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1 December 2012 Survivorship and Mortality Patterns of Double-Crested Cormorants at Spider Island, Wisconsin, 1988–2006
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Banding records were examined to identify changes in mortality causes and locations of Double-crested Cormorants (Phalacrocorax auritus) in Door County, Wisconsin. In 14 out of 18 years between 1988 and 2005, a total of 22,469 birds were banded (300 to 5,462; average 1,605 per active banding year). Of 649 usable band returns (36.1 ± 5.4 per year), 33% were banding-year recoveries (before 1 May of the first year of life). The yearly rate of banding-year recoveries increased from 0.7% per year before 1996 to 2.2% per year after 1999. The yearly proportion of all band recoveries attributed to animal damage control operations also increased over time. The yearly proportion of band returns from Mississippi Delta states increased over time. Mortality rates, both natural and anthropogenic, of cormorants from these colonies appear to have risen as the population has grown and control activities in southern states have increased. Apparent survival rates were estimated by mark-recapture methods during 2001 to 2006. Birds color-banded as adults had a model-averaged annual survival rate of 0.696. For birds banded as nestlings, the model-averaged survival rates were: 0.305 (first year), 0.774 (second and third year), and 0.633 (adults). Simulations of these measured survival rates combined with previously estimated reproductive rates demonstrated that emigration and immigration rates complicate interpretation of these results. Also, simulations demonstrate the potential efficacy of reproductive controls in reducing local breeding populations.

Kenneth L. Stromborg, Jacob S. Ivan, John K. Netto, and Chad R. Courtney "Survivorship and Mortality Patterns of Double-Crested Cormorants at Spider Island, Wisconsin, 1988–2006," Waterbirds 35(sp1), 31-39, (1 December 2012).
Received: 21 September 2007; Accepted: 27 November 2009; Published: 1 December 2012

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