Lake Champlain cormorants decline
Candace Page, Burlington Free Press
June 9, 2010
Scientists shared their most recent findings about double-crested cormorants (and the people who hate them) at the Lake Champlain Research Consortium conference Tuesday at the University of Vermont.
To wit:
Cormorants are the big, black, fish-eating birds that have become a common sight on Lake Champlain since a population explosion in the 1990s. Their dense nesting colonies can push out other breeding birds and create a barren landscape of dead trees and guano-streaked ground.
Anglers, in particular, consider cormorants a nuisance species, worrying that the birds will reduce populations of yellow perch and other game fish, although that worry has not been validated by research.
Nevertheless, anglers might be glad to hear a recent study found that cormorants appear to be shifting their diet to another recently arrived nuisance species, the alewife. Alewives arrived in Lake Champlain in 2003 and had spread through the lake by 2007.
Research sponsored by the U.S. Department of Agriculture found that by 2009, alewives made up 70 percent of the diet consumed by cormorants on the Four Brothers Islands. Yellow perch, which composed 78 percent of the birds' diet in 2001-02, made up less than a quarter of what cormorants on the islands ate in 2008 and 2009.
At Young Island in the northern lake, consumption of yellow perch, once 90 percent of the birds' diet, had dropped to 50 percent to 60 percent of their diet by 2008 and 2009.
"Cormorants eat whatever is easiest to catch," said David Capen, a Vermont cormorant researcher not involved in the diet study. They might be able to find alewives in shallow water in great numbers and perhaps sluggish condition in the spring.
Cormorants still eat other lake fish, including rainbow smelt and white perch, the study noted.
Meanwhile, cormorant nests on the Four Brothers declined this year for the first time, to about 3,400 from 4,000 nests in 2009. The Nature Conservancy, which owns the islands, has been applying corn oil to about 2,000 nests each year since 2008 in an attempt to discourage nesting on two of the four islands.
Capen, who studies the Four Brothers population, said the drop in bird nests might reflect a leveling off of cormorants on the lake.
"The population explosion may be over, and the numbers are stabilizing, because that's what populations do," he said. In addition, the states of Vermont and New York, and a federal agency, have been shooting a thousand cormorants a year, he said.
Finally, Walter Kuentzel, a University of Vermont social scientist, and Capen reported the results of their study of human attitudes toward cormorants."
There is public controversy over how to manage cormorants," Kuentzel told the audience. "They are easy to dislike -- they are ugly, messy and smell bad where they nest. On the other hand, there are animal-rights groups who say they are part of nature and deserve protection in their own right."
The researchers questioned 769 anglers, boaters, conservationists and lakeshore homeowners about their knowledge and tested the strength of their attitudes. They asked for reactions to statements such as "Cormorants are like flying rats.
"Their findings: Although some people had strong opinions, most people did not, saying they neither agreed nor disagreed with the test statements. Seventy-five percent of those surveyed agreed cormorants are a nuisance species, for example, but that opinion often was not felt powerfully.
"Overall, the attitude tilts toward the negative side, but not strongly," Kuentzel reported.
Unsurprisingly, he said, anglers had the strongest negative attitude and were most in favor of population control.