Photo © Carl Heilman / BioDiversity Research Institute

Mercury Connections

Using Bald Eagles as Contaminant Monitors

When scientists from The Nature Conservancy and the BioDiversity Research Institute found high mercury levels in songbirds in the Catskills last summer (read more about it in the last issue of Nature New York), they knew their work had only just begun. To determine if other species are also vulnerable to the effects of mercury contamination, scientists this summer are trading in mist nets used to capture small songbirds for sturdy tree-climbing and protective gear necessary to reach the forest canopy and handle the sharp claws of nesting bald eagles.

What is mercury and where does it come from?

Mercury is an element found in rocks in the earth's crust.  Through mining and industrial processes, mercury is brought to the earth's surface and used in manufacturing, electricity generation, and consumer products.  Eventually, the mercury is emitted into the air or discharged into the water as a byproduct of combustion or improper waste disposal.  Once in the air and water, mercury presents a threat to ecological and human health.

Why is mercury a threat to fish, wildlife, and people?

After mercury is emitted from a smokestack, it travels through the atmosphere, and is deposited on land and in bodies of water.  There, it is consumed by organisms and makes its way through the food chain.  Birds are particularly at risk for mercury poisoning because so many species consume mercury-laden fish.  They are also long-lived organisms and therefore accumulate mercury in their bodies over a long period of time.  Past research tells us that mercury can have adverse effects on individual birds was well as the population as a whole through changes in behavior, reproduction, and body chemistry.

What are some of the effects mercury has on birds?

As blood mercury levels increase in birds, the animals exhibit changes in reproductive, behavioral, neurological, and physiological functions that can prove detrimental to their survival.  Animals with elevated mercury levels tend to demonstrate lower reproductive success.  Fewer eggs are produced, and those that are exhibit reduced hatchability.  Affected animals tend to demonstrate difficulty flying and walking, and show a progressive weakness in their wings and legs.

Which birds are threatened by mercury in their environment?

The use of aquatic birds as indicators for mercury contamination has been a common practice for years.  The common loon, a large, long-lived species that lives almost entirely on fish and tends to nest on nutrient poor lakes, is one of the best indicator species for mercury contamination.  But scientists have discovered that both fish and insect-eating birds of the northeastern forests seem to be at risk.  One of the most significant discoveries made in studying mercury across the landscape is that mountain dwelling songbirds (insectivores) appear to be affected as well.

What is being done to study this threat?

Recently, The Nature Conservancy joined forces with BioDiversity Research Institute (BRI) to evaluate mercury levels in songbirds found in the Catskills region of New York.  Findings indicated high mercury levels in several songbird species, raising further concerns about high-risk species such as Bald Eagles.  Therefore, The Nature Conservancy and BRI are partnering to extend ongoing work to include sampling of eagles in the Catskills region.  BRI currently monitors mercury levels in loons, eagles, and other wildlife throughout Maine and parts of New Hampshire.  In addition, The Nature Conservancy is involved in long-term monitoring of surface and groundwater mercury, soil and sediment profiles, and invertebrate and fish sampling, all in an attempt to make connections between emissions that occur across the continent and the human and ecological impacts these emissions may have.

How is the sampling taking place?

Highly skilled climbers ascend the tree and lower five to six week-old bald eagle nestlings to the ground, where they are sampled for blood and feathers, banded with colored leg bands, and given an overall health assessment.  The animals are then sent back up to the nest in a bag.  The adults, though sometimes a bit upset by the ordeal, do not typically attack or dive-bomb the tree climbers.  The biologists leave the area immediately after sampling and are sure to visit only those nests that have been properly monitored throughout the nesting season to avoid visiting nests during sensitive times.

For more information about mercury sampling and the Conservancy's work in The Catskills, please contact Alan White at (845) 586-1002 or awhite@tnc.org.