The Great Backyard Bird Count — a joint project of the Cornell Lab of Ornithology, the National Audubon Society and Bird Count Canada — started Feb. 12, and by 7:40 a.m. Feb. 13, amateur bird-watchers had submitted 7,600 checklists, representing 458 species and more than 800,000 individual birds.

Local birdwatcher Seth Benz checked the figures before he went out Feb. 13 to do his own counting from the Belfast footbridge, a location he chose to draw attention to the four-day event.

“That’s this morning,” he said. “By Monday when this thing ends, these figures will be astronomical.”

Benz, who was director of the Hog Island Audubon Camp for 10 years, does his own counts in Belfast, once a week, from mid-December into March. Toward the end of winter the bay is full of migratory birds waiting for the ice to go out of the ponds and lakes in the area. It was in March or April that he once counted 23 loons.

The process of counting birds is not cumulative at first. The tally on any one person’s checklist derives from the greatest number of birds counted at any one time. “So if you were watching from your backyard and you saw two chickadees at 10:30 and two more at 11, and then three at 12,” Benz said. “the maximum is three, because that’s all you saw at one time.”

From these observations, participants submit a checklist, at which point, the totals are added to those from other checklists, then cataloged by state and municipality.

A cursory look at past Belfast statistics shows a preponderance of herring gulls. Last year there were 3,400 reported in Belfast. On Saturday, Benz and fellow birders Steve Wickenden and William and Kyle Nichols, who are brothers, counted 1,500 herring gulls, nearly all of them crowded onto the roof of the Penobscot McCrum potato-processing plant on nearby Pierce Street. From atop Veterans Memorial Bridge, Benz said, a person could look down at the roof and almost count them individually, but from the street-level footbridge counting would have been tricky.

Fortunately for the bird watchers, every so often a predatory bird would pass by and the gulls would decamp from the roof en masse, causing a sort of ornithological blizzard above the bay.

When there are hundreds of birds in the air, Benz said, it’s possible to count them by estimating how many are in a portion of the sky, then multiplying that figure by an estimate of how many similar-sized portions of the sky are occupied by the same density of birds. Or something like that.

It’s imprecise. At one point, Benz walked over to a white board on which the group had listed a dozen species of birds — each followed by the greatest number of those sighted at once — and added a “1” in front of the entry for herring gulls, changing the total from 500 to 1,500.

Many of the species noted by Benz and company were visible throughout the morning, either in the sky or on the water. The bald eagle that sent the gulls into the air was making lazy circles over the bay, some of the gulls had returned to the factory roof. Mallards and black ducks traveled along the west edge of the Passagassawakeag River, and a single loon, looking nondescript in its gray winter plumage, bobbed near one of the massive supports of the Route 1 Bridge.

“It’s not like they’ve got a sign around their neck,” said Wickenden. “But you get tuned into it and it’s like, ‘We’ve got that all around the bay.'”

Unusual sightings Feb. 13 included eight Barrow’s Goldeneyes, a medium-sized diving duck with a distinctive white crescent between its eye and bill. Benz described this as a “Belfast winter specialty bird.” The birders also saw three Iceland gulls, which they identified from among the throng of herring gulls by their all-white wings.

A checklist from the Great Backyard Bird Count Web site lists 100 species that are likely to be seen in Belfast in February. On the final day of the bird count, 37 had appeared on checklists submitted by a dozen participants.

Data from past years shows a wide range in the number of any given species reported in one year. But according to Pat Leonard of the Cornell Lab of Ornithology, these variations are less important than the larger trends.

“It’s mainly to compare presence and absence,” she said. “… If there’s a huge change over many years, or if a certain species disappears.”

Leonard chalked up the variations in GBBC statistics to the reporting protocols, which she said are less strict than those of the hundred-year-old Audubon Christmas Bird Count.

“We don’t ask for a high level of expertise,” she said. “We just ask that if you don’t know a species of bird that you don’t try to make something up.”

The final report from the Christmas Bird Count arrives nine months after the results are in, Benz said. “With this [the GBBC], the idea was you could get people of any age — classrooms are doing this — and they can post and see their results immediately, the idea being you can see yourself contributing to a real scientific effort.”