. People used to think that mercury pollution was a problem isolated to remote areas of the Northeast. No more.
Q. So, would someone see a bird or a bat acting strangely because of mercury pollution? Or is this something that data is telling you?
Evers: The effects are difficult to see in the field for the average observer. Mercury doesn’t create physical mutations, and an individual animal with mercury will probably die from predation first. But mercury is a neurotoxin that does impact wildlife behavior, and that behavior impacts their survival and reproduction. We focus on data to really quantify the impacts of mercury on the reproductive success of species.
For example, we quantified mercury impacts on the common loon. Common loons need to spend about 98 percent of their time on a nest incubating their eggs to have those eggs successfully hatch. We’ve quantified with over 5,000 hours of observation that loons with high mercury levels spend only 85 percent of their time incubating those eggs. So they spend less time in an incubation posture, and because of that, eggs do not hatch, and because of that, the species’ reproductive success goes down.
Q. Where is the mercury pollution still coming from? And what U.S. regions are of most concern?
Tear: Most of the research has really focused on the Northeast United States — an area that’s been really hard hit by acid rain, which makes mercury a bigger problem. But mercury pollution is happening all over the world. It comes globally from Asia, as well as nationally from power plants in the Midwest, to locally from waste incinerators. We’re going to need to address all sources of mercury to be successful in stopping these impacts.
Q. And in different habitats, right? Most people in the United States who know about mercury in nature know about it through warnings about the fish they eat.
Evers: Yes, there’s been a paradigm shift in new findings. In the past, most of the scientists assessing risk from mercury in an ecosystem would be looking at fish-eating birds and fish-eating mammals — because we knew methylmercury (the organic form of mercury) moved through the food web in aquatic organisms. But there’s been a missing link in looking at mercury in terrestrial ecosystem food webs and looking at how species that eat insects and spiders — what we call “invertivores” — can be affected.
In the invertivore food web, the key pieces are no longer fish, but spiders. A bird that eats a spider that ate a spider that ate a fly — that’s four different changes in the trophic food web. We’ve established that a little songbird like a northern waterthrush or a sparrow that eats spiders can actually be higher up in the food web than a bald eagle, which eats fish — and so that songbird has more mercury in its body than does the eagle.
Tear: We’ve also discovered that mercury is in many more food webs than we realized. It is not just in lakes and ponds. It’s in our forests, our estuaries; it’s in the lowlands and on the mountaintops. It’s in the spiders in the Adirondacks, and it’s in backyard birds in New York City.
Q. You mentioned effects on reproductive success. What are some of the other impacts of mercury on terrestrial wildlife?
Evers: For example, bird song is affected. Two recent studies show that birds with high mercury can’t hit the high notes, and their songs are simplified. I also worry about long-distance migration, because high mercury has been shown to affect the symmetry of development. If a bird’s left wing is 5 percent different in shape than its right wing, that bird is going to fly in a crooked way to compensate for it, which requires more energy to make a flight of thousands of miles to its wintering area. Ultimately, that’s going to affect its survival.
Q. That’s sad. But ultimately, why should humans care?
Tear: First, if you care about the environment and you care about birds and bats and bugs, then you should care that many of these animals are being heavily impacted.
But the second answer is that the neurotoxic rain that contains mercury falls on humans as well as wildl