Day. Twenty-five counts were held with modest participation. Most counts were in the northeastern United States, but Toronto and Pacific Grove, California, were covered as well. Collectively, these original counts produced a cumulative list of 90 species of birds.

Now, nearly 2,500 counts are conducted each year. More than 1,800 are in the United States and more than 400 in Canada. The remainder are held in Central and South America, Bermuda, various Caribbean islands and some Pacific islands, including Hawaii.

The CBC database is a testament to the power of citizen science, to the cooperative collection of data by many people with a single purpose. The northward expansion of house finches, red-bellied woodpeckers, northern mockingbirds and the decline of harlequin ducks in the east is evident in the CBC data. We’ve come quite a way since the time of the side hunts.

In three of the first columns of each year, I discuss the highlights of many of the Maine CBCs. You’ll see those columns soon.

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

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