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Looking for Lessons from Loons

By studying the behavior of these elusive birds, scientists may also learn about the effects of mercury pollution on wildlife

  • John Carey
  • Aug 01, 1996
The drama on Lake Aziscohos in western Maine last July began with an eerie midnight duet. From a small boat, biologist David C. Evers played a recording of the cry of a common loon. From the darkness came an answering wail. One of Evers' helpers stabbed the darkness with a searchlight. There! The loon was caught in the beam, head feathers shimmering. Little did it know that it would soon help biologists probe both the mysteries of loon behavior and questions about pollution from a toxic metal, mercury.
Jeff Fair, an independent loon biologist, steered towards the curious bird. Dazzled by the spotlight, the loon couldn't see the scientists. With the boat just 2 feet away, the bird dived for safety--right into a net. The athletic Evers lifted his subject onto the boat. Fair wrapped its head in a towel, and Evers attached leg bands, snipped a few feathers and stretched out one short, muscular leg so colleague Erin Harshberger of Tufts University could draw blood. The samples would later be tested for mercury. Then Evers weighed the loon and lowered it back into lake.
Until Evers developed a twist on this capture technique in 1989, for the most part adult loons had eluded biologists trying to capture live birds for up-close study. Sure, their shoreline nests are simple to observe. So too are the birds' courtship dances and water-splashing territorial fights between males. And the birds' helplessness on land has long been well known: Loons need a take-off run of as much as a quarter-mile across open water. Many a loon has mistaken a rain-slicked road for a lake, crash-landed and been unable to get into the air again.
But scientists still can't determine the age of an individual bird; it's even hard to tell two birds apart. "Loons are great liars,'" says biologist Fair, who has studied them for 18 years. More than once, he has been convinced that a pair of loons has given up on nesting for the year--only to spot the birds weeks later with a couple of chicks. Or a chick may seem to disappear. "You put a zero down in your notebook and feel forlorn," says Fair. "Next day, you look across the lake in the morning mist, and there is the chick."
Not only does much remain to be discovered about the birds' natural history, says Evers, "There is a tremendous interest in loons as an indicator of habitat quality." Because the birds perch atop the aquatic food chain, they become a repository for chemicals that humans spew into the world. Fair calls the birds "windows on our environment."
The view they provide is sobering. Even in remote lakes of Canada, Evers and others have found that loons harbor surprising amounts of mercury. The big question is: How much is too much? Scientists do know that high doses of one of its many chemical forms (methyl mercury) cause everything from birth defects and mental retardation to kidney damage and death in humans and other creatures. In Minamata, Japan, in the mid 1950s, hundreds of human deaths and illnesses resulted from consumption of mercury-contaminated seafood. And during a famine in the early 1970s, Iraqis ate seed grain coated with methyl mercury to protect it from pests. More than 450 people died, and more than 6,500 others suffered neurological problems.
Such disasters have been rare. But as Evers' loon study and other analyses have found, mercury is found in worrisome levels in many places around the world. "Mercury is one of the most, if not the most, important chemicals we are concerned about," says Melissa McCullough, coordinator of the Environmental Protection Agency's Great Waters Program, which is assessing pollution threats in the Great Lakes, Lake Champlain and certain coastal waters.
Though mercury vapor can be deadly, in aquatic ecosystems the elemental metal is relatively harmless. Only when bacteria chemically transform it to methyl mercury does it become especially dangerous--and begin working its way up the food chain. First, the methyl mercury is taken up by zooplankton. Then the plankton are eaten by larger critters, and so on, the mercury accumulating at higher levels in larger organisms. For example, concentrations of mercury in northern pike from northeastern Minnesota lakes are 225,000 times higher than in the water around the fish.
