USDA National Wildlife Research Center Symposia


Date of this Version

December 1997


Recent survey data have shown the importance of West Sister Island National Wildlife Refuge, Lake Erie, to nesting waders. About 40 percent of all herons and egrets nesting in the U.S. Great Lakes are found there, including the Great Lakes’ largest colonies of great blue heron (Ardea herodias), great egret (Ardea alba), and black-crowned nightheron (Nycticorax nycticorax), and the largest of two snowy egret (Egretta thula). West Sister Island’s importance to Ohio has grown in recent decades with the loss of smaller mainland colonies of waders, especially the black-crowned night-heron. The double-crested cormorant (Phalacrocorax auritus) returned to Ohio as a successful nester in 1992 for the first time in more than a century. The effects of this species on wading bird colonies have been well documented in Canadian Lake Erie. Cormorants have successfully competed against great blue herons for nesting space and eliminated black-crowned night-herons through habitat destruction. Nest estimates made at the island since 1991 indicate that the night-heron has fallen to 37 percent of its historic numbers on the island and is dropping dramatically in the region. That species has been affected negatively as canopy height has increased with vegetative succession. A second concern is the cormorant, whose nest counts have increased from 0 to ~1,500 in 5 years. This rate of increase mirrors that on East Sister Island, a few kilometers northeast in Canada. To date, competition has not been a significant problem, but habitat degradation has been documented, with major leaf loss noted in 1995 on trees having cormorant nests and along the perimeter of West Sister Island. The Ohio Division of Wildlife and the U.S. Fish and Wildlife Service are concerned, both biologically and esthetically, about the future status of the island’s colonies in light of habitat succession and the addition of the cormorant.

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