4.3 Article

AGE-SPECIFIC SURVIVAL OF TUNDRA SWANS ON THE LOWER ALASKA PENINSULA

Journal

CONDOR
Volume 115, Issue 2, Pages 280-289

Publisher

OXFORD UNIV PRESS INC
DOI: 10.1525/cond.2013.110213

Keywords

Alaska Peninsula; apparent survival; Cygnus columbianus; emigration; neck collar; tag loss; Tundra Swan

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Funding

  1. U.S. Fish and Wildlife Service, Izembek National Wildlife Refuge
  2. Institute of Arctic Biology and Department of Biology and Wildlife at the University of Alaska Fairbanks
  3. Alaska Cooperative Fish and Wildlife Research Unit

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The population of Tundra Swans (Cygnus columbianus columbianus) breeding on the lower Alaska Peninsula represents the southern extremity of the species' range is uniquely nonmigratory. We used data on recaptures, resightings, and recoveries of neck-collared Tundra Swans on the lower Alaska Peninsula to estimate collar loss, annual apparent survival, and other demographic parameters for the years 1978-1989. Annual collar loss was greater for adult males fitted with either the thinner collar type (0.34) or the thicker collar type (0.15) than for other age/sex classes (thinner 0 10, thicker: 0.04). The apparent mean probability of survival of adults (0.61) was higher than that of immatures (0.41) and for both age classes varied considerably by year (adult range: 0.44-0.95, immature range: 0.25-0.90). To assess effects of permanent emigration by age and breeding class, we analyzed post hoc the encounter histories of swans known to breed in our study area. The apparent mean survival of known breeders (0.65) was generally higher than that of the entire marked sample but still varied considerably by year (range 0.26-1.00) and indicated that permanent emigration of breeding swans was likely. We suggest that reductions in apparent survival probability were influenced primarily by high and variable rates of permanent emigration and that immigration by swans from elsewhere may be important in sustaining a breeding population at and near Izembek National Wildlife Refuge.

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