Cormorant control is showing results
Written by MI Outdoor News   
Friday, 07 January 2005 09:14
There?s more research under way on double-crested cormorants in the Les Cheneaux Islands region of northern Lake Huron ? and, almost certainly, there are fewer cormorants there. Both ends of that equation satisfy Peter Butchko, Michigan director of the U.S. Department of Agriculture?s Wildlife Services program. His office is coordinating both management and research activities. Researchers are studying movement and feeding habits of the birds, which roared back from the vanishing point in the 1970s to Great Lakes populations of more than 1 million. The black, hook-billed, diving fish-eaters have been blamed for sport fish predation, island and shoal habitat destruction, commercial fish farm raids, and competition with other wildlife. Last year, the U.S. Fish and Wildlife Service drafted new rules, which allow Wildlife Services, along with state and tribal officials to take action to reduce cormorant predation. That is a limited authority: citizens cannot harass or kill the birds.) This year, management action took two forms, both aimed at reduced cormorant numbers in the Les Cheneaux Islands region, Butchko told Michigan Outdoor News,
The first, borrowing on a technique used by Canadian officials but really tested here in the states for the first time, was egg-oiling. Breaking cormorant eggs doesn?t accomplish much.The birds simply re-nest. But egg shells are porous, and plugging the tiny holes with oil kills the embryo. Parent birds, none the wiser, continue to incubate in vain until the egg-laying season is over. Egg-oiling proved successful: From 3,220 nests in the Les Cheneaux area, only 41 eggs were known to hatch ? and 31 of them came from nests the technicians didn?t know about. Still, egg-oiling isn?t enough.
"We knew from population models that if you just halt reproduction of cormorants, it?s going to take a long, long time to reduce the population," Butchko said. "They are long-lived birds. In Quebec, they found that you need to combine that with killing or removing a certain number of adult birds." This first year, he said, he arbitrarily set a goal of killing about 15 percent of the adult birds in the Les Cheneaux area. An estimated 6,400 birds nesting there produced a goal of removing 960 birds.
When the shooting stopped, they?d come close, killing 909 birds. But it?s a challenge. "Cormorants are not that stupid," Butchko said. "They don?t just sit there all day and let you shoot at them." As nesting began, officials with noise-suppressed .22-caliber rifles shot many birds on nests. Later, though, it took floating and silhouette decoys to draw the birds into shotgun range. Overall, he said, "We were very, very successful in reducing reproduction, and successful in reducing the population." Butchko said he expects research and management efforts to continue this year, thanks to efforts by U.S. Rep Bart Stupak and Sen. Debbie Stabenow to secure funding for cormorant management ? $125,000 last year and about $150,000 for this year. Also getting accolades was Michigan?s DNR, which he said proved a superb partner, especially in providing fisheries expertise through Dave Fielder at the Alpena research station. Researchers, meanwhile, are using radio transmitters affixed to 72 cormorants to learn more about their behavior and travels. While studies are in their early phase, "It looks like cormorants move around a lot, more than we thought," Butchko said. "And it may get us to the conclusion that if we?re thinking about controlling cormorants in a certain area, we may have to think in larger terms." Other research is taking a close look at what cormorants eat ? a 10-years-later follow-up to studies that indicated cormorants don?t have a huge overall impact on perch populations ? but didn?t focus on certain times of year, such as spawning season, when the effects may in fact be larger.
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