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Mortality of Colonial Waterbirds in Eastern Lake Ontario Associated with Type E Botulism.
SHUTT, J.L.1, WESELOH, D.V.2, PEKARIK, C.3, and WILLIAMS, K.L.2
11Environment Canada, National Wildlife Research Centre, Ottawa, ON, KIA 0H3
2Canadian Wildlife Service, Downsview, ON, M3H 5T4
3Canadian Wildlife Service, Burlington, ON, L7R 4A6
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Abstract
Type E botulism was first recorded in birds in the Great Lakes in the early 1960s (Herman 1964) and was not documented in colonial waterbirds in Lake Ontario until 2002. Since then, epizootics of type E botulism involving gull species and double-crested cormorants (DCCOs) in Lake Ontario have occurred annually. Following a significant die-off during the summer of 2004, we initiated regular surveys of colonial waterbird breeding sites during the summer and fall of 2005 to document mortality in fish-eating birds associated with type E botulism. Numbers of dead birds recovered were related to trends in local population size. Between the 8th of July and the 14th of November 2005, 2087 dead or moribund birds were counted on 6 islands in eastern Lake Ontario. The total consisted of 1429 (68% of total) DCCOs, 300 (14%) ring-billed gulls, 192 (9%) herring gulls, 73 (4%) great black-backed gulls (GBBGs) and 68 Caspian terns (3%). The remainder (1%) consisted of shorebird and duck species (22 individuals). Since 2002, populations of herring and great black-backed gulls in the eastern basin of Lake Ontario have declined (breeding GBBGs declined by 75%). The recent occurrence of type E botulism in Lake Ontario may be related to the introduction of exotic species and changes in water clarity.
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