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Teamwork Sheds Light on Shorebird-Migration Mysteries
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Ready for tracking: A radio-marked dunlin. Photograph by USGS.
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Following the spring migration of shorebirds along the Pacific coast is a daunting task. Migratory birds travel thousands of miles from their wintering areas in southern latitudes to their Arctic breeding areas. Most shorebirds stop to "fuel up" from a few days to a few weeks at key wetland sites. Recognizing and conserving key migration areas is crucial for protecting these long-distance travelers, yet few studies have examined the complete migration path of a shorebird species because of the difficulty of working across such vast areas. Over the past decade, I have worked with scientists at the Prince William Sound Science Center (a nonprofit research organization in southeastern Prince William Sound, Alaska) and Point Reyes Bird Observatory (a nonprofit research organization northwest of San Francisco, CA) to tackle this problem.
Although radio transmitters have been developed recently that enable biologists to track ducks and larger birds with satellites, most shorebirds are too small for this technology. Instead, we enlisted the help of a team of biologists at migration areas from California to Alaska to listen for shorebirds marked with miniature, 1-gram transmitters. We used mist nets and rocket nets to catch three species of shorebirds at San Francisco Bay and Grays Harbor, WA, in early April 2001. The transmitters were glued on the backs of dunlin, short-billed dowitchers, and long-billed dowitchers. The transmitters were designed to work for about 6 weeks and then fall off the birds.
Dowitchers: Three long-billed dowitchers captured and radio-marked for migration studies. Photograph by USGS.
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Biologists worked in aircraft and on the ground to track 82 birds during April and May from San Francisco Bay northward. We located 88 percent of the individuals with working transmitters north of the area where they had been marked. The most important migration area was the Copper River Delta in Alaska, where we heard 76 percent of the radio-marked birds: 79 percent of the dunlin, 63 percent of the short-billed dowitchers, and 76 percent of the long-billed dowitchers. The second most important region was Grays Harbor and Willapa Bay in Washington.
The length-of-stay varied by species in the areas where the birds were captured. In San Francisco Bay, long-billed dowitchers stayed an average of 7.7 days, whereas short-billed dowitchers stayed an average of 10.8 days before migrating. We estimated the duration of a shorebird's stay at a particular migration area to range from 1 to 5 days. Such rapid turnover suggests that daily to weekly counts may represent different individuals and that some areas may support much larger numbers of birds than previously estimated.
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Examination: Each bird is measured and weighed to examine its condition before marking. Photograph by USGS.
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Shorebirds may follow different strategies at different migration sites. For example, only a small proportion of long-billed dowitchers were detected at Grays Harbor, suggesting that they either used other wetlands or flew longer distances than the other species. Birds generally stayed longer at Willapa Bay, a "staging" area where birds stopped for longer periods to accumulate fuel. Individuals that arrived later tended to stay for shorter periods, suggesting that they may have only a limited period to begin breeding.
Our project was recently recognized by the U.S. Forest Service with a Taking Wing Award for contributions to migratory-bird conservation. Work continues in 2002 with the first effort to follow the spring migration of radio-marked shorebirds from northern Mexico. With cooperators from local universities in Sinaloa, we will radio-mark western sandpipers and dowitchers with added listening posts in San Diego Bay, the Salton Sea, and Point Mugu in southern California and Stillwater National Wildlife Refuge in Nevada. Our project will be featured on the Sister Shorebirds Schools Web site and list server, an environmental-education program sponsored by the U.S. Fish and Wildlife Service. This Web page received more than 125,000 hits last year, including subscribers from 36 States and 23 different countries.
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May 2002
in this issue:
cover story:
Contaminants Sampling Cruise - San Francisco
Ground-Truthing Coral Reef Maps
Shorebird Migration
CO2 in Saline Aquifers
Early Earth Day in Florida
Honduras Coral Reef Documentary Online
Girl Scouts
University Job Fair
Sea-Level Rise Lecture
Massachusetts Sea-level Rise Briefing
New Directions Workshop
Floating Support Facility
Howell New Patuxent Director
WHFC Runners
Water-Column Optics Talks
Special Emphasis Program
New Employees
Mendenhall Fellow Presents Talk
May Publications List
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U. S. Department of the Interior | U.S. Geological Survey
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