The Case of the Disappearing Ducks
Why are scaup and scoters in decline when other waterfowl are on the rise? The answer may lie in Canada's remote boreal forest
ERIC BUTTERWORTH seems unperturbed as he sits hunched in a small plywood blind near a spruce-fringed pond in northern Alberta. Butterworth--who is helping to census waterfowl in Canada's northern, or boreal, forest--barely acknowledges the cloud of mosquitoes trying to probe his skin.
The biologist, who works for the conservation group Ducks Unlimited, is far more interested in what is on the pond. Ducks of various species putter about the water, many with young paddling behind them. "There's a goldeneye," Butterworth mutters, a pair of binoculars jammed into his ocular orbits. "Three ringnecks over there. Wigeon. Two more ringnecks. One Scaup. Ringneck."
Butterworth removes the binoculars from his eyes. "I'm seeing mostly ringnecks out there," he says. "Very few scaup. Twenty years ago, the ratio would've been reversed. So what's going on? That's what we're trying to find out."
Butterworth's perplexity stems from a troubling decline in several species of scaup and scoters--diving ducks that nest in the boreal forest in the summer and were once extremely abundant.
Since 1978, the population of greater and lesser scaup has dropped from 6 million to 3.4 million. North America's three scoter species--white-winged, surf and black--have plummeted from about 1.6 million in the 1960s to about 720,000 today.
"What's happening to scaup and scoters is extremely alarming," says biologist Stuart Slattery, a colleague of Butterworth's at Ducks Unlimited. "Greater and lesser scaup are the only common species of North American ducks to show negative population trends since 1987."
Illustration: © DICK GAGE
BIG GREEN: Scaup, scoters and other ducks nest in the boreal forest, a vast ecosystem that covers much of Canada (map above) as well as Alaska, Scandinavia and Russia.
Conservationists point to several possible culprits in the case of the disappearing ducks. Chief among these are logging, agriculture, and oil and gas development in the boreal forest--a vast landscape of conifers and wetlands that plays a vital but largely unappreciated role in the life cycles of waterfowl and many other wild creatures. The list of suspects also includes two at the southern end of the ducks' migratory journeys: pollution and exotic species. Global warming has been fingered, too. Or maybe it's not a single perpetrator. "I think you're looking at a combination of problems," says Robert Clark, a researcher with the Canadian Wildlife Service. "One thing's for sure--we're seeing large-scale environmental changes on the breeding and wintering grounds."
The feathered victims of this whodunit, scaup and scoters, are among the most distinctive of Northern Hemisphere ducks. Greater and lesser scaup are similar in everything but size. Males have dark heads and white torso plumage striated with gray herringbone. Females are drabber, with a white patch at the base of the bill. Both have pale cerulean bills, accounting for their common sobriquet: bluebills. In the winter, greater scaup are usually found in bays and estuaries along both coasts. Lesser scaup generally prefer fresh water, and many overwinter on lakes and marshes across the continent.
All three scoters are large, robust sea ducks. During the fall migration, they fly as far south as Mexico. In the winter, flocks of scoters are often seen lolling around piers and beaches, foraging for shellfish and crustaceans.
Photo: © DARIN LANGHORST (DUCKS UNLIMITED CANADA)
BOREAL FOREST: Sprinkled with wetlands such as Oscar Lake in Canada's Northwest Territories (above), the remote forests of spruce and aspen harbor millions of waterfowl each spring and summer. This little-known but vital habitat is also the year-round home of wolves, bears, moose, elk, caribou and many other creatures.
Most scaup and scoters, along with many other species of waterfowl and migratory songbirds, wing their way north to Canada's boreal forest each spring to breed. Although largely unknown outside of northern latitudes, the wetland-stippled network of spruce and aspen that comprises the boreal forest is the world's largest terrestrial ecosystem. Ringing the globe south of the Arctic from Canada to Alaska to Russia to Scandinavia, it covers 11 percent of the Earth's land surface.
In North America, these remote woodlands shelter such mammals as moose, timber wolves, grizzly and black bears, woodland caribou, lynx, martens and fishers. The boreal forest is also a hotbed of waterfowl brooding activity, running a close second to the prairie pothole region of the northern Great Plains for the title of the continent's biggest duck factory.
