Thousands of Birds Migrate to the Arctic—Unfortunately, So Does Mercury

How pollution from thousands of miles away finds its way into animals at the top of the world.

August 11, 2016
A semi-palmated sandpiper on the coast of Alaska

Gregory "Slowbirdr" Smith/Flickr

The semipalmated sandpiper is a pint-size shorebird that flies thousands of miles from South America to raise its chicks on Alaska’s northern coast. When the tide goes out, this predator hops out into the shallows, stabbing its beak at aquatic insects and crustaceans to refuel after its long flight and beef up for breeding season.

For the most part, the bird does pretty well up there, but scientists recently found something troubling about this sandpiper: For such a little guy, it contains a whopping amount of mercury. The researchers, who published their findings this month, tested the mercury content of feathers and blood of migratory birds that use the shores of northern and western Alaska as breeding and feeding grounds. The semipalmated sandpiper topped the list for contamination. In fact, all the birds that prefer to dine in the state’s wetlands and aquatic habitats seem to pick up significantly more mercury than the birds that forage inland and upland. Those birds on the interior showed mercury contamination, too, but at lower levels.

This didn’t exactly surprise the researchers. The types of microorganisms that can metabolize inorganic mercury in the environment, turning it into methylmercury (the kind that accumulates up the food chain), are more prevalent in wetland and aquatic ecosystems.

But wait—where is all this inorganic mercury coming from? It’s not as if it’s so cold in Barrow, the country’s northernmost city, that thermometers are bursting and leaking their neurotoxic contents into waterways. But you can, sort of, blame it on the weather. According to lead author Marie Perkins, a wildlife toxicologist at Montreal’s McGill University, the mercury accumulating in Arctic waterways arrives via global atmospheric patterns. Most of that mercury, as you may know, is first sent into the heavens by human activity, often as a by-product of coal-burning power plants and artisanal and small-scale gold mining.

In its atmospheric form, mercury is relatively stable and can remain up there in the air for years, until something gives it a shove back to earth. One of those somethings is an element called bromine, which, alas, is released by sea ice when it melts. Bromine reacts with mercury in the atmosphere, causing it to oxidize, plummet, and get swept up into the food web.

Perkins and her coauthors note that mercury can create all kinds of problems in birds. While ingesting tiny amounts of the toxin doesn’t kill them immediately, the metal can build up in their tissues to the point where it messes with biological processes. A study of Carolina wrens linked mercury exposure to reproductive impairment. Another study found lower reproductive success and weakened immune systems in tree swallows with high mercury levels. The impact may be even more significant for migratory birds, Perkins says.

“During migration, these birds burn energy reserves, including muscle and other tissues,” she says. As a bird flies long distances, its metabolism unlocks the toxin from those tissues, allowing the mercury to “make its way to sensitive organs, like the brain, during this already demanding time.”

Birds that migrate to and from South and Central America, like the semipalmated sandpiper, might even get a double dose of mercury, since these areas are rife with artisanal and small-scale gold mining, activities that come with a hefty heavy-metal legacy.

How the accumulation of this poison is affecting these birds individually is unknown, but any reduction in reproduction and migration could have population-wide impacts. Shorebirds are the most abundant and diverse group of animals on Alaska’s North Slope, Perkins says, and that makes them crazy important for the ecosystem.

The seabirds chow down on innumerable invertebrate species, and then, in turn, they become dinner for other birds, such as jaegers, snowy owls, and peregrine falcons. Red and Arctic foxes also feast on their eggs and chicks. Any disruption to the sandpipers and their ilk on Alaska’s shorelines could ripple inland.

As you read this, the Arctic’s sea ice is breaking apart as it does every summer. Swirling above is a whole a lot of mercury waiting for its bromine anchor. This cycle will continue for some time, but the less coal the world burns, the less heavy metal our little sandpipers and plovers and godwits and falcons and owls and foxes will ingest in future springs. 

This article was made possible by a grant from the Jonathan and Maxine Marshall Fund for Environmental Journalism.

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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