By SAM INGLOT
Capital News Service
LASNING — Scientists are finding more Great Lakes birds with high levels of mercury in them.
A recent report by the Biodiversity Research Institute says the increased levels are found particularly in songbirds that rely on insects for food.
Aquatic birds still face the greatest risk for mercury exposure, said Joe Kaplan, a researcher with Common Coast Research & Conservation, a nonprofit loon research group based in Hancock.
Two factors impact how mercury affects a bird, he said: the amount of mercury it’s exposed to and the bird’s sensitivity to the metal.
Loons will always be exposed to more mercury than songbirds because of their fish diet, Kaplan said. However, loons have a low sensitivity to mercury compared to their woodland-dwelling counterparts.
Until recently, mercury contamination was seen as a problem for water-dwelling birds with fish-based diets. Studies of mercury in loons have been done for decades.
In Michigan, bald eagles, common loons and trumpeter swans are the only birds routinely tested for metals like mercury, lead and selenium, said Tom Cooley, a wildlife biologist at the Department of Natural Resources Wildlife Disease Laboratory.
Swans, Cooley said, are exposed to mercury because they nose around in the bottom sediments of lakes and rivers looking for aquatic plants to munch on.
Using a fluoroscope, or as Cooley calls it, “a poor man’s X-ray,” biologists scan the livers of dead birds that have been brought into the laboratory.
The aim, he said, is to determine what kind of adverse effects or behavioral changes the metals may induce in the birds.
Songbirds have not been heavily studied for mercury exposure, said Allyson Jackson, manager of the forest bird program at the Biodiversity Research Institute. The Maine-based organization researches emerging threats to wildlife and ecosystems.
Higher levels of mercury can cause brain damage, she said. And at low levels there tends to be a decline in reproductive success.
Kaplan said the reason songbirds have elevated exposure could be that they eat insects associated with aquatic environments. And unlike loons, they may be unable to release the mercury through their feathers.
Loons get rid of mercury through their feathers, like humans do through their hair. But for birds with high sensitivity, he said, that’s probably not the case.
Mercury can be particularly harmful when birds migrate because migration is the most physically demanding time in a bird’s life, Kaplan said.
The study said migration accounts for nearly 75 percent of annual mortality rates among some songbirds. Feathers stop growing during this time, and birds must complete a migration before they can molt and release some of the mercury.
Depending on species sensitivity, that’s when most problems occur.
The institute said research into the problems of songbirds with high levels of mercury is an on-going process.
Great Lakes bird species vary in the degree of sensitivity to mercury.
- American kestrel, white ibis, snowy egret, osprey tricolored heron
- clapper rail, tree swallow, common grackle, ring-necked pheasant, royal tern, sandhill crane, Anhinga brown pelican, Canada goose
- Hooded merganser, laughing gull, lesser scaup, common loon, mallard, double-crested cormorant
Source: Biodiversity Research Institute
Sam Inglot writes for Great Lakes Echo.
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