Mercury causes ‘foggy headed’ loons to fail as parents, possibly threatening their future

STANDISH, Maine — When Thom Watson is showing tourists or budding sportsmen around the lakes of Maine, loons are the prized sightings.

“In terms of Maine folklore, when I’m with clients, I love to see them, love to hear them and, maybe most of all, love to see the reaction of someone who is hearing them for the first time,” said Watson, a Registered Master Maine Guide and former state lawmaker who served as House chairman of the Legislature’s Inland Fisheries and Wildlife Committee.

Volunteer annual loon counts in recent years indicate the state’s adult population of the iconic birds, with their haunting nighttime calls so vividly associated with the Maine wild, is still strong. But some researchers believe those steady figures are cloaking a persistent increase of environmental mercury, which doesn’t kill adult loons outright, but sets the stage for a potentially catastrophic population drop-off down the road.

“My fear in Maine is that it’s going to be too late before we realize the loons are disappearing,” said Camilla Fecteau, a biology instructor at St. Joseph’s College in Standish, where she’s scheduled to offer a 7 p.m. talk on Tuesday titled “Common Loons: Preserving a symbol of Maine wilderness.”

Mystery still fogs much of what scientists in the state know about loons and the dangers creeping into their environment. Fecteau notes that nobody is really sure how many loons there are in Maine, because annual bird counts don’t include lakes and ponds in the northern half of the state. The unscientific data Mainers do have show puzzling oscillations in the year-to-year numbers of chicks.

The uncertainty surrounding loons, and data used to analyze their health as a species, leave some biologists nervous, especially considering what they can quantify: That certain levels of mercury reduce the abilities of adult loons to rear offspring. And that Maine loons are being found with those levels in their blood.

“If loons are not able to at least replace themselves in the population, they’re going to drop off,” Fecteau said. “It’s simple math.”

A population in peril?

Fecteau said a mercury level of three parts per million in the blood of loons is the threshold at which the birds begin to struggle in their reproductive cycles.

“Three parts per million doesn’t kill loons,” she said. “It makes them sort of foggy headed. Mercury’s a neurotoxin. Maybe a loon that’s affected by this level of mercury doesn’t pay enough attention to their chick when it’s freshly hatched and vulnerable, or maybe it stays off its nest for a little too long, or maybe it’s less aware of predators in the area. It makes them less attentive as parents, and so in return, scientists are finding it’s having an affect on their productivity.”

A comprehensive study by Dr. David Evers, Fecteau’s graduate adviser and executive director of the Gorham-based BioDiversity Research Institute, found mercury levels in adult Maine and New Hampshire loons ranging from 1.3 ppm to 10.8 ppm. The levels were also climbing, creeping up by 8.4 percent per year over the 18 years of research included.

Fecteau said the northeastern United States has the highest levels of mercury in the environment of any location where common loons live, in part because the region is “downwind” meteorologically from most of the nation’s coal-fired power plants, which combine to be the top source of mercury pollution in America.

Mercury combines with organic materials in the natural environment to become the more dangerous methylmercury, where it is absorbed by plankton, which is then ingested by fish. Loons then eat the fish. Loons are considered an “indicator” species for environmental dangers, Fecteau said, because the toxin levels multiply up the food chain and adverse effects of the buildup can be recognized in the birds earlier than in the smaller species.

“I’m sort of conflicted about whether our loon population is in peril or not. But we do have a mercury issue,” said Barry Mower of the Maine Department of Environmental Protection’s Division of Environmental Assessment.

Since 1997, the state has maintained an advisory warning children and women of child-bearing ages not to eat warm-water fish caught in any of Maine’s inland waters because of the increased mercury levels. It might stand to reason that if eating Maine fish is unhealthy for humans, it would be even worse for loons, which are smaller, have less diverse diets and have ignored the advisory since the onset.

The reason Mower is conflicted is that, despite that reasoning, the loon population in Maine seems to have grown significantly over the past several decades.

The loon boom — and bust?

In 2010, the most recent year in which the Maine Audubon Society’s annual loon count data has been compiled, the project’s 900-plus volunteers found approximately 3,220 adult loons on 300 lakes and ponds in the southern half of the state.

“That’s an all-time high,” said Susan Gallo, head of the society’s Loon Project.

It’s about double the number of loons counted in the same area in the mid-1980s, and Gallo said some people believe Maine has the maximum number of loons the state’s ecosystem can handle.

But others think the population of Maine loons is just a tower of cards — big, but fragile, and in danger of collapse.

Gallo said the high number of adult loons counted annually can be a distraction from the less convincing number of chicks. She said the yearly chick figures vary wildly from 150 to 400, and seem not to steadily grow over time like the numbers of adults, vexing researchers who assume that more adults would naturally create more offspring.

“It’s a little bit deceiving to say we have a healthy loon population,” Gallo said. “The adult numbers go up, and when people see the numbers go up, they assume the population is healthy. But why aren’t there more loon chicks?”

The reason? A greater and greater percentage of the adult loons each year are nonbreeders. Some are simply not finding mates, and others are failing as parents to make strong nests or raise the young ones.

“Maybe they’re not successful because they’re high in mercury,” Gallo said of the foggy headed symptoms that would trigger difficulties on the loon dating scene as well as child-rearing duties. “Maybe they’re not successful because they don’t have room.”

In either case, Gallo said it’s unlikely the adult loon populations will continue to so dramatically outpace the chick populations, for obvious reasons. The loon count could be heading for a cliff as the adult bachelors and bachelorettes die off and have fewer heirs to replace them. The trouble is, it may take years before that effect is realized.

“They’re really long-lived birds,” she said. “They live 25 to 30 years — maybe longer — and they don’t breed until around 7 years old. There’s definitely kind of a lag time, from when they hatch to when they’re supposed to reproduce. If we had a disastrous hatch year, it would be 10 or 12 years later before you start seeing population impacts.”

Gallo also noted that the species continues to face myriad other threats, such as shorefront development, the emergence of new fungal diseases, boat wakes and lead fishing weights, which are still used despite Maine regulations against them and are often fatally eaten by diving loons.

That pile-up of hazards could weaken the loons enough so that they’re less able to rebound once their reproduction inequity comes full circle some years down the road.

“Mercury itself may not be the end of loons in Maine,” said Gallo, reached Friday while attending the annual Northeast Loon Study Working Group meeting in New Hampshire. “Lead sinkers may not themselves be the end of loons in Maine. But when you add them all up, there’s definitely a risk to loons. I’m not saying there will be an end to loons in Maine … but there is that potential for something catastrophic.”