Despite its importance to wildlife and its remoteness, Canada's boreal forest faces several threats--particularly in its more accessible southern regions. Oil and gas development, agriculture and logging are changing the nature and diminishing the richness of this crucial ecosystem.
Superficially, logging may seem the greatest problem. After all, if you clear-cut all the trees, you don't have a forest. Michael Brune of the San Francisco-based Rainforest Action Network calls logging the "single biggest threat" to the boreal forest in eastern Canada. "The Ontario provincial government is proposing to allow clear-cuts of 25,000 acres," says Brune. "Sixty percent of Ontario, Quebec and northern Manitoba are scheduled for clear-cutting in the next seven to ten years."
Some scientists say a certain degree of timber-harvesting in the boreal forest is tolerable. "The boreal forest is considered old-growth at 100 to 150 years," says Gary Stewart, a biologist at Ducks Unlimited who is overseeing the group's science and conservation efforts in Canada's western boreal forest. "Spruce and aspen don't live much longer than that. This is a forest that thrives on disturbance, mainly fire and beaver flowages." And some timber firms are increasingly willing to minimize their environmental impacts, says Stewart. "They replant. They put the roads to bed. They try to minimize erosion and disturbances to watersheds. If it's done right, timber harvesting doesn't have to have a huge impact on the forest."
Photo: © JOHN DE VISSER
WELL OILED: In addition to vast timber reserves, the boreal forest also has large stores of natural gas and petroleum, as these oil pumps in Alberta demonstrate. Clear-cutting, road building and oil and gas drilling are all on the rise here, and changing the character of this once-pristine wilderness. Some experts believe resource extraction, as well as farming in southern parts of the forest, are to blame for the fall of the greater scaup and its kin.
Far bigger problems, says Stewart, are agriculture, and petroleum and gas development. As for the impacts of the former, the biologist points out, "Once the woods are cleared for pasture or grain fields, they don't go back." The impacts of the latter two are especially apparent north of Edmonton, in Alberta's oil patch. Viewed from a helicopter, these woodlands look moth-eaten and sickly. Seismic lines--avenues gouged out of the canopy to allow geologic tests--spiderweb the landscape. Roads interweave with the seismic lines. Thousands of five-acre pads, each supporting an oil pump or gas well, pockmark the terrain from horizon to horizon. Every now and then spill sites hove into view: Some are ponds of oil, others splotches of blackened sod.
While the prime boreal forest nesting grounds are mostly north of Alberta's oil patch, it seems to be only a matter of time before large-scale extraction spreads north. Gas wells are already operating on artificial islands in the Mackenzie River, and seismic lines--the harbinger of hydrocarbon extraction--are creeping through the wilderness. In the winter of 2000 2001, more than 700 miles of seismic lines were carved through the Mackenzie Delta alone.
All the construction required by the hydrocarbon industry--roads and culverts, pads, pipelines, seismic lines--may be interfering with the productivity of the forest at its most elemental level, experts say.
"Water levels of nutrients--especially potassium and phosphorous--are very high here, which accounts for the tremendous quantity of invertebrates," observes Kevin DeVito, a scientist at the University of Alberta who is studying the province's boreal woodlands. All those tasty invertebrates--insects and their larvae, tiny crustaceans, mollusks, myriad worms--account for the tremendous abundance of waterfowl and other species. "The nutrients are contained primarily in groundwater rather than surface water," says DeVito. "There are concerns that development could block groundwater and nutrient flows, particularly in areas with clay soils."
That's particularly germane for nesting scaup and scoters, which thrive in heavily wooded boreal wetlands that are high in nutrients. The abundant ringneck ducks, on the other hand, may be able to glean a living from wetlands that would starve a self-respecting scaup or scoter.
So are ringnecks thriving because they are more adaptable? It's possible. But so far, there is no direct evidence that scaup and scoters are hypersensitive to oil or timber development in their broodlands. And some scientists point out that there may be other reasons for the ducks' decline--such as global warming.
