ALBANY – A 10-year study of Adirondack loons shows mercury contamination can lead to population declines because birds with elevated mercury levels produce fewer chicks than those with low levels, researchers said Thursday.
The report summarizes field research conducted from 1998 to 2007 by the Biodiversity Research Institute, headquartered in Gorham, Maine, and the Wildlife Conservation Society. The work, sponsored by the New York State Energy Research and Development Authority, gathered baseline data to monitor mercury and support environmental regulation.
Mercury contamination in the Adirondacks comes mainly from emissions from coal-fired power plants in the Midwest and elsewhere. In December, the Environmental Protection Agency finalized standards that require coal-fired power plants to update their mercury pollution controls.
Loons are fish-eating, diving aquatic birds about the size of small geese. The study found 75 percent of loons sampled were at a moderate to high risk from mercury in their blood, said Zoe Smith, director of the Wildlife Conservation Society’s Adirondack Program, based in Saranac Lake.
Loons with high mercury levels lack the energy to incubate their eggs properly and take care of their young. As a result, a loon with a high level of mercury produces 40 percent fewer young, the report said.
The researchers studied loons at 44 Adirondack lakes, taking blood and feather samples for mercury testing and observing their nesting behavior. They also tested lake sediment, water, plankton, crayfish and fish to document mercury contamination.
The study showed mercury contamination in the aquatic food chain increased significantly from plankton and crayfish to higher-level predators including loons. Loons in the southwestern Adirondacks were more likely to have elevated mercury levels than those elsewhere in the Park.
Loons on acidic lakes had higher mercury levels and lower reproductive success than loons breeding on non-acidic lakes.
Loons, which live 20 to 30 years, typically return from winter migration to nest on the same Adirondack lake from year to year. If that lake has a high mercury level, the loons also will have high levels because mercury stays in the body and builds up over time. Thus, loons are considered an excellent indicator species for the health of an aquatic ecosystem.
Besides mercury, loons also are harmed by lead poisoning from fishing sinkers and entanglement in fishing line, said Nina Schoch, who coordinates Adirondack loon projects for the Biodiversity Research Institute. People with motorboats and personal watercraft also harm the birds by causing crashing waves that damage lakeside nests, she said.
The Adirondack loon population has increased from about 800 to 1,000 in the 1980s to an estimated 1,500 to 2,000 today, said Schoch, who has been leading a citizen science-based annual loon census since 20 01.
That may seem to contradict the findings of the mercury study, but Schoch said it could be that reproduction by loons with low mercury levels could be offsetting the low reproduction by those with high mercury levels. Or, it could be that the population would have grown much larger if not for the mercury and other threats.
“Mercury,” Schoch said, “is definitely affecting the portion of the population with high levels.”