by Susan Sharon
MPBN news story
A new report by the Gorham-based Biodiversity Research Institute and the Nature Conservancy finds high levels of mercury contamination in songbirds and bats throughout 11 Northeastern states. While the risk of the pollutant to people is well documented through the consumption of fish, this study finds that mercury concentrations in a wide-ranging number of birds and bats are enough to cause physiological and reproductive harm. And it’s expected to cause a shift in ecotoxicological research and monitoring.
The research began almost by chance at a Superfund site on a river in Massachusetts about 11 years ago. Dave Evers of the Biodiversity Research Institute and a team of scientists were trying to determine the effects of mercury contamination on kingfishers, fish-eating birds that were thought to be at risk.
By accident they also netted several Red wing blackbirds, which typically don’t eat fish but consume mostly insects and spiders.
“And so the field team, at the time, they were taking the Red wing blackbirds out of the net and were planning to just let them go,” Evers says. “But instead I happened to be there and I said let’s make sure we get some blood samples and feather samples and just check to see what they’re like. And lo and behold we found that they were, on average, seven times higher in their blood and mercury concentrations versus the kingfishers that are eating fish.”
Evers says that prompted a wider study of nearly 80 species of songbirds and bats–nearly 2,000 individuals all together. And what they found is that songbirds that breed in wetland areas have higher levels of mercury than songbirds in non wetland areas.
The reason is because mercury converts to a more toxic form – methylmercury in these places. It is emitted to the atmosphere through coal-fired power plants and incinerators, falls to the ground in an inorganic form, and when it falls near lakes and wetlands, bacteria covert it to organic methylmercury, where it enters the food chain and undergoes “biomagnification.” In other words, mercury increases as it works its way up.
“Just think of a songbird, a warbler, eating a spider that eats a fly, is the same thing as a loon eating a bass, eating that fly,” Evers says. “And so even though that little warbler is much smaller than a loon it’s at the same level in the food web so that biomagnification of methylmercury is the same, or can even be higher, because a songbird eats a spider, eats a spider, eats a fly – you can see there’s four levels of exchange there, and that’s very important.”
The study, titled “Hidden Risk” finds that some habitats and species are of special concern. Estuaries, for example, have some of the highest levels of methylmercury and bogs, so species that live near and around these habitats and that eat fly larvae and spiders are especially at risk–the salt marsh sparrow, the rusty black bird and, surprisingly, even the Bicknell’s Thrush found at high elevations not commonly associated with wetland areas.
“Mountain areas also tend to have a lot of fog, and so if you can think of mercury in the air, in the fog, in the water droplets, coming down on those trees and coming down into the habitat in the mountain area, it’s kind of infusing that area with mercury more regularly than not,” Evers says.
Evers says researchers also studied the little brown bat, a ubiquitous, nocturnal creature in the Northeast that also feeds on insects but that is increasingly falling victim to white-nose syndrome. Because bats are long-lived they have the potential to accumulate high levels of mercury, which can compromise their immune system and make it harder to ward off infections like white-nose syndrome.
He’s also worried about the effects on neo-tropical migrants, such as scarlet tanangers or indigo buntings, species that are more difficult to study because of the distances they fly, and that are facing declines of up to 90 percent over the past few decades for reasons that are not clearly understood.
“Those are the sort of questions that we’re indeed looking at right now,” he says. “I think understanding the effects of mercury is also crucial and we’ve just published a paper that looks at how much mercury is too much for a bird. We now know if we are given a mercury concentration in the blood or the egg or the feather of a songbird, we can relate that to the percent nesting failure for songbirds. I think that’s very important to know how much is too much and we do know that now.”
Evers says it’s also important to know that, despite the findings of how pervasive the neurotoxin is in the environment and how great a threat it poses to wildlife and to human health in the way of cardiovascular disease, asthma and developmental problems, efforts are underway to reduce mercury in the environment.
“The United Nations, an environment program, is working on a global mercury treaty right now,” Evers says. “They hope to have that ratified and signed by 170 countries in 2013. So there are big efforts to reduce mercury in our environment and there’s no reason for us to put our hands up in the air. And the good thing is, once mercury is being taken out of a system that system can respond favorably within several years.”
Evers credits Maine Sen. Susan Collins and Congresswoman Chellie Pingree with sponsoring legislation to provide for a national mercury monitoring network.
