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 as well) they could. At the end of the day, each side would pile up all the animal carcasses they had collected. The team with the bigger pile was declared the winner. If you are like me, you regard this practice as barbaric and senseless.

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 on Christmas Day 1900. Twenty-five counts and 27 birders conducted those counts. Most were in the northeastern United States, but Toronto and Pacific Grove, Calif., were covered as well. Collectively, these original counts produced a cumulative list of 90 species of birds.

A standardized method for conducting Christmas Bird Counts (hereafter, CBCs) was established to allow comparisons of counts between different areas. The unit of a CBC is the count circle, a circle with a radius of 7.5 miles from a fixed point. On one day during the national count period (mid-December to early January), observers spread out in a count circle and count all the birds they see or hear in one calendar day. The weather, number of observers and number of hours spent in the field are published on the National Audubon Society’s website (www.audubon.org).

These counts provide a rich source of information on changing bird populations. For instance, the northward and southward expansion of the house finch, introduced into the East in New York City, can be followed by looking at CBCs over the years. Similarly, the northward expansion of red-bellied woodpeckers, tufted titmice, Carolina wrens and northern mockingbirds is well documented. Downward trends sound the alarm that particular species may be in trouble. For instance, harlequin ducks have been declining on CBCs in eastern Canada and are now listed as an endangered species in Canada.

CBCs have become very popular activities, with a particular increase in the number of counts occurring in the early 1970s. For the 2011-12 CBC (the 112th CBC), there were 2,248 individual counts conducted by 63.227 observers. Of these counts, 2,149 were conducted in North America, with the remainder in tropical areas including Central and South America, Bermuda, Hawaii and islands in the South Pacific. U.S. observers counted a total of 60,502,185 birds belonging to 666 species during the 2011-12 CBC. We have come a long way from the days of side hunts.

In Maine, there were 32 CBCs during the 2011-12 count season. These counts ranged from Presque Isle in the north to York County in the south and from Eastport in the east to Sweden in the west.

You do not have to be an expert to participate in a CBC. Some CBCs have already occurred this year, others are yet to take place. You can find a list of all Maine CBCs and their coordinators at maineaudubon.org/wildlife-habitat/christmas-bird-count/. I encourage you to contact an organizer and take part in the fun. Usually the organizer will host a social gathering after the sun goes down for all the participants to have a warm drink, share the day’s memorable sightings and compile the list.

In the first three columns of every 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 and perches in South China. He welcomes reader comments and questions at:

whwilson@colby.edu