National Geographic : 2009 Nov
PHOTOS: ARTHUR MORRIS, CORBIS ABOVE ; DANIEL POLESCHOOK, JR., AND GINGER GUMM TOP ENVIRONMENT Mercurial Loons Why are some loons acting so, well, loony? Mercury. Long-term studies of common loons in the United States and Canada reveal that the toxic stuff is invading birds' brains and bodies in dangerous concentrations. It's disrupting behavior and physiology---and could put loon populations in peril. Mercury is a naturally occurring metal, but industrial activities like coal burning emit more than double nature's share. In water- ways mercury can turn into the even more insidious methylmercury and infiltrate the food chain, its potency building at each level. Loons, which eat contaminated fish, are among the harder hit species. Conservation biologist David Evers and colleagues report that loons with high methylmercury levels lay smaller eggs (left), forage less often, and spend less time nesting--- leading to 41 percent fewer fledged chicks. Another study shows highly toxic loons produce no chicks. Birds may also grow abnormal wing feathers, impeding flight. Of course, loons aren't alone: Methylmercury affects many fish-eaters, from otters to eagles to humans. Asks Evers, "If loons are in trouble, how will we fare?" ---Jennifer S. Holland PEOPLE AT RISK As industry grows world- wide, so does human exposure to methylmercury. Some U.S. states now regulate emissions, for good reasons. ■ Every year, one in ten fetuses, or about 400,000, is exposed to dangerous methylmercury levels in the womb, where the poison is more concentrated than in maternal blood. ■ Methylmercury exposure can affect IQ and lead to neurological damage and behavioral problems. ■ High-level exposure has been linked to mental retardation and symptoms of cerebral palsy. Loons affected by mercury are less likely to piggyback their chicks.