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

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SECOND NORTH AMERICAN SEA DUCK CONFERENCE ESTIMATING POPULATION ABUNDANCE AND MAPPING DISTRIBUTION OF WINTERING SEA DUCKS IN COASTAL WATERS OF THE MID-ATLANTIC Mark D. Koneff 1 , J. Andrew Royle², Douglas J. Forsell³, James S. Wortham¹, G. Scott Boomer¹, and Matthew C. Perry² ¹USFWS, Division of Migratory Bird Management, Laurel, MD; Mark_Koneff @fws.gov ²USGS, Patuxent Wildlife Research Center Laurel, MD ³FWS, Annapolis, MD, USA. Survey design for wintering scoters (Melanitta sp.) and other sea ducks that occur in offshore waters is challenging because these species have large ranges, are subject to distributional shifts among years and within a season, and can occur in aggregations. Interest in winter sea duck population abundance surveys has grown in recent years. This interest stems from concern over the population status of some sea ducks, limitations of extant breeding waterfowl survey programs in North America and logistical challenges and costs of conducting surveys in northern breeding regions, high winter area philopatry in some species and potential conservation implications, and increasing concern over offshore development and other threats to sea duck wintering habitats. The efficiency and practicality of statistically-rigorous monitoring strategies for mobile, aggregated wintering sea duck populations have not been sufficiently investigated. This study evaluated a 2-phase adaptive stratified strip transect sampling plan to estimate wintering population size of scoters, long-tailed ducks (Clangua hyemalis), and other sea ducks and provide information on distribution. The sampling plan results in an optimal allocation of a fixed sampling effort among offshore strata in the U.S. mid-Atlantic coast region. Phase 1 transect selection probabilities were based on historic distribution and abundance data, while Phase 2 selection probabilities were based on observations made during Phase 1 flights. Distance sampling methods were used to estimate detection rates. Environmental variables thought to affect detection rates were recorded during the survey and post-stratification and covariate modeling were investigated to reduce the effect of heterogeneity on detection estimation. We assessed cost-precision tradeoffs under a number of fixed-cost sampling scenarios using Monte Carlo simulation. We discuss advantages and limitations of this sampling design for estimating wintering sea duck abundance and mapping distribution and suggest improvements for future surveys. 22 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005
SECOND NORTH AMERICAN SEA DUCK CONFERENCE APPARENT ANNUAL SURVIVAL AND NEST SUCCESS OF PACIFIC COMMON EIDERS IN CENTRAL ARCTIC CANADA Andrea K. Hoover, D. Lynne Dickson, and Kevin W. Dufour Canadian Wildlife Service, Environment Canada; andrea.hoover@ec.gc.ca Between 1976 and 1996, North American population indices of Pacific common eiders (Somateria mollissima v-nigra) declined by more than 50% based on spring migration counts at Point Barrow, AK. Although the population trend is based on infrequent surveys (4 spring migration counts over 20 years), there is general agreement of concern for the status of Pacific common eider populations. Reasons for the decline are unknown, but are either a function of decreased annual survival, decreased recruitment, or both. In 2001, we initiated a study to estimate annual survival for breeding females, and nest success over a five year period in a core breeding area for Pacific common eiders in the central Canadian arctic. In addition, we monitored nest initiation dates, nest site selection, predation, and influences of sea ice to evaluate their effects on nest success and ultimately recruitment. Eiders were captured and marked prior to nesting between 15 - 30 June and resighted during 19 June - 30 July in years 2001-2004. Although results should be considered preliminary and interpreted with caution at this time, capture-recapture analysis based on open population models indicated a marked decline in apparent annual survival of breeding females over the available 4 years of study (2001: 0.74 ± 0.07 SE; 2002: 0.66 ± 0.06; 2003: 0.57 ± 0.07; n = 190). We conducted nest searches between 28 June and 18 August on islands in marine and freshwater environments and calculated a Mayfield nest success estimate. Nest success for all 4 years combined was consistently greater on freshwater islands (0.57 ± 0.001, n = 951) than on marine islands (0.26 ± 0.002, n = 1409), although nesting on marine islands is more typical throughout the Pacific common eider’s range. Median nest initiation dates were similar among years, and were approximately 1-2 weeks earlier at the freshwater islands (27 June) than at the marine islands (6 July). The overwhelming cause of nest failure was predation, and observations suggested that mammalian predation caused greater complete nest loss on an island than avian predation. Results from our study provide valuable information to evaluate changes in population trends, however further research is necessary to determine the relative contribution of each of these population parameters to Pacific common eider population dynamics. NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA 23
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