Let's say you wanted to take a census of the number of birds in about one-quarter of the world, at lots of locations throughout that vast area, once a year at the same time, hopefully forever. Oh, and all that data should be compiled in one place and made available to researchers. Logistical nightmare, to say nothing of astronomically expensive and, in a word, impossible!

Nope. The Christmas Bird Count (CBC) is an annual reporting of the numbers and species of birds in more than 2,500 locations in the United States, Canada, the Pacific islands, the Caribbean, and Central and South America, on one day during the period from Dec. 14 to Jan. 5. It's not only done, it's accomplished entirely by volunteer birders and has been for 117 years. The count, a project of the National Audubon Society, is the longest-running citizen science project in the world.

According to the Audubon Society, if those citizen scientists had been paid at average biologist rates, it would have cost more than $5.6 million to amass that data for just one year. Of course, the true value of biological data is longitudinal, so one can see trends over time. The CBC has accumulated millions of dollars worth of information every year for 117 years — for free.

Paying for the data to be tallied, managed, and made available to researchers — a nearly yearlong process — is achieved entirely by donation. With the current administration intent on slashing federal funding for environmental research and conservation, the CBC may even become a model for other scientific projects.

"People like feeling that they're contributing to important science," said Jim Howitz, compiler for both Cedar Creek Bog and St. Paul Northeast counts, who first participated in the CBC in 1980. Because birds are sensitive to environmental changes, CBC data has been used by federal agencies and private researchers to ban the insecticide DDT, track climate change and monitor diseases like West Nile virus and avian flu.

Count circles

Scientists were at first reluctant to rely on data collected by amateurs, but the highly organized structure of the CBC and its attention to detail, documentation and verification holds up to professional standards.

The smallest unit of the massive CBC is a 15-mile diameter count circle identified by longitude and latitude. Each count circle has volunteers, as few as eight and as many as 100, who go out on the same day every year to record the number and species of birds seen or heard in their circle. Those volunteers, usually experienced birders, also record the weather conditions, their location, whether they moved or counted in one spot, their mode of transportation (by car, on foot, by boat, on skis), and the number of hours spent in the field. Normally, volunteers go out between sunrise to sunset, but some may go earlier or later to count nocturnal birds like owls. At the end of the day, all the data is given to the count's compiler, who verifies unusual sightings, and sends it on to the Minnesota Ornithologists' Union and the state CBC compiler.

While it's true anyone can participate in the CBC and most volunteers are not professional ornithologists, they are passionate autodidacts and their skill at identification and counting are honed by year-round practice.

"I'm not as expert as these birders I have," said Laura Coble, who took up birding after a 35-year career in teaching instrumental music and is now the compiler for the Red Wing count. "They've memorized all the common birds — size, shape, song, markings. I love birding with these people. There's so much to learn."

Identifying and counting, by sight or hearing, seem incredibly difficult: How many geese are in that huge flock? Is that the same chickadee you just counted a minute ago? Do hoots from different locations indicate two different owls or the same owl hooting twice? Great horned or barred?

"Counting them as they fly past works well for robins, and waterfowl are easy. Woodland birds are more difficult," Howitz said. Howitz did his doctoral thesis on chickadees and has spent the last 35 years teaching biology and math at Hennepin County Technical College. "Redwings [blackbirds] in Oklahoma and Kansas may number in the millions — there's a technique for that. You can take a photograph, blow it up and count a section, then multiply that by the total area. I find the vast majority of birds by listening. I hear them, then stare in that direction until they move."

Howitz pointed out that complete accuracy isn't really the goal of the CBC but that consistent methods and documentation provide a reliable picture of year-to-year trends.

One of those trends is that, as the average January temperature in the United States increased between 1966 and 2005, at least 20 species have shifted their winter homes farther north. CBC data over the years clearly differentiates a sea change from annual fluctuation and from the occasional bird that has simply lost its way. As a compiler, Howitz has to verify claims of birds sighted where they shouldn't be. "We had a sighting of blue-winged teal which should be thousands of miles south," Howitz said, "but we had a photo, so we confirmed it."

Howitz told a story about a volunteer on the St. Paul Northeast count in the 1980s who reported hearing several great horned owls, which was unusual then. "The compiler at the time thought this guy must have been hearing the same owl over and over or that he'd misidentified it. Shortly after that, the volunteer in question, John Fitzpatrick, moved out to New York and took the top job at the Cornell Lab [of Ornithology]. He's one of the most important ornithologists in the world," Howitz said with a laugh, acknowledging that though this volunteer did not have a photo, his assertions were probably reliable.

Fine-tooth review

Steve Weston of Eagan has been the Minnesota state compiler for the last three years, responsible for tallying the data from the 80 counts statewide, confirming sightings and submitting a detailed report to the Audubon Society. It's this multilevel, fine-tooth review of data that has earned this citizen science project its professional credibility.

"If you see something that's out of place, you'd better take a picture," Weston said of his verification process. "If you can describe it accurately, I'll usually count it. If you can't identify the hawk confidently, we'll put in 'some kind of hawk.' I want to find out that you really know what you saw."

Weston said the number of count circles and volunteers involved in the CBC is increasing, both in Minnesota and program-wide, and because of its funding, it is fairly immune from predation by the Trump administration. The biggest challenge to the CBC, Weston said, is "graying out." Like other traditional outdoor activities like hunting and fishing, the vast majority of birding enthusiasts are older than 50 and white. "A lot of young people have never spent time outdoors and have no interest in it," Weston said. "Where the is future is, we don't know."

Sarah Barker is a freelance writer from St. Paul.