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Title: Movement, Survival Rate Estimation, and Population Modelling of Eastern Tundra Swans, Cygnus columbianus columbianus
Authors: Wilkins, Khristi
Keywords: tundra swan
population model
survival rate
bird conservation region
habitat use
eastern population
Issue Date: 12-Dec-2006
Abstract: The Eastern Population (EP) of tundra swans (Cygnus columbianus columbianus) winters in the eastern United States and breeds from the North Slope of Alaska to the eastern side of Hudson Bay in Canada. EP swans were marked on the wintering grounds in Maryland, North Carolina, Pennsylvania, and Virginia in order to study movements, habitat use, survival, and population structure. Swans were marked with individually coded neck collars (n=1,471), USFWS leg-bands (n=3,504), and satellite-tracked radio transmitters (n=43) from February 1997?March 2002. Location information was collected from February 1997?March 2003 via ground observers, recapture, recovery of dead birds, or satellite location. Satellite-tracked EP tundra swans spent approximately 7 months each year on breeding or wintering grounds, and about 5 months of each year in migration. Significant time spent in migration highlights the importance of migratory habitats to this population. No sub-populations were identifiable based on the exclusive use of migratory pathways, Bird Conservation Regions, wintering grounds, or breeding grounds. Movement rates between states on the wintering grounds (Maryland, North Carolina, Pennsylvania, and Virginia) ranged from 0.00 to 0.46, but were rarely different from 0.25 (P<0.05), which suggested that exchange between states caused significant mixing of the population within and between years. Indirect survival rates of marked adult swans ranged 66?84% depending on analytical method or marker type, but were statistically similar (95% confidence intervals overlapped). Use of neck collars in operational marking program is not recommended for future studies due to the cost and difficulty of collecting representative data. To investigate the necessity of annual survival rate estimates, I used data from operational monitoring programs (Mid-Winter Index [MWI], winter ground Production Survey, number of hunting permits, retrieved swan harvest) to develop a model of EP tundra swan dynamics. The model provided reasonable and precise predictions of population size, harvest, and survival. The model can help to predict and understand the effects of harvest on population size. Analyses did not detect density-dependence in recruitment and suggested that a population size goal of at least 80,000 swans can be sustained at current or slightly decreased levels of harvest.
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