OAKLAND — Well before sunrise Sunday, wife and husband team Juli Chamberlin and Bob Toleno were on their way to Lake Merritt, looking for killdeer and owls.

Following in their footsteps that day would be almost 300 other volunteer birders, fellow participants in the Audubon Society’s annual Christmas Bird Count, which attempts to document every bird in the area, providing a snapshot of the state of avian life.

It is one of more than 2,500 count circles organized by the Audubon Society throughout the Western Hemisphere, including about 15 in the Bay Area over a three-week period.

Last year, 76,669 observers counted 58,878,071 birds of 2,607 species, about one-quarter of the world’s known avifauna, according to the Audubon Society’s website.

One of the tricks of the trade is to account for flocks that come and go, Chamberlin said.

“You have to make a judgment call with flocks that move around a lot. You don’t want to overcount them,” she said.

She has been participating in the Christmas counts for five years, and plans to take part in San Francisco’s on Tuesday.

“The more you do it, the more layers you learn. That knowledge collects,” she said.

This year marked Oakland’s 76th Christmas Bird Count. Audubon Society started the counts in 1900 as an alternative to a tradition of a Christmas bird hunting competition, according to the group’s website.

Volunteers register in advance and are divided into groups to scour sections of a 15-mile diameter circle extending, in Oakland’s case, from Lake Merritt to Treasure Island, San Pablo Reservoir to the north, east to St. Mary’s College in Moraga and south to the Oakland airport.

Chamberlin’s team of about five — some birders were available for only part of the dawn-to-dusk count — patrolled the area around Lake Merritt near the Rotary Nature Center. Her husband’s team scoured the waterfront along the estuary.

Other teams dispersed to Sausal and Peralta creeks, and there were two boats of birders deployed as well.

For Chamberlin, the day’s highlight was the sight of a merlin, a small falcon. “It just flew through. You had to be quick,” to spot it, she said. The counters were able to identify it by its flight style, shape and proportions, she said.

“It’s always exciting when you see a bird you didn’t expect. A satisfying moment. You usually have a handful of these when you’re out all day birding,” Chamberlin said.

Also, she said, “there’s a lot of joy in seeing other people enjoy birds and sharing our knowledge,” she said.

Last year in Oakland, 277 field observers and 37 backyard watchers documented 179 species and 96,287 individual birds.

“We won’t have final numbers for weeks and weeks,” said Ilana DeBare of the Golden Gate Audubon Society.

With 90 percent of the teams reporting, the preliminary count was 177 species spotted, DeBare said.

“A lot of the groups recorded lower numbers of birds generally, probably because of the cold weather. The birds may have been hunkered down and not out and about.

“Anecdotally, one of the things that people seemed to be commenting on, and this is not just this year compared to last year, but it’s compared to, say, over a 20-year period, is lower numbers of some water birds, like a kind of duck that’s out on the bay called scaup,” DeBare said.

Other birders noticed the drop in water birds, too. “No loons, no mew gulls, no scoters,” Chad Wilsey said. “One pelagic cormorant.” His team mused over reports of a falcon sighting.

“Must be one of the peregrines that nest on the Fruitvale Bridge,” he said. “What other species of falcon would it be?”

Among the questions this year’s counters had were whether they would see a continued increase in American crows, common ravens and wild turkeys.

Final tallies will be posted online at the Audubon Society’s website, which also has previous years’ results.

Data from the Christmas Bird Counts is compiled and archived by National Audubon Society and the Cornell Lab of Ornithology and made available to the public.

It is used by scientists to track bird populations and see trends that indicate whether certain species are declining or increasing in population. The data was a key resource in a 2014 Audubon Society report on how more than 500 North American bird species would be affected by climate change, DeBare said.

Chamberlin’s group did not spot any owls or killdeer, “but other groups in forest areas were successful.”

Contact Mark Hedin at 510-293-2452, 408-759-2132 or mhedin@bayareanewsgroup.com.