When I returned to the Lake Erie shore last year after an absence of several decades, one of the things that surprised me was the explosion in the number of cormorants that had taken place. In fact, I don't recall seeing any when I was a boy. Now they're so plentiful that for the past several years the Ohio Department of Natural Resources (ODNR) and the U.S. Fish & Wildlife Service have been culling their numbers on three Lake Erie Islands. I wanted to find out why.
As it turns out, there was apparently a healthy supply of cormorants - specifically the double crested variety - back in the 1930s and 40s, but gradually, chemical contaminants in the environment caused fatal deformities and reproductive failures and these large, dark, fish-eating waterbirds had all but disappeared from the Great Lakes by mid-century.
But pollution controls led to a remarkable cormorant resurgence. On West Sister Island, Ohio's only chunk of federal protected wilderness, the cormorant population went from zero pairs in 1990 to 3,813 in 2005. Great colonies of great blue herons, black-crowned night herons, and great, snowy, and cattle egrets were threatened by the cormorant invasion. The cormorant's high-nitrogen feces, or guano, burned up vegetation on the island and cormorant numbers as well have crowded out other, less prolific colonials. Cormorants also strip vegetation and break down trees.
On Ohio's tiny, 17-acre Green Island, a state wildlife refuge, cormorant numbers exploded from no pairs in 2003 to 857 by 2005. The ODNR's goal is to eliminate cormorants there entirely. Otherwise, officials fear, the island could be destroyed in another year or two.
Turning Point Island, a long manmade spit of about five acres in Sandusky harbor, had 409 pairs of cormorants a year ago, along with the lake's second-largest colony of black-crowned herons is situated there, along with a fledgling snowy egret colony. Officials want to cull about 40 cormorant nesting pairs there.
Nationwide, cormorant numbers have blossomed to about two million, with nearly 70 percent living in interior areas such as Ohio.
This was the fifth year for cormorant control efforts on West Sister, Green and Turning Point islands. This year nearly 2,200 of the fish-eating birds were killed with noise suppressed rifles in late April and early May before spring foliage took hold. Last year 2,300 cormorants were culled, and in 2008, the number was 2,600.