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Wood thrush © Billtacular

Mercury accumulation, previously considered a risk for aquatic ecosystems, is also found in many animals living on land.

A new report, published by the Biodiversity Research Institute (BRI) and The Nature Conservancy, called Hidden Risk: Mercury in Terrestrial Systems of the Northeast highlights the Institute’s scientific findings about high levels of mercury contamination in songbirds and bats throughout 11 northeastern states, including New York.

“Our research shows that mercury still exists in the environment at high levels in places and in species we didn’t realize were contaminated just a few years ago,” said Dr. Tim Tear, New York director of science for The Nature Conservancy. “And many of these places and species occur in people’s backyards.”

What We Learned

Hidden Risk is the most complete synthesis of songbird and bat mercury data in the Northeast published to date. This report documents, for the first time, elevated levels of mercury in a wide range of songbirds and bats living in a variety of terrestrial ecosystems in northeastern states from Maine to Virginia.

Among the findings:

• Current environmental mercury loads have the ability to significantly reduce reproductive success in several songbird species of conservation concern in the northeastern U.S., including the saltmarsh sparrow and rusty blackbird;
• Bats also build up significant body burdens of mercury; individuals from multiple species from all 10 areas sampled in the northeastern U.S. exceeded the subclinical threshold for changes to neurochemistry;
• Mercury loading in songbirds is not only restricted during the breeding season; for some species, such as the northern water thrush, high levels of mercury accumulate during migration and in tropical wintering grounds.

Songbirds and bats, often referred to as insect eaters, are more accurately called insectivores because they eat a wide variety of invertebrate species such as spiders, snails, and worms, in addition to insects. Little is known about what the impacts of mercury are on these species that live at what we think of as the bottom or base of the food web. For the first time, this research gathered together studies that trace how mercury is moving through the terrestrial–or land-based–food web. This research highlighted that mercury is in many more food chains and food webs than we realized. Tear said “It is not just in lakes and ponds. It is in our forests and our estuaries. It is in our spiders and our backyard birds. It is in the lowlands and on the mountain tops. It is deep in the Adirondacks and it is in New York City.”

What Can We Do?

The Hidden Risk report calls for a number of management actions that can be taken to reduce the mercury risk in various terrestrial ecosystems:

• Greater investment in a mercury monitoring network. This would allow us to better assess the extent of this problem, and if current efforts to reduce mercury like the recent Mercury Air Toxics Standards (MATS) Rule that requires coal-fired power plants to update their mercury pollution control technologies, are enough to result in improving the areas that are damaged.
• Continued research to learn more about this issue. This includes altering some management practices to reduce mercury emissions.
• More support for local, regional, and global efforts to reduce mercury. There is no question that mercury is coming from multiple levels and no single level is enough.

“The recent U.S. EPA MATS ruling and release of the National Acid Precipitation Assessment Program Report to Congress: An Integrated Assessment underscore the fact that although efforts to reduce air pollution in the United States are working,” said Tear, “there is still much more work to be done.”