At the turn of the twentieth century, one common way to spend Christmas Day in North America was to walk into the woods with a gun, and see who could shoot the biggest pile of birds and small mammals by nightfall. The winner was whoever killed the most. It was called the side hunt, and it was a holiday tradition.

Frank M. Chapman, a bird expert and one of the early figures in the young Audubon movement, had a different idea. On Christmas Day 1900 he proposed a “Christmas Bird Census”: instead of shooting birds, count them. That first count drew 27 birders who held 25 counts in places from Toronto down to Pacific Grove, California, and tallied around 90 species between them.

The habit stuck. It has happened every winter since, which makes it, as far as anyone can tell, the oldest continuously running count of its kind.

A quick note before we go further: we are not ornithologists or climate scientists, and this is reading and reflection on other people’s work, not expert analysis. The studies we mention draw patterns from large datasets, and a continent-wide pattern is not a prediction about any one backyard.

How a winter habit became a dataset

The setup has stayed simple. Each count happens inside a 15-mile-wide circle, led by a volunteer who organizes everyone who shows up, and it all runs in a fixed window from December 14 to January 5. Do that in one place for a few years and you have a local record. Do it across a continent for twelve decades and you have something no research budget could have bought on purpose.

Nobody in 1900 set out to build a climate baseline. They were looking for a gentler way to spend a holiday. But because the count kept happening, year after year, in roughly the same places at roughly the same time, it slowly turned into one of the longest environmental records we have. Dr. Janet Ng, a wildlife biologist with Environment and Climate Change Canada, put its scale plainly when she called it “the longest in the world, starting from 1900, there’s nothing else like it that exists” among community bird counts.

The scale now is hard to picture. The 126th count, run in the 2025–26 season, spread across more than 2,800 circles reaching from Canada to Chile. Dr. Elizabeth Gray, the CEO of the National Audubon Society, described it as “one of our most important traditions and a wonderful opportunity for people to gather in the name of conservation”. That framing, gathering rather than measuring, is worth keeping in mind, because the people involved mostly think of themselves as birders on a winter walk, not as data collectors.

What 126 winters actually show

The data those winter walks produced has fed real science. Audubon says the records have been cited in more than 300 peer-reviewed articles. Two themes come up again and again.

The first is movement. Geoff LeBaron, who directs the count for Audubon, has said that “there is a northward march of many of the more southern species”. An Audubon analysis of forty years of count data found that 58 percent of 305 widespread wintering species had shifted significantly north since 1968, some by hundreds of kilometers. Scientists working the count have watched some ranges creep north by as much as 200 miles.

The second theme is more troubling. The count was one of several monitoring networks behind the 2019 study in Science by Ken Rosenberg and colleagues, which estimated that North America has lost about 29 percent of its birds since 1970, close to 3 billion birds over roughly five decades. Rosenberg described it as “Multiple, independent lines of evidence show a massive reduction in the abundance of birds”. What made that paper land was where the losses turned up. He noted that “But for the first time, the results also showed pervasive losses among common birds across all habitats, including backyard birds.” Not just the rare and the specialized. The sparrows outside the window. The study added an important caveat: a few groups, including raptors and wetland birds, actually gained ground. So this is a net decline, not every species falling everywhere.

Why people with binoculars still matter

You might expect a century of tradition to be brushed aside by satellites and automated sensors by now. It hasn’t been, for a dull but good reason: the count keeps producing usable data because ordinary people keep showing up in the cold.

The people running it are frank about the limits. Turnout wobbles, hours in the field vary, skill levels differ, and the circles were never placed at random. This is not a laboratory. It’s a loosely standardized census run by whoever turned up.

And yet it works, partly because it is so old. Random ups and downs that would wreck a five-year study start to wash out across a hundred winters. The count doesn’t need any single day to be perfect; it needs to keep happening, and it has. The value isn’t in the precision of one circle on one morning. It’s in the repetition.

There’s something to admire in that. A record this deep didn’t come from a grand plan or a large budget. It came from a modest swap made in 1900, guns for binoculars, and then from people choosing, every December since, to spend a cold morning writing down what they saw. If you have ever wanted to be part of a piece of science without a degree in it, this is about as open a door as the field offers. You count birds. You send in the list. A century of other lists is waiting to give yours meaning.