Song birds, mammals and amphibians alike are being exposed to toxic amounts of mercury, according to a report released by the National Wildlife Federation (NWF). Fish have long been blamed for bringing mercury into the food chain, and the Environmental Protection Agency has issued guidelines to pregnant women since 2004 warning them to limit their fish intake for this reason. But the NWF report highlights that the threat is much wider than that. Forest birds, raccoons, bats and bullfrogs are all being exposed to harmful levels of mercury.