When an aquatic ecologist was surveying shallow lakes in Northwest Alaska three years ago, she and the pilot who traveled with her came upon an unusual sight in the treeless Arctic region: a pair of terns that kept flying around and perching on what appeared to be a log sticking out of a muddy area.

The protruding object, it turns out, was no log. It was the large and well-preserved leg bone of a woolly mammoth. Right by it was another bone, perfectly articulated, that was clearly from the same leg.

"It was like the mammoth just (lay) over there," said Amy Larsen, the National Park Service ecologist surveying the site in Bering Land Bridge National Preserve.

Other remains spotted by Larsen included some mammoth teeth and, in the muddy area created by lake drainage, the curling outlines of two tusks.

The leg bone that sparked the artifact search was likely pushed around in the soil over the millennia until it wound up in the unnamed lake, said Jeff Rasic, a Fairbanks-based National Park Service archaeologist.

"This bone was probably frozen for thousands and thousands of years, until very recently," said Rasic, who traveled to the site later that summer with colleagues and found 13 separate bones.

Analysis of a tooth and other samples dates them to about 14,000 years ago, Rasic said. That makes them some of the youngest mammoth remains discovered in Alaska, he said.

More striking, he said, was that the bones discovered match each other and seem to be from a single animal, he said.

Now, new information indicates there are far more mammoth bones in the lake, raising hopes that an entire skeleton will be found, or close to an entire skeleton. That would be a first for Alaska, Rasic said.

He returned last month to the lake, and with him was Thomas Urban of Cornell University, an expert in near-surface exploration geophysics.

Rasic and Urban moved across the still-frozen lake surface and searched with a radar device for objects below. In all, Rasic said, there were more than 100 objects detected, and those are assumed to be bones.

"Bones are the most obvious and likely explanation for the radar anomalies," he said. "There's little else it can be."

Up to now, discoveries of multiple bones from a single mammoth have been rare in Alaska.

The best-known mammoth remains might be those from a juvenile that was named Effie. From that single mammoth, head, shoulder and foreleg bones were found in 1948 at a mine on Fairbanks Creek. The University of Alaska's Museum of the North displays a cast of Effie's bones.

Another notable discovery was made in 1983, when remains of two mammoths were found in Western Alaska at Colorado Creek, long a placer mining site.

Most of the mammoth finds in Alaska have been on eroding beaches, along rivers or at placer mine sites -- all "very dynamic" settings, with earth churning significantly over time, Rasic said. "The bones that are found along a river have already moved down that river 10 times," he said. It is, therefore, rare to have bones from a single animal found together, he said.

In contrast, the shallow Bering Land Bridge lake that was the site of this discovery is considered by geologists to be a "low-energy" site, Rasic said. On such shallow lakes, changes occur along the margins and are relatively slow, he said.

In much of Alaska and the far north, accelerated erosion, permafrost thaw and ice melt -- effects of the rapidly changing climate -- have exposed and imperiled ancient artifacts.

In this case, however, the mammoth bones appear to be fairly protected by the cold water, Rasic said. While many shallow tundra lakes are draining and drying out, those changes are not abrupt, meaning there's no need for an emergency excavation, he said.

But it would be worthwhile to keep monitoring the lake and to retrieve the bones if necessary, he said.

Larsen, meanwhile, is now on the lookout for other artifacts as she continues her long-term work surveying conditions of lakes atop changing permafrost in the Arctic and central Alaska.

Woolly mammoths seem well-suited to the open tundra that was once part of a land link to Asia, she said.