Second North American Sea Duck Conference - Patuxent Wildlife ...

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SECOND NORTH AMERICAN SEA DUCK CONFERENCE Leif Nilsson LONG-TERM TRENDS AND CHANGES IN NUMBERS AND DISTRIBUTION OF WINTERING SEA DUCKS ALONG THE SWEDISH COAST Department of Animal Ecology, Ecology Building, S-223 62 Lund, Sweden; leif.nilsson@zooekol.l u.se Regular counts of wintering waterfowl have been undertaken as a part of the International Waterfowl Census (IWC) and (later) the national Swedish Environmental Monitoring Programme since 1967. After the first years, when one important aim was to study distribution patterns etc, and more or less country-wide surveys were organized, a network of annually surveyed sites was established for the calculation of annual indices. In addition to these about 25 larger sites, a number of smaller counting units were also counted. Country-wide surveys (also including aerial counts) were undertaken 1971- 74, 1987-89, 1992-93 (partial) and 2004, covering all ice-free inshore coastal waters. In this poster I will present the winter distribution patterns and changes in the distribution pattern of sea ducks in Swedish waters in relation to habitat factors also comparing the occurrence of seaducks in brackish Baltic waters in contrast to more marine North Sea water on the west coast. I will also analyze the population development in Swedish sea duck populations during the period 1967-2004. The commonest species of diving ducks in the Swedish inshore waters in January 2004 were Aythya fuligula (220,000), Bucephala clangula (73,000) and Somateria mollissima (49,000). For the commonest species, Clangula hyemalis, only 37,000 were counted in inshore waters, whereas the population wintering on offshore sea shallows in Swedish water is estimated to be at least 1 million individuals. During the survey period marked changes were noted for several of the species studied both as trends in the numbers counted and changes in the distribution. Thus a number of species showed increasing trends over the study period, e.g. Aythya fuligula, Aythya ferina, Bucephala clangula, Somateria mollissima,and Mergus serrator. Some of these trends reflect genuine population changes, whereas other trends are related to changing winter conditions, with a series of milder winters in the latter part of the study period. Some species showed marked changes in the winter distribution during the period, thus Aythya fuligula and Bucephala clangula decreased in the south and increased in the northern part of the coast. 100 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005
SECOND NORTH AMERICAN SEA DUCK CONFERENCE POPULATION TRENDS OF NORTH AMERICAN SEA DUCKS BASED CHRISTMAS BIRD COUNT AND BREEDING BIRD SURVEY DATA Daniel K. Niven¹, John R. Sauer², and Gregory S. Butcher³ ¹National Audubon Society, IL Nat. Hist. Surv., Champaign, IL; dniven@audubon.org ²USGS Patuxent Wildlife Research Center, Laurel, MD ³National Audubon Society, Washington, DC Due to the difficulty of conducting range-wide surveys of either breeding or wintering populations, few data are available to assess the population trends of sea ducks with confidence. We analyze sea duck data from the Audubon Christmas Bird Count (CBC) using hierarchical modeling methods that control for varying effort among circles and over time. These procedures allow us to assess early-winter relative density patterns among states and Bird Conservation Regions (BCRs) while also assessing trends in these regions and across the species North American range. Over the interval 1966–2003, continent-wide declines were observed in 1 of 11 species. Where sufficient data exist, we compare CBC results to estimates of population change derived from the USGS Breeding Bird Survey. The CBC does not effectively sample offshore populations of sea ducks; however, the CBC data can be used to assist in development of species-specific surveys, and CBC data can be used in combination with additional offshore sampling programs to better sample sea duck species. NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA 101
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