UNIQUE ISLAND HABITATS MAY BE THREATENED BY DOUBLE-CRESTED CORMORANTS |
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Authors: | CRAIG E HEBERT JASON DUFFE D V CHIP WESELOH E M TED SENESE G DOUGLAS HAFFNER |
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Institution: | 1. Canadian Wildlife Service, National Wildlife Research Centre, Carleton University, Raven Road, Ottawa, Ontario, K1A 0H3, Canada;2. Canadian Wildlife Service, Ontario Region, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4, Canada;3. Ontario Ministry of Natural Resources, RR1 Airport Road, Gravenhurst, Ontario, P1P 1R1, Canada;4. Department of Biology, University of Windsor, Windsor, Ontario, N9B 3P4, Canada |
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Abstract: | Abstract: Double-crested cormorant (Phalacrocorax auritus) populations on the Great Lakes expanded greatly during the past 2 decades. On Lake Erie, the number of breeding cormorants increased from 174 birds (87 nests) in 1979 to 26,542 (13,271 nests) in 2000. In 2000, 81% of the breeding population was on 2 western-basin islands (East Sister and Middle Islands). The plant communities on these islands represent some of the last remnants of Carolinian vegetation in Canada. Our study is the first to quantitatively assess the relationship between the distribution of nesting cormorants and forest health. On East Sister Island, 2 measures of forest cover were obtained using infrared aerial photographs and ground-based measurements of leaf area index. These measures of forest cover were correlated (rs = 0.70, P < 0.001), which validated the use of remotely sensed data to assess forest cover. Cormorant nest density was negatively correlated with tree cover on both East Sister and Middle Islands. Temporal comparisons of Middle Island data indicated a reduction in tree cover from 1995 to 2001, and these reductions coincided with a large increase in the island's cormorant population. Although correlational in nature, our results suggest that cormorants may be detrimentally affecting island forests. |
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Keywords: | cormorant populations double-crested cormorant forest cover Great Lakes habitat destruction Lake Erie leaf area index Phalacrocorax auritus |
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