For years, Quartermaster Harbor has provided a winter refuge to the western grebe, an elegant, long-necked diver that has experienced a precipitous decline throughout Puget Sound.

So important were its numbers off the shores of Vashon and Maury that in 2001 the National Audubon Society and the Washington Department of Fish and Wildlife declared Quartermaster Harbor an “Important Bird Area.” Its presence here has been a kind of badge of honor for the Island: The Vashon Audubon made the western grebe its logo, a bird that graces all of its literature.

Now, however, the iconic seabird seems to be vanishing from Quartermaster as well.

During the Christmas Bird Count last month, Islanders counted 17 western grebes — a decline from 366 last year and an enormous drop from the 1,500 to 2,000 western grebes birders counted in Quartermaster Harbor in previous years.

The decline has sobered birders, some of whom have spent years tallying their numbers.

“Quartermaster Harbor was one of the last remaining places where the western grebe had not decreased,” said Islander Dan Willsie, who counted the grebes for the Dec. 28 Christmas Bird Count on Vashon. “And now our population has just plummeted. It’s a complete free fall.”

Vashon naturalist Ed Swan said birders who gathered for a potluck following the count were struck by the magnitude of the grebe’s decline.

“Just like the orcas, it’s another huge red flag that says we need to do something for Puget Sound,” he said.”It’s another big sign that our marine waters need a lot more attention.”

The western grebe is the largest of the four grebe species that inhabit the waters off of Vashon; the other three are the rednecked, horned and eared grebe.

All are declining, as are other diving birds, including the region’s three different species of loons. None, however, are experiencing the dramatic drop in numbers that birders are seeing with the western grebe, and as a result, the western grebe’s decline is capturing the attention of researchers throughout the region.

All told, biologists believe the western grebe’s numbers have fallen by 80 to 85 percent — from a high of 100,000 in the 1970s to around 15,000 now, said David Nysewander, a research biologist with the state Department of Fish and Wildlife.

Nysewander, who has been studying the western grebe for more than a decade, said he doesn’t believe the grebes are simply moving from one part of Puget Sound to another. The birds, which winter in the region, have what he called “high site loyalty,” a strong attraction to the same place year after year.

It’s possible they’re moving much farther south, to California, but he and other researchers can’t know for sure, he said. Recent efforts to monitor the birds didn’t work; scientists captured 10 of the birds and implanted transmitters into them — all of whom presumably died from the trauma of the implant procedure or some other related issue, he said.

Nysewander speculates that the birds are in decline for several reasons. They’re diving birds that depend on small fish — and in particular herring — for their diet, and some believe herring numbers are down, he said.

The bird is also more vulnerable than most to oil spills; unlike other water birds, western grebes don’t leave the water — and thus they get soiled badly by oil or other contaminants in the water. Gill nets — particularly the discarded “ghost nets” scattered on the Sound’s floor — are also known to injure and kill grebes.

Problems also plague the grebe on its nesting grounds, found in freshwater lakes and ponds north, east and south of the Sound, Nysewander said.

The grebes build their nests in the water, which are held in place by underwater vegetation. As a result, boating, waterskiing and other activity can disrupt them, he said. Their nests are also affected by irrigation and other practices that lower the water level.

But because of their dependence on forage fish, Nysewander says they’re a top-of-the-food-chain animal in Puget Sound’s marine ecosystem — and thus their decline is like the proverbial canary in the coal mine, he said, a reflection of the overall decline of the Sound’s health.

“It really concerns me,” he said of the western grebe’s falling numbers. “I feel the declines are real and mourn the loss myself.”

Willsie, who counted the western grebes during last month’s bird count, is also saddened by the bird’s decline. More than anyone on Vashon, Willsie has come to represent the grebe’s leading advocate on the Island.

A retired Boeing manager, he has spent countless hours tallying the birds over the past 25 years, including one stretch where he drove around the entire Puget Sound region, counting western grebes from the shore using a high-powered spotting scope.

Indeed, it was Willsie’s research that first identified Quartermaster Harbor as one of their last best sanctuaries in the region, resulting in Audubon and the state naming the inland bay an Important Bird Area.

It was an auspicious moment for those who care about birds. Newspapers throughout the region noted Quartermaster’s special status, including a story in the Feb. 26, 2001, edition of the Seattle Times headlined, “Wintering grebes grace Vashon.”

A Vashon native, Willsie said he began birding at age 10, when a neighbor’s observations of the returning violet-green swallows captured his attention. Now, he added, he’s both troubled and puzzled by the grebe’s decline.

“I wish I had about five young Ph.D candidates down here working on Quartermaster Harbor,” he said. “I’m just incredibly curious to know what’s happening.”

Last week, Willsie stood next to one of the five signs along the shores of Quartermaster that notes its designation as an Important Bird Area. He spotted a lone horned grebe, making delicate, s-curve dives into the dark water just off the shore. Not a single western grebe could be seen.

Quartermaster remains an important bay for seabirds, especially those species — such as scoters and goldeneyes — that eat crustaceans, he said; hundreds of scoters were identified during last month’s count. But he’s dismayed by the dearth of grebes.

“Western grebes are very graceful; they’re just beautiful birds,” he said.