Why has the scaup population – a once common type of diving duck – plummeted over the past two decades? Alarming new research indicates that the waterfowl are poisoned as they feed along the lower Great Lakes
By Megan Ogilvie
The small, twin-engine aircraft banks left, cheap making a long, slow turn. Framed by the window, the Lake Erie shoreline comes into view to reveal a collage of colour – cobalt blue, taupe and beer bottle green – below. It’s a sunny day in early autumn; flecks of red and yellow and orange have started to appear in the forests and fields and a nip is in the air. Scott Petrie, research director of The Long Point Waterfowl and Wetlands
Research Fund (LPWWRF), is looking out of the window, watching for great flocks of waterfowl. From the rumbling aircraft Petrie estimates the numbers of all sorts of waterfowl, from scoters to buffleheads, long-tailed ducks to teal. But two species of duck hold special interest: greater and lesser scaup, whose population numbers have been dropping for nearly half a century.
Greater and lesser scaup are closely related diving ducks, and the two lookalike species are often grouped together and commonly referred to as “scaup.” Males of both species are black and white and grey and have striking yellow eyes. The drabber females are a dark, mottled brown. Greater scaup, as their name suggests, are larger than lesser scaup and have a broader, rounder head. Lesser scaup make up about 85 percent of the continental scaup population and breed exclusively in North America, while their slightly larger relative is also found across Eurasia. On this continent, scaup primarily breed on the prairies and in the boreal forests of Canada and Alaska, and winter in the southern United States and Mexico. Due to their vast range, scaup have several migration routes. Thousands of the birds travel through the Mississippi valley, others along the Atlantic coast and many through the Great Lakes region. Each year, during spring and fall migrations, tens of thousands of scaup stop to rest and feed for several weeks on the lower Great Lakes.
There are between 3.4 and 3.5 million scaup in North America, according to recent estimates. This is the lowest number ever recorded for scaup since the Waterfowl Breeding Population and Habitat Survey, an annual evaluation of the spring population size of certain North American duck species, began in 1955. Ornithologists first noticed a decline in the continental scaup population in the 1970s. Over the next two decades, scaup numbers continued to drop – precipitously. But experts weren’t worried. Other waterfowl populations were falling, primarily due to drought conditions on the prairies, which are prime breeding grounds for many of these species. But as water conditions on the prairies improved, so too did waterfowl populations. Except for scaup. “Their population has continued to decline every year, even at a time when most other waterfowl species are returning,” says Petrie. “The scaup population is not coming back.”
SCAUP POPULATIONS have dropped from about 6.3 million in the mid 1980s to about 3.5 million now. Waterfowl scientists across North America are trying to determine what caused the decline in the population and what is impeding its recovery. Christine Custer, a wildlife biologist with the U.S. Department of the Interior who studied scaup in the late 1990s, worries that a plummeting scaup population is indicative of other problems in an ecosystem. “Scaup could be the canary in the coal mine,” she says. “Something is going on somewhere. If their population is having problems, it could mean bigger ramifications for other animal and plant species.”
Waterfowl scientists are investigating three main hypotheses for falling scaup populations. One theory is that human-induced climate change is altering the ecosystem at breeding grounds for scaup in the north. Researchers are also studying whether food limitations – snails are one of the birds’ primary food sources – in the upper midwest prairies are affecting scaup survival. Here in Ontario, Petrie and his colleague Shannon Badzinski, also with LPWWRF, which is run out of Bird Studies Canada in Port Rowan, are investigating how environmental contaminants, acquired when the birds stop to rest and feed on the Great Lakes, affect scaup reproduction or survival.
According to Petrie, scaup are in danger of being poisoned by a new food source – zebra mussels. The non-native species of mollusc was accidentally introduced to the Great Lakes in the mid-1980s and has since multiplied, spreading to all the Great Lakes, choking out other lake life and dramatically changing aquatic ecosystems. As zebra mussels began to cover the rocky bottoms of the Great Lakes, more and more scaup started to spend longer periods of time on their staging g rounds on Lake Ontario and Lake Erie. Scaup numbers at Long Point on Lake Erie jumped from an average of about 7,500 birds during the 1970s and 1980s to nearly 50,000 in the 1990s. Quickly adapting to the new, abundant food, scