Annual and seasonal survival of trumpeter swans in the upper midwest

Authors

  • Dana M. Varner,

    Corresponding author
    1. Cooperative Wildlife Research Laboratory, Southern Illinois University, Carbondale, IL 62901, USA
    Current affiliation:
    1. School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL 36832, USA.
    • Cooperative Wildlife Research Laboratory, Southern Illinois University, Carbondale, IL 62901, USA.
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  • Michael W. Eichholz

    1. Cooperative Wildlife Research Laboratory, Southern Illinois University, Carbondale, IL 62901, USA
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  • Associate Editor: Bret Collier.

Abstract

The reintroduction of trumpeter swans to the north central United States appears to be a conservation success story. For the most part, population management goals have been met or exceeded. The population cannot be considered self-sustaining, however, because 90% of the swans migrate short distances to wintering sites where supplemental feeding occurs. The remaining 10% migrate longer distances to areas where adequate open water and forage occur naturally. To determine how these 2 different wintering habits might affect mortality, we used mark-resight data gathered between 2000 and 2008 to estimate and compare annual survival rates for long- and short-distance migrant swans marked in Wisconsin. Apparent annual survival rates were similar for long- (0.81, SE = 0.019) and short- (0.81, SE = 0.022) distant adult migrants but were higher for long-distance sub-adult (0.86, SE = 0.036) migrants than for short-distance sub-adult migrants (0.7, SE = 0.046). We also estimated seasonal survival of long-distance migrants to determine if the migratory periods are a time of high mortality. We found little evidence for seasonal variation in survival and estimates for both migratory and non-migratory seasons were very high (>0.97). Overall, the results suggest that little mortality occurs during migration and long-distance migrants are able to survive at rates at least equal to, but probably higher than, short-distance migrants. © 2011 The Wildlife Society.

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