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In a pioneering study, a team led by the U.S. Geological Survey (USGS) has tracked a surf scoter from its coastal wintering grounds in San Francisco Bay to its nest 2,000 mi away in the vast northern boreal forest of interior Canada. By marking individual surf scoters with satellite and radio transmitters while these sea ducks wintered in San Francisco Bay, the team was able to document the birds' spring migration from wintering grounds to breeding grounds.
"In migratory-bird studies, cross-seasonal research linking wintering and breeding areas is something of a Holy Grail," said John Takekawa, wildlife biologist and principal investigator with the USGS Western Ecological Research Center's San Francisco Bay Estuary Field Station in Vallejo, CA. "Many of these migratory species nest thousands of miles from where they spend the winter, and it is difficult to determine which group is from where."
Making such linkages may be vital to understanding alarming declines in sea duck numbers during the past few decades. Many sea ducks breed in northern boreal-forest and tundra areas and winter in marine environments. Degradation of their remote northern breeding habitats, possibly linked to global climate change, has been suggested by some researchers as a possible explanation for the decline in these species. At the same time, these ducks may be threatened by human activities in their major coastal wintering areas. The San Francisco Bay region supports the largest wintering population of surf scoters in the Pacific Flyway; however, it is also home to 8 million people, who outnumber surf scoters by 250 to 1.
Habitats in San Francisco Bay are impaired by pollutants, including mercury. Historically, mercury deposits were mined in the Coast Ranges and used for extraction of gold by placer miners in the Sierra Nevada during the Gold Rush era that began in 1849. Mercury accumulated in sediment that was eroded in the mining process and has since flowed downstream to be deposited in the bay. Surf scoters found in San Francisco Bay have elevated mercury levels, but little is known about the effects of this contaminant on their breeding success.
"Although surf scoters breed from Quebec to Alaska, our preliminary studies in 2003 showed that most birds marked with satellite transmitters in San Francisco Bay were distributed in a band a few hundred miles wide at the edge of the treeline from Great Slave Lake to Great Bear Lake in [Canada's] Northwest Territories," said USGS biologist Susan De La Cruz.
Last winter, partnered with the U.S. Fish and Wildlife Service (USFWS) and supported by the Calfed Ecosystem Restoration Program, De La Cruz led the capture and radio marking of 90 surf scoters to follow them to their nests. In mid-June 2005, the project came to fruition as Matt Wilson, a USGS biologist and graduate student at the University of California, Davis; Rod King, a USFWS pilot-biologist; and USGS intern Kenny Farke tracked a satellite-marked bird to a lake 80 mi east of Yellowknife, Northwest Territories. After landing in a floatplane, they searched along the lakeshore until finally spotting the satellite-marked hen sitting on six eggs in a downy nest.
"The eggs were freshly laid within a day or two," reported Wilson, who used a tube to "candle" or determine the age of the incubating eggs. Samples from this nest and others like it will be tested to determine whether contaminants from urbanized southern wintering regions may be affecting the reproduction of migratory birds breeding in the north.
Along with this first step in documenting breeding effects, the team is working with biologists from the Washington Department of Fish and Wildlife, the Canadian Wildlife Service, Simon Fraser University, and the USGS Alaska Science Center, with support from the North American Sea Duck Joint Venture, to examine the breeding distribution of surf scoters from major Pacific coast wintering areas that extend from Mexico to British Columbia. With such cross-seasonal information, it may be possible to determine more reliably which wintering populations are vulnerable to emerging threats in the breeding areas, such as a proposed natural-gas pipeline along the Mackenzie River and development of extensive beds of oil sands in northern Alberta.
To learn more about this USGS surf scoter study, please visit Migration of Surf Scoters Along the Pacific Coast.
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