Bluffdale • With a dozen other dedicated birders, Charles Hurd ambled slowly, deliberately Tuesday along the Jordan River.

He peered into reeds, across pastures and over a still-pastoral landscape hemmed by the Salt Lake Valley’s crush of residential and commercial development. The birders occasionally raised binoculars to their eyes and pointed out an interesting avian life form, flitting in a tree or bush or streaking across the horizon.

Voices became excited when an identification was made, often given away by the bird’s coloring, size, shape or even its own vocalization, like that of a rail that refused to reveal its whereabouts in a thicket.

In the case of a northern harrier over a field, it was the bird’s low, erratic flight and silvery glint against a bright cloudless sky.

“The males are gray, the females are brown. It’s called sexual dimorphism,” Hurd said. “They aren’t a hawk or an eagle or an owl. A harrier is a harrier is a harrier.”

Led by Bryant Olsen, a conservation ecologist at Salt Lake City’s Tracy Aviary, this group of birders braved Tuesday’s frigid cold, all in the name of science.

(Francisco Kjolseth | The Salt Lake Tribune) A common goldeneye skips along the waters of the Jordan River recently. A group of Audubon members took to a stretch of the river for the New Year's Day bird count as part of the annual survey, now its 119th year, done by multiple members across Utah.

Olsen’s was one of eight groups counting birds along the Jordan River as part of the Audubon Society’s 119th annual Christmas Bird Count, which is believed to be the world’s longest-running citizen-science project. Naturalist Frank Chapman, then a curator at the American Museum of Natural History, started the count in 1900 as a pushback against yuletide animal-killing festivals.

Back then, birds and other wildlife species were hunted with no thought toward a sustainable harvest or the intrinsic value of living animals on a landscape. Times have changed; now hunting is carefully regulated and the Christmas Bird Count is a huge data-gathering campaign that helps scientists track the rises and declines of various species in particular areas.

“It has become a tradition for birders in the holiday season,” said the Audubon Society’s Geoff LeBaron, who runs the bird-counting program. “People travel all over the country to do a count that got them started. The social component is as valuable as the data. It’s what keeps it going.”

Last year, a record 2,585 counts from North America were submitted, according to LeBaron. These counts documented 59.2 million birds representing 2,673 species, nearly a quarter of the world’s total.

“Adding observations to more than a century of data helps scientists and conservationists discover trends that make our work more impactful,” LeBaron said. This year’s counts are all being done between Dec. 14 and Jan. 5.

For a particular count, the organizer chooses a center point and draws a 7.5-mile radius around it. Groups then spend much of a day counting every bird they see within that circle.

“They are counting every individual bird as well as species,” said Jeanne Lebar, who has organized the Jordan River count since the early 1990s. “We saw 80 species last year. The number goes up and down year to year. What is that? Is it the weather? Is it the number of people looking, the quality of the people?”

(Francisco Kjolseth | The Salt Lake Tribune) A group of Audubon members walk a long stretch of the Jordan River from Bangerter Highway to South Jordan on New Year's Day counting birds as part of the annual survey, now its 119th year, done by multiple members across Utah.

For the Jordan count, Olsen has long led the group surveying the northernmost stretch of river inside the circle that reaches from South Jordan upstream to Utah Lake.

Tracy Aviary has been surveying this area year-round since 2011. Olsen’s team members are all taking the aviary’s citizen-science course, in which Hurd has become famous among his classmates for recording perfect scores when they are tested on bird songs. They learn 10 each week of the 12-week course.

On Tuesday, Hurd was putting his knowledge to work, discerning the song of a hidden sparrow. For these aficionados, the Christmas count is just a warmup for breeding-season surveys.

The team started at the Arrow Trailhead, about 13800 South, and walked along the Jordan River Parkway 4 miles to 10600 South.

Olsen recorded the sightings and occasional soundings in a yellow spiral-bound notebook, in which each species is listed as a four-letter code, like AMRO for the American robin, SSHA for the sharp-shinned hawk or EUST for the European starling. The latter seemed to be everywhere, huddling on tree branches.

One massive group lit out en masse from a stand, too many to accurately count, so Olsen estimated the flock at 150.

“We don’t like starlings,” Olsen said. “They are nonnative. They are invasive. They are abundant. And they are hard to count. The one good thing about starlings is raptors like to eat them.”

As if on cue, a sharp-shinned hawk, or sharpie, as birders prefer calling this agile stalker, sailed across a field, probably in search of starlings or some other small songbird.

Most daytime hunters fly high to get a broad view of open ground that harbors their prey. But not the northern harrier, which is better equipped to search with its ears than with its eyes.

“You know why they are flying so low?” Olsen asked. “You won’t see them perched in trees. They like to be just a few feet off the ground.”

Close to the ground, harriers can pick up the faint sounds that lead to a nice four-legged package of protein and fur.

By 11 a.m., hardly a mile into the walk, Olsen already had 26 species listed in his book. He usually records about 60 species on the Christmas Bird Count, but he said more than twice that number inhabit this area over the year.

This steam zone is layered with conservation easements, anchored by the state’s 250-acre Galena-Soónkahni Preserve, that have held back the onslaught of sprawl that has filled the valley’s south end. Olsen believes this area holds the greatest diversity of bird species outside the Great Salt Lake despite the prevalence of nonnative plants dominating the streambanks: tamarisk, phragmites and Russian olive.

The state Department of Natural Resources, which manages the Galena preserve, has been trying to eradicate these invasives, but Olsen is concerned these plants are pulled out before hawthorn and other native plants can be established, leaving areas devoid of plants and undermining the preserve’s value as habitat.

“Birds aren’t botanists,” Olsen said. “They will use whatever they find for cover.”