Response of double-crested cormorants to a large-scale egg oiling experiment on Lake Huron

Authors

  • Mark S. Ridgway,

    Corresponding author
    1. Harkness Laboratory of Fisheries Research, Aquatic Research Section, Ontario Ministry of Natural Resources, Trent University, 2140 East Bank Drive, Peterborough, ON, Canada K9J 7B8
    • Harkness Laboratory of Fisheries Research, Aquatic Research Section, Ontario Ministry of Natural Resources, Trent University, 2140 East Bank Drive, Peterborough, ON, Canada K9J 7B8
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  • Trevor A. Middel,

    1. Harkness Laboratory of Fisheries Research, Aquatic Research Section, Ontario Ministry of Natural Resources, Trent University, 2140 East Bank Drive, Peterborough, ON, Canada K9J 7B8
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  • J. Bruce Pollard

    1. Wildlife Section, Ontario Ministry of Natural Resources, 300 Water St., Peterborough, ON, Canada K9J 8M5
    Current affiliation:
    1. Canadian Wildlife Service, Environment Canada, 17 Waterfowl Rd., Sackville, NB, Canada E4L 1G6.
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  • Associate Editor: Graham Hall

Abstract

We report on a management experiment examining the effects of large-scale egg oiling on double-crested cormorant nest abundance and measures of seasonal cormorant density (bird-days/km2) from 2000 to 2005. We employed the staircase design to distinguish transient responses to management treatments from site and year effects that generally contribute to variation in populations. The response to egg oiling in Georgian Bay was as expected with a decline in nest abundance attributable to egg oiling. In the North Channel, nest abundance did not decline because of egg oiling but increased, reflecting either retention of nesting adults or recruitment to colonies. This surprising outcome may stem from fish escapement from pen rearing facilities in the vicinity of the oiling experiment in the North Channel. We observed no effect of egg oiling on the July–August seasonal density of cormorants. The strongest effect size was associated with site effects followed by year effects for nest abundance and seasonal density. The effect size of egg oiling on variation in nest abundance did not exceed 5% for any year in both the North Channel and Georgian Bay. Fish pen culture appears to affect coastal distribution of cormorants. © 2011 The Wildlife Society.

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