On Christmas Day in 1900, twenty-seven men in twenty-five locations across the United States and Canada went out to count birds instead of shoot them. Frank Chapman, an ornithologist at the American Museum of Natural History, had proposed the idea in the December issue of his journal, Bird-Lore.
Chapman called it a Christmas Bird Census. The point was to substitute observation for sport. The holiday side-hunt — a competitive shoot in which teams tallied as many birds and mammals as they could kill in a single day — was still common in 1900, and Chapman wanted an alternative.
Twenty-five locations was a modest beginning. The 126th count, completed this past December, included over two thousand five hundred individual counts across forty-two countries and territories, conducted by more than eighty thousand participants. They reported approximately fifty-eight million birds.
The method has barely changed.
Each count covers a circle exactly fifteen miles in diameter — a tradition that has now outlasted the imperial system in most of the world but persists because changing it would break continuity. Within each circle, teams divide territory, walk or drive prearranged routes, and tally every bird they identify, by species, between dawn and dusk on a single day in the count period, which runs from December 14 to January 5.
The discipline of the method is its strength. A circle counted in 1955 is the same circle counted in 2025. The route may differ slightly. The participants certainly do. But the spatial unit and the temporal window are constant, which means the data are comparable across three quarters of a century.
That comparability is what makes the count scientifically valuable. The National Audubon Society's 2019 analysis using CBC data identified three hundred and eighty-nine North American bird species at risk from climate change. The work was possible only because someone, in nearly every count circle, had been showing up every December for decades.
The Sapsucker Woods circle in Ithaca, New York, where this magazine is based, has been counted every year since 1939. The compiler position has passed through eight people. The route has been revised three times to account for new development. The mid-day lunch break has always been at the same place, the small lodge at the edge of the pond, which is now part of the Cornell Lab campus.
Counting is harder than it looks. A circle of fifteen miles is over a hundred and seventy square miles. Most circles cover more habitat than any one team can survey thoroughly in a winter day. Compilers spend weeks planning routes, recruiting participants, and assigning territories to people who know the local hotspots.
The participants are not, usually, trained ornithologists. They are retired teachers and software engineers and high-school students and farmers and one nun in Indiana who has counted the same circle for thirty-one years. They wear too many layers. They drink coffee from thermoses. They argue at the compilation dinner about whether the bird at the third stop was a pine siskin or a goldfinch.
The compilation dinner is part of the tradition. After the count, participants gather, usually at a community centre or someone's house, and read through the day's species list. The numbers go up on a whiteboard. Disputes are settled by the compiler, who has the final authority. The dinner is potluck. The conversation is loud.
What the data have shown is mostly grim. The 2019 Audubon analysis, drawing on CBC and Breeding Bird Survey data, estimated that North America has lost approximately 2.9 billion birds since 1970 — a thirty percent decline. The losses are heaviest among grassland species and migratory passerines. They are not evenly distributed across taxonomic groups, regions, or habitat types, and the CBC's spatial coverage has been critical in identifying where the declines are sharpest.
Some categories have done better. Raptors, broadly, have recovered since the banning of DDT. Bald eagles, once rare on most counts, now appear in the thousands. Waterfowl, owing to the long-running Duck Stamp programs that fund wetland conservation, are largely stable or increasing.
These are not victories that can be claimed for the count itself. The count documented them. The conservation work — legislative, scientific, on-the-ground — produced them.
There is a smaller, harder-to-measure benefit of the count that I find myself returning to. People who participate in a Christmas Bird Count tend to keep participating. Some come back for forty years. They learn the circle. They notice when a species disappears from a road they have walked every December.
That kind of attention does not appear in the published analysis. It appears in the compiler's notes, in the conversations at the post-count dinner, in the long memories of the people who count.
The Hilo, Hawaii circle has counted iʻiwi every year since 1968 and noticed, well before the published literature confirmed it, that the species was retreating up the mountain as avian malaria spread. The participants saw the retreat happen.
The Lubec, Maine circle has watched eider numbers fluctuate with the lobster industry's effect on the local invertebrate community.
The Cape May circle, which often produces the highest single-day species totals in the world, has documented the slow recovery of merlin populations across the Atlantic flyway.
These observations are not glamorous. They are not announced at press conferences. They accumulate, year by year, into a record that is unmatched in any other branch of zoology.
Frank Chapman died in 1945. He lived to see the count expand to over a thousand circles. He would not, I think, have predicted that 126 years later, eighty thousand people would still be going out on a December morning to count birds. He would, I hope, have been pleased.
There is something defiantly old-fashioned about it. A clipboard, a pencil, a thermos, a fifteen-mile circle defined by a compass on a paper map. The data eventually go into a national database, which feeds peer-reviewed papers, which feed policy. But the count itself remains an unmediated thing — a person, in a place, paying attention.
Which is, in the end, what citizen science is.
