Alaska trumpeter swans filling historic range
A 1968 Alaska census found just 2,847 trumpeter swans. Random sampling in 2010 estimated 25,347 - a nearly nine-fold increase.
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ANCHORAGE, Alaska -- It was likely easier than ever to see a migrating trumpeter swan this year,
as the big white birds continued a remarkable comeback from near extinction in the Lower 48 states
and much of their Alaska habitat, a federal wildlife biologist said.
"They still have not recovered to their full range that they once occupied prior to the 1880s, but they've done fantastically in Alaska," said Deborah Groves, who has counted Alaska swans since 1990.
A 1968 Alaska census found just 2,847 of the birds. Random sampling in 2010 estimated 25,347 - a nearly nine-fold increase.
Trumpeters are known for their distinctive call that the Cornell Lab of Ornithology calls "hollow, nasal honking." The Alaska Department of Fish and Game says it's deep, like a French horn.
With 7-foot wingspans, trumpeters are North America's largest waterfowl. Males average 28 pounds, females 22 pounds, and eggs are up to 5 inches long, the department says.
The birds were hunted throughout the 1800s for meat and feathers, which made fine quill pens. By the early 1930s, Groves said, there were only 69 known trumpeters in Yellowstone National Park.
Hunting ended and biologists made a happy discovery when they began bird work in Alaska: A remnant population of a couple of thousand trumpeters remained, Groves said.
Alaska biologists did their first formal trumpeter survey in 1968, another in 1975 and every five years since then.
"They were increasing almost exponentially for a while," Groves said.
Biologists in 2005 detected a continued boom, even though they suspected the habitat of the birds was saturated. By 2010, the count switched to sampling rather than a census because of the trumpeters' wide range.
"It's nice to have that problem," Groves said.
The population may finally be leveling off. Biologists detected a 7 percent increase between 2005 and 2010. Growth slowed in the Copper River Basin near Glennallen but remained high in areas such as the vast Yukon Flats, the wetlands where the mighty Yukon River changes direction from northwest to southwest.
Eventually, Groves said, the expanding swan population will expand to less bountiful wetlands.
Severe weather is a factor that limits population growth among young birds.
"It takes almost 150 days or more to go from nest-building, laying eggs, incubating, rearing the young, to the point where the young can fledge," she said. "In Alaska, they're butting right up against breakup and freeze-up with that time period."
She's not sure what effect global warming might have had on the population growth or the range of the birds.
"It probably has had some effect and it certainly could have an influence in the future," she said.
The population has been limited by a loss of winter habitat in estuaries of the Pacific Northwest. At the same time, she said, swans have learned to take advantage of farm fields.
"That's an issue now," she said.
Trumpeters technically are game birds, but Groves has not heard suggestions for a resumption of hunting.