Holland, Jennifer S.
Mercurial Loons
National Geographic Magazine, Vol. 216, #5, Nov. 2009, Environment Section
National Geographic Society
Original Date
  • Bookwood Historical Collection, Star Lake
  • UW Madison/Wis Hist Soc

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 waterways mercury can turn into the even more insidious methylmercury and infiltrate the food chair, 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 [Photo in original], 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 are alone: Methylmercury affects many fish-eaters, from otters to eagles to humans. Asks Evers, "If loons are in trouble, how will we fare?"

[Photo of loon piggybacking chick, with caption, "Loons affected by mercury are less likely to piggyback their chicks."]