"As it gets warmer up in the boreal forest, wildfire frequency could be affected," says Clark. "More frequent, hotter and bigger fires could reduce nesting cover and might have an impact on nutrient availability in the wetlands."
Warmer winters could also benefit boreal forest predators. "If you have greater numbers of predators surviving the winter, depredation of nesting ducks and their young could increase," says Clark.
Global warming may also work against ducks on their wintering grounds by reducing marine upwelling--the transport of cold, nutrient-laden offshore water into nearshore areas. Fewer inshore nutrients mean less food for birds and fish.
Pollutants may also be a factor, Clark says. "Scaup and scoters feed heavily on shellfish, so contaminant loads may be affecting them on the estuaries and coastal areas," he says. "Exotic mollusks like zebra mussels and Asian clams [which are invading U.S. waterways] can concentrate contaminants more efficiently than native mollusks, so that may be exacerbating the problem."
In fact, there is a growing body of evidence that contaminants in the winter food web may play a crucial role in the declines. San Francisco Bay, a primary destination for wintering scaup and scoters, is emblematic of the problem. This huge estuary teems with crustaceans and mollusks--favorite foods for diving ducks. But it is a system that is tainted as well as biologically rich. Selenium pours into the bay from refineries along the eastern shore and from the San Joaquin River, which traverses miles of selenium-loaded cropland. The remnants of spilled gasoline and oil also find their way into the water column, particularly after rainstorms. In addition, mercury, cadmium, zinc and copper flow into the bay from a variety of sources, including defunct cinnabar mines and the computer industries of Silicon Valley. All those contaminants end up in the mollusks and fish. And perhaps in the ducks that eat them.
Initial research in duck breeding areas hasn't shown this. "Some early studies on lesser scaup conducted in the parklands [lightly forested prairie] of Alberta didn't show significant levels of contamination in body tissue," says John Takekawa, a U.S. Geological Survey wildlife biologist in Vallejo, California.
Photo: © TOM VEZO
FOREIGN AGENTS: In their search for suspects in the ducks' decline, experts are also investigating the species' winter range south of the Canadian border. Alien shellfish such as zebra mussels are potential perpetrators. These creatures not only crowd out native species, but they also can store high levels of pollutants in their bodies. Diving ducks spend their winters feasting on shellfish, as this male surf scoter in California shows, and may be concentrating pollutants in their bodies as a result.
But studies in winter habitat suggest causes for concern. "First, lesser scaup tend to spend more time overwintering in inland waterways than greater scaup, which prefer estuaries," he says. "Contaminants can be more of a problem in estuaries, particularly where metals are concerned." Second, the researchers may simply have tested uncon-taminated ducks. "One thing our work in San Francisco Bay has revealed is that scaup and scoters use very circumscribed, localized areas during the winter," he says. "So if a group of scaup or scoters plops down in November in front of a refinery that's spewing selenium into the water, they will stay there all winter, gorging on contaminated shellfish."
Other studies show that mercury, selenium, cadmium, zinc and copper reduce carcass fat and pancreas size in San Francisco Bay diving ducks. "The contaminants also are linked to smaller body size in ducks," says Takekawa. "What this could mean is that ducks wintering in contaminated hot spots in the bay might be in poor condition when they reach their breeding grounds in the boreal forest. And that could reduce success in nesting."
Can we definitely link contaminants from the wintering grounds with breeding failures in the boreal forest? We aren't there yet, says Takekawa, "but what we have so far points that way."
As scientists move closer to solving the mystery of the disappearing ducks, the discovery of a smoking gun--a single, overriding reason for the decline--seems increasingly unlikely.
"It may well be that what we're looking at is a synergistic effect," muses Butterworth as he monitors ringnecks and scaup in a corner of the fast-changing boreal forest in Alberta, "multiple factors that magnify each other's effects to the detriment of the birds." He swats a mosquito gorging itself on his cheek.
"One thing's for sure," he says. "It's going to take a lot of work to nail it down."
Glen Martin, the environment reporter for the San Francisco Chronicle, braved the insects of northern Canada to report this story.