A chill hung in the air and the morning sun flickered through a canopy of cottonwood and willow trees, as Kathleen Blair bent down and began pulling on a pair of hipwaders.

John Rudolf/News-Herald Photos Ecologist Kathleen Blair and volunteer Barbara Todd walk up the Bill Williams River, as part of the Audubon Society’s annual Christmas bird count.

“Are you ready to walk up the river?” she asked.

At dawn on Saturday, Blair, a refuge ecologist with the U.S. Fish and Wildlife Service at the Bill Williams River National Wildlife Refuge, had gathered with about 30 volunteers for the Audubon Society’s annual Christmas bird count, which takes place across North America and the world, at more than 2,000 different locations. The volunteers split up into small groups and fanned out throughout the refuge and along the shores of Lake Havasu, part of an effort to spot as many of the more than 350 bird species known to inhabit the area.

While only about 6,000 acres in size, the Bill Williams refuge is incredibly rich in wildlife, Blair said. “We’re the littlest refuge on the river, but we’ve got more biodiversity than all the others put together,” she said.

Blair led a small group up the Bill Williams River itself, sloshing upstream through ankle-deep water and occasionally hacking through thickets of invasive salt cedar. Joined by husband and wife Barbara and Dick Todd, volunteers at the refuge, the Blairs stopped every few minutes to listen to the whistles and clicks of birds flitting through the trees.

Shallow enough to walk across, the river is nevertheless unique for the state. “This is a live river in Arizona,” Blair said. “It’s one of the last ones left.”

Created by the merging of the Big Sandy and Santa Maria rivers, and held in check by the Alamo Dam, about 40 miles upstream, the Bill Williams river is one of only two tributaries that flow into the Colorado River below the Grand Canyon. Its flow sustains one of the last remaining stands of native willow and cottonwood trees along the Colorado River, vital habitat for a variety of species that are found virtually nowhere else.

Those forests once formed a corridor 280 miles long and several miles wide, all along the length of the Colorado River. But beginning with the construction of Hoover Dam in 1933, most of these forests were either drowned under reservoirs, or dried out and destroyed by the lack of water.

“That forest is now 99 percent gone,” Blair said.

What remains is sustained by the flow of the Bill Williams River, which peaks in the winter and swells in times of flood, bringing vital water to the fertile land and allowing new stands of willow and cottonwood to be seeded.

“It’s amazing out here,” said Dick Todd. “You just add a little water and watch it grow.”

Todd has helped to plant saplings after a devastating fire over a year ago, started by burning diesel fuel that spilled from an overturned tanker truck on Highway 95.

While many native species still survive in the refuge, some of the most spectacular creatures are gone for good from the banks of the river. When the Parker Dam was built in 1938, it drowned not desert but the forest and grasslands of the Chemhuevi Valley, where wild turkeys and prong-horned antelope roamed on land and river otters swam and hunted in the water.

“It was one of the richest, widest valleys around, and now it’s all underwater,” Blair said. “The forests have either been drowned by the dams or replaced by agriculture or cities.”

By early afternoon, the team had spotted red-tailed hawks, woodpeckers, warblers, ravens, and dozens of other species. A full accounting would have to wait until that evening, but Blair was sure it would include many species that had almost been erased from the history books.

“Now the birds that were closest to extinction on the Colorado River are some of the most common birds we see here today,” she said.