• Abstract and Figures
• Public Full-text

Spring 2005 Scooping for Scoters in Volume 25, Number 1 San Francisco Bay By Susan Wainwright-De La Cruz and boreal forests of Alaska and Canada, and winters John Takekawa along both the Pacific and Atlantic coasts. Surf On a clear, crisp, winter day, a spectacular scoters are long-lived and their lifetime reproduc- array of shorebirds and waterfowl can be easily tion rate is quite low. Juveniles can take two to seen feasting on the mudflats and salt ponds at three years to mature. the Don Edwards San Francisco Bay National Surf scoters have the dubious distinction of Wildlife Refuge, creating a birdwatcherʼs being one of the least studied waterfowl species paradise. When you aim your binoculars beyond in North America. Waterfowl breeding surveys the salt ponds and the mudflats toward the open have been traditionally geared toward dabbling Bay waters, youʼll notice huge rafts of ducks ducks that nest earlier, resulting in a lack of dominating the landscape. Unlike dabbling information for ducks that ducks that feed partially submerged in shallow nest later. Due to this lapse, waters, these bay ducks dive deep to the depths obtaining good estimates of the Bay floor in search of clams and other of surf scoter population invertebrate prey. Peer closely into one of size has proven difficult. In these mixed species groups, and your eyes are addition, the extent of the immediately drawn to white triangular markings surf scoter breeding range on the forehead and neck of a black bird. Its is not well known. Rough bill, bulbous and multi-colored with hues of red, estimates of the North yellow, white, orange, and black, grabs your at- American population size tention next. This male duck standing out from range between 600,000 and the others is just one of 60,000 surf scoters that one million individuals. make the San Francisco Bay estuary their winter However, surveys con- home. ducted since the 1950s show a disturbing trend: Male surf scoter close-up, Surf scoters (Melanitta perspicillata) are scoter populations seem to have decreased by clearly showing distin- sea ducks, waterfowl that molt and winter in about 50%. It is quite difficult to reverse the guishing markings coastal waters.They are one of just three species decline of a species when we know so little about Photo by Dan Gaube, USGS of scoters.White-winged scoters and black its life history. scoters are the other species and are uncommon Biologists across the continent are working in the San Francisco Bay Area. The male surf to improve our knowledge of surf scoters and scoter is quite distinct while females are less to determine the causes of their decline. Current showy with brown bodies, diffuse white patches theories on decline focus on changes that are below their eyes, and bluish-black bills. This occurring throughout the breeding and wintering species breeds in very low densities across the ranges of surf scoters. For instance, global warm- Continued page 2 1 Scooping for Scoters in ing may be reducing the quality of the freshwater ters, and follow them back to their breeding areas boreal lakes scoters use in breeding areas. Also, to examine their reproduction. the majority of wintering surf scoters are found During this study, we discovered that in large, urbanized estuaries where increased capturing surf scoters to attach the radio trans- development, contamination, and invasive spe- mitters was no easy task. They are incredibly cies could be negatively influencing them or their difficult to catch. We first tried to catch scoters primary prey. using mist nets, a net made of fine mesh, early in The San Francisco Bay estuary is one of the morning before the birds could see the nets. the most important wintering areas for surf sco- This method works well in most areas, but not ters along the here - probably because of the ambient lights that Pacific coast. surround the Bay, allowing scoters to see and This estuary, the avoid the nets. We now catch scoters from a boat largest on the with a net launcher that “scoops” them into a net west coast of just off the water. Once caught, we radio-mark North America, birds and track their movements in the Bay seven contains abun- days a week throughout the winter. dant food for We have found that scoters use all bays wintering and in the estuary during early winter, and a large migrating birds. proportion of them are found within the bound- During some aries of the San Pablo Bay National Wildlife years, as much Refuge. By mid-February they begin to congre- as 75% of surf gate in the middle of the San Francisco Bay near scoters counted the San Mateo Bridge, and nearly all scoters are in U.S. Fish found here by the early spring. We were able to Surf scoters in the central and Wildlife Service mid-winter surveys of the determine that most scoters feed in shallow water bay during late winter. lower Pacific Flyway are found right here in our of about six feet, or in the subtidal shoals sur- Photo by Dan Gaube, USGS backyard. Because the Bay is winter home to rounding the edge of the Bay. We also know that such a large fraction of surf scoters, it is crucial they do feed on the Asian clam, as well as a great for us to understand factors here that influence variety of invertebrates, and even fish eggs! this declining species. Scoters on the Pacific coast are associ- Studies conducted in San Francisco Bay ated with spawning of Pacific herring (Clupea in the 1980s have already shown us that pol- pallasi). Herring roe is found in the Bay, often lutants such as mercury, selenium, and cad- in eelgrass beds in the shoals, from November mium accumulate in scoters during the winter. through March, with a peak in January. Concentrations of these contaminants were Unfortunately, herring are at their lowest since higher in scoters than in any other Bay waterfowl the 1970s, and their decline may represent the and were high enough to potentially cause them loss of an important food source for scoters. reproductive problems. Today this threat may be greater because of the invasion of the non-native Very few scoter nests have ever been found Asian clam (Potamocorbula amurensis) in the and their breeding grounds are not well-known. late 1980s. This clam has become widespread in In 2003, we marked females with satellite the northern estuary and has been shown to ac- transmitters and waited for the spring migration cumulate three-times the selenium and 22-times Female surf scoter the cadmium as other clam species. Scoters may foraging on clams in be eating the Asian clam, which could increase San Francisco Bay. their exposure to these pollutants. Photo by Dan Gaube, USGS In 2003, we began a study of San Francisco Bay surf scoters to determine what they are eating and how much they are being affected by pollution. We are also attempting to track their migration routes with radio transmit- 2 3 San Francisco Bay to begin. Using satellite receivers, we followed these birds northward along the west coast and to their breeding area in the Northwest Territories of Canada between the Great Slave and Great Bear Lakes, a distance ranging between 2000 and 2500 miles. For a detailed map, log on to http://www.werc.usgs.gov/scoter. Once we discovered how and where these birds go, we went to the breeding area to find the nests and to determine the types of nesting habitat that scoters favor. Flying in floatplanes, our crew was able to observe three different radio-marked scoters on small lakes scattered across this very large region. Our future work on the breeding ground will include determining whether pollutants affect scoter reproduction. Over the next three years, weʼll continue scooping for scoters to learn more about their wintering activities in the San Francisco Bay, ogy and cross-seasonal contaminant effects in Migration routes of surf Pacific Flyway, and in the breeding grounds. surf scoters. scoters. This information will help in their recovery, and, John Takekawa is a research wildlife Courtesy of USGS with any luck, you will see more of their colorful biologist with the U.S. Geological Survey, San bills in our Bay Area waters. Francisco Bay Estuary Field Station which is co- Susan Wainwright-De La Cruz is a wildlife located with the San Pablo Bay National Wildlife biologist with the U.S. Geological Survey, San Refuge on Mare Island in Vallejo. His research Francisco Bay Estuary Field Station and a specialities include migration and wintering graduate student at the University of California, ecology of waterbirds, radio telemetry, salt pond Davis. Her research focuses on foraging ecol- ecology, and wetland restoration. TIDELINE Don Edwards Warm Springs San Francisco Bay Wildlife Society Published quarterly by Don Edwards San Francisco Unit Manager: .................................... Sally Reynolds A nonprofit 501(c)(3) cooperating association es- Bay National Wildlife Refuge, with funding from San Don Edwards Refuge Operations Specialist:.............. tablished in 1987 to promote public awareness and Francisco Bay Wildlife Society. Eric Mruz appreciation of San Francisco Bay and fund educa- Volume 25, Number 1 Farallon Refuge Manager:....................... Joelle Buffa tion and outreach programs at San Francisco Bay Editor: ................................................ Carmen Minch Farallon Refuge Operations Specialist: ....Jesse Irwin National Wildlife Refuge Complex. San Pablo Bay Manager:......................Christy Smith To receive Tideline, email carmen_leong-minch@ Board of Directors fws.gov, or write to: Tideline, Don Edwards San South Bay Refuges Manager: ...............Ivette Loredo Antioch Dunes Refuge Manager: ............Chris Bandy President: ....................................Christopher Kitting Francisco Bay National Wildlife Refuge, P.O.

Load more

  16

Copy Link