Loons on the edge

摘要

Most mercury gets into lakes from atmospheric deposits. Coal-burning, incineration, and other industrial processes pollute the air. Pollutants can travel for hundreds of miles, falling on lakes where loons breed. When the mercury falls into the water, bacteria convert it to an organic form called methylmercury that infiltrates the bottom of the food chain, gets ingested by fish, and then is consumed by loons that eat the fish. Each time the methylmercury passes to a higher predator, the amount in the organism increases. Research has shown that mercury levels in Minnesota and Wisconsin have increased by 400 percent during the past 150 years. Loons don't normally die directly from mercury poisoning. But high levels of mercury in their systems can make them more susceptible to disease and slow their response rates to external stimuli such as an approaching predator. One male with above-normal mercury levels captured in Michigan would not incubate the eggs laid by its mate. Normally males share equally in that responsibility or at least help when the female leaves the nest to feed. The nest failed. The male was found later that summer, dead.