Double-crested Cormorant
The Double-crested Cormorant was at one time an endangered species in North America, primarily because of DDT contamination. It has made dramatic recoveries and is common on the Great Lakes. Its recovery has brought about calls for reduction in its numbers. Culls have taken place in both Canada and the United States. Much of the impetus for these culls seems to have been created by sports fishing organizations.
Point Pelee National Park are planning to kill thousands of birds on Middle Island starting this week.
One of the main issues is the claim that Cormorants are a threat to the Yellow Perch population. A study commissioned by the U.S. Fish and Wildlife Service (and later ignored by them), found that Cormorants took about 1% of the legal size Yellow Perch and Sports fishing took about 2.5%, but that neither had an impact on the population.
Cormorants have been blamed for declines in the populations of other colonial nesting species like Black-crowned Night Heron, although I have found no studies that show this. In Hamilton bay, Ontario, I have seen a colony of Night Herons , who had shared nesting trees with cormorants, desert it as the trees dies and became bare. However, they merely relocated to a more favorable tree nearby.
The question of vegetation impact has also been put forth as a good reason for reducing the species’ numbers, and there is no doubt that the acidity of their guano kills off plants. Whether this is sufficent reason is questionable, and seems especially dubious considering the massive habitat loss caused by human populations.
Arguments against culling include the fact that it is not done in a humane manner, with many birds left injured who eventually starve. Proponents suggest oiling of eggs as a solution.
The process of culling is also a disturbance to other colonial breeders and probably does far more damage to them than the cormorants presence.
Double-crested Cormorant
Diana, J.S., S. Maruca, and Bobbi Low. 2006. “Do increasing cormorant populations threaten sportfishes in the great lakes? A case study in Lake Huron.” Journal of Great Lakes Research, 32 (2): 306-320 (Abstract)
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