The three women walk with careful deliberation, stopping at the piercing sound of a blue jay overhead. "Three blue jays," Evelyn Ralston, a cell biologist, says as she looks up.
Linda Friedland, a retired teacher, nods in confirmation, marking it on their tally sheet.
It's just after sunrise on a December morning in Poolesville, Maryland, and Ralston, Friedland, and Jennifer Kawar are busy counting birds. They're part of the Seneca Christmas Bird Count Circle, and among the three of them, they have more than 30 years of collective birding experience.
For the past 115 years on Christmas Day, people like this Maryland trio have peered through the trees with binoculars and listened for one collective purpose: to count birds.
Birders, scientists, enthusiasts, and students are among the 71,000 observers who have participated in Audubon's annual Christmas Bird Count (CBC), one of the largest, longest-running citizen science efforts in the world. (See "New Report Highlights Dire Situation of Many U.S. Birds.")
The annual event provides important data about bird population trends and helps inform conservation efforts.
Historic Christmas Count
The first count began on Christmas Day in 1900, when Frank Chapman, an ornithologist at the American Museum of Natural History in New York, proposed it as an alternative to hunting birds on Christmas.
Twenty-seven people in 25 different locations across the continent participated that first year and counted about 90 species. (See National Geographic's amazing bird photos.)
Today the Christmas Bird Count takes place annually from December 14 to January 5, and typically more than 30,000 people worldwide count over 2,400 species—about 65 to 70 million birds each year.
Last year's 114th Christmas Bird Count was a record high year, with 2,408 circle counts submitted to the database. (This year's 115th count is still being tallied.) A single birding circle is 15 miles in diameter, and the circle is then broken up into smaller sectors.
As a citizen science effort, "the Christmas Bird Count is the great granddaddy of them all," says Audubon Society Christmas Bird Count Director Geoffrey LeBaron.
The great majority of CBC circles are in the U.S. and Canada, especially in the Northeast; the Washington, D.C., metropolitan area; the California coast; and the Gulf Coast of Texas, where major bird populations exist.
In 1972 the Christmas Bird Count expanded to include counts in Latin America. Today about a hundred circles are counted in countries including Mexico, Colombia, and Costa Rica, where multi-day ecotourism festivals celebrate the count. (See "Climate Change May Put Half of North American Birds at Risk of Extinction.")
While an average circle in the U.S. identifies 85 bird species, a total of 660 to 680 species are usually tallied in the U.S. and Canada. With the Latin American neotropics added, the diversity of species can jump to more than 2,400 species total.
"With Birds, You Forget About Your Worries"
As the three Maryland birders move down the road, notes of different birds blend together. "Ooh, that is a weird little sound," Friedland says. "I hear a soft trill. And a woodpecker, tap tap."
Sounds are welcome riddles for birders, who eagerly decipher the species behind each note. The high-pitched whistle of a white-throated sparrow redirects the group's eyes eastward. Then back down, as a white-breasted nuthatch walks swiftly along a branch. The sparrow sings again. "He did the whole repertoire for us," Kawar, also a retired teacher, says.
Back at the car, the trio stops for a mid-morning snack. Kawar pours steaming English tea into bird mugs, and Ralston and Friedland pass around European cookies. "It's a birder's tailgate," Ralston says.
As they head down another road, Friedland reacts with excitement to a sound coming from the bushes. "A warbler!" she says. "A good add!"
"The rarer the bird, the more excited we get," Ralston says. (Explore National Geographic's backyard bird identifier.)
Friedland starts a sound called "pishing," which mimics a sound birds make to warn each other to mass together as a defensive strategy, Ralston explains, as more birds pop out from the brush. "Some birds are more pishable than others," she says.
In addition to vocalizations, birders rely on markings and flight patterns for visual-identification clues. Woodpeckers and nuthatches, for example, can be identified by their up-and-down, undulating flight.
The women spot six white-crowned sparrows in a driveway. "What a treat," says Kawar, who watches with interest as the group of birds busily peck at the ground. A few junco birds try to start a fight with the sparrows.
"With birds, you forget about your worries," Ralston says. "You're with friends, breathing fresh air."
Doing the Numbers
Their group data will be compiled at a "tally rally" that afternoon by the circle compiler. CBC data have directly helped conservation efforts to protect birds, including American black ducks, after a decline was noted in the bird's wintering populations in the 1980s. (See "The 1,300 Bird Species Facing Extinction Signal Threats to Human Health.")
"It's a lot easier to address threats to a species before it gets critically endangered," says LeBaron. "It's easier to study them because they're out there more, and it's not as expensive to find them. It's an early warning report."
Using CBC data, along with other surveys including the North American Breeding Bird Survey, Audubon now produces a Common Birds in Decline report. The report documents bird population trends over time, including impacts from development, deforestation, land conversion, and climate change.
The Christmas Bird Count methodology has also influenced how other citizen science data sets are collected, says LeBaron, including butterfly, astronomy, botany, and tropical reef counts.
"We're always a team," says Linda Friedland. "You have more eyes, more ears. You never stop learning."
Christy Ullrich Barcus is the editor of National Geographic Polar Bear Watch.