One 1990 study in Wisconsin found that many Chippewa Indians have blood mercury levels above 5 parts per billion, high enough to cause developmental problems in fetuses. And 37 states--virtually all that have looked--have found enough mercury in local fish to issue warnings about consuming them. Michigan, for example, recommends that people eat no more than one meal a week of bass, perch, walleye and other fish from the state's inland lakes. The Food and Drug Administration warns pregnant women--and women of childbearing age who may become pregnant--to limit consumption of shark and swordfish to no more than once a month.
Still, proving that mercury at loose in the environment harms living things, particularly humans, is a tough task. One recent study in the Seychelles Islands found that young children of women who ate low levels of mercury in fish when pregnant did not seem affected by the metal. But preliminary results of another, ongoing Danish study indicate significant developmental effects among somewhat older children of mothers that consumed mercury-contaminated seafood when pregnant. And some of the possible effects (such as small drops in cognitive ability) could be difficult to measure. "Even the researchers who did the Seychelles studies point out their results were inconclusive," says Tim Eder, team leader of NWF's water-quality program. "One thing is clear: Mercury is a dangerous substance, and there is already too much of it in our environment."
Dozens of studies of mercury in wildlife are underway, with subjects ranging from mink to mergansers. In one such study, scientists found high mercury levels in a small group of Florida panthers that eat fish-eating raccoons instead of the big cats' usual diet of deer and wild pigs. One dead panther had 100 parts per million (ppm) of mercury in its liver--enough to have killed it, according to the vet who did the autopsy.
Loons may offer the best clues about the extent and danger of mercury contamination, since common loons' summer habitat spans North America in a broad band from Washington state to Canada's maritime provinces. If so, much of the credit will go to Evers, now a Ph.D. candidate at the University of Minnesota and head of the private research group BioDiversity, Inc., in Yarmouth, Maine. Evers is building on earlier work conducted in the 1970s by biologist Jack Barr, then doing work for the Canadian Wildlife Service, who found that loons with 2 to 3 ppm of methyl mercury in their brain tissues were less frequent nesters, paid less attention to their nests and defended their territory less than other loons. Back then, Barr sacrificed his study subjects in order to measure their mercury levels.
Seven years ago, when Evers set out to band and observe common loons for his master's thesis, he discovered for himself why they have been called "great northern divers." With their powerful legs, big webbed feet and the ability to swim at great speeds underwater, the birds easily eluded him when he tried the techniques other researchers had been pioneering--such as spotlights at night and tape-recorded calls. Then, early one morning, Evers came upon a female with a chick. "As I approached," he recalls, "the bird started swimming away like usual." But then the chick peeped--and the parent swam toward it. "It suddenly hit me; I should mimic a chick," Evers says. "The bird turned back to the boat, and I caught it!" The technique doesn't always work. "Sometimes it seems like they're taunting us," says U.S. Fish and Wildlife Service biologist Philip Morrison, a frequent volunteer on Evers' expeditions. Still, Evers and colleagues have caught scores of birds in lakes from Alaska to Nova Scotia. Collaborators at Michigan State University test blood and feather samples for mercury.
So far, the researchers have found clear geographical differences in mercury levels: the farther to the East, the higher the levels. Loons in Alaska have low levels, only about 0.5 ppm. In the Great Lakes, loons average 1.1 ppm, in New England 2.3 ppm and in the Canadian Maritime Provinces 3.1 ppm. The data support the idea that, like other windborne pollutants, mercury wafts eastward from power plants, incinerators and other sources all across the country on the prevailing winds.
The loon captured on Lake Aziscohos that night last summer provided another clue: The bird's blood contained a high 4.6 ppm. One explanation, Evers says, is simply that the bird is old and accumulated the metal over many years. Another possibility may be the annual fluctuation in water level (as much as 20 feet) in the man-made lake, which is lowered every year. Such variation can make successful breeding difficult for loons, since shoreline nests can be either swamped or left high and dry. Not only that, exposing lake sediments to the air seems to speed the process by which bacteria transform metallic mercury into methyl mercury. Power companies are working to reduce the size of the fluctuation and are funding loon nesting platforms--as well as paying for some of Evers' research.
Are loons actually being affected by mercury in the environment at large? No one knows yet. Evers suspects the poison may cut the birds' normal 25-year life spans a few years short or alter behavior. "This is still just a guess on my part," he says. "I hope I'm wrong." Take the case of a Michigan bird Evers tested with a high 42 ppm of mercury in its blood. The next year, the loon returned and sired a clutch of eggs. Normally, a pair of loons shares egg-sitting duty. "But this male wouldn't sit on the eggs," recalls Evers. The female gave up on the nest. Later, biologists found the male's carcass with a hole in its breastbone, evidence it had been speared by the bill of another male during a territorial battle. Evers thinks mercury may have affected the bird's brooding behavior and slowed its reflexes enough to make it fatally vulnerable to its rival.
The good news is that the nation has already taken some important steps to fight mercury pollution, cutting back industrial discharges of mercury in the past two decades. But more recently, scientists realized that such discharges are only part of a larger problem. In the early 1990s, researchers such as Edward Swain of the Minnesota Pollution Control Agency proved that virtually all of the mercury reaching remote lakes around the world falls in rain or blows in on the breezes. The sources? Hundreds of power plants and municipal or industrial incinerators burning mercury-containing coal and waste.
The new findings galvanized activists to fight for a halt in the use of mercury in products that eventually end up in incinerators. Today, mercury has now been banned at the state level from most batteries and many other products. State and local governments have also worked with hospitals, dentists (who use mercury in fillings) and industries to lower the amount of the metal that goes into incinerators. A Michigan state task force, for example, has convinced the Big Three automakers to phase out mercury-containing switches in cars. (NWF's Eder was a charter member of the task force.) U.S. use of mercury has declined dramatically, from 2,357 tons in 1980 to 614 tons in 1993. The remaining big targets for activists are power plants, particularly coal-burning plants. The ultimate goal of environmentalists and public-health advocates: eliminating all man-made releases of the metal into the environment.
The loon studies will be an important indicator of how quickly and well that goal is reached. One possibly encouraging early sign is a loon comeback after the birds died by the thousands in the early 1980s on their ocean wintering grounds off the southeastern coast from Florida to Alabama. Biologist Laurence L. Alexander of the Florida State Museum in Gainesville believed the cause was mercury poisoning, although it was never proven.
As for the goal of deeper understanding of loon behavior, Evers has discovered that even though loons are typically monogamous, if a pairing fails to result in chicks, the parents may search for other partners. From year to year, about 20 percent find new mates and 13 percent stake out new territories. "It's a lot more switching than anyone would have thought before," says Evers. That may seem like a minor revelation, but it is exciting news in the slowly advancing study of loon behavior.
"What's unique is the chance to recapture the same birds year after year," says Evers. One key question is where chicks go after their first winter. So far, they don't often seem to return to the lakes on which they were born. "It could be there's more dispersal of the chicks than we had thought," Evers speculates. He hopes to solve this puzzle--and answer questions about migration routes and wintering grounds--by attaching satellite transmitters to loons starting this year.
Given all this new work, next time you hear a melody drifting ashore from some remote northern lake, you may well be listening in on another duet between science and its wild, wary avian quarry.
Business Week writer John Carey heard that duet himself last summer while accompanying loon researchers on Lake Aziscohos.

Mercury: How Much Is Safe? 
Most mercury that ends up in humans comes from fish, just like the mercury found in loons and other fish-eaters at the top of the food chain. The metal is clearly toxic, causing problems ranging from birth defects and mental retardation to kidney damage and death. But so far, scientists have not determined the levels at which mercury is harmful. The Food and Drug Administration recommends that people not eat fish with 1 part per million (ppm). Some states have other guidelines. Maine, for example, advises people to avoid fish with more than .43 ppm (about half the fish tested in Maine are within this standard). The numbers translate into guidelines about how many fish to eat from specific waters; if you fish, check with local health departments for relevant recommendations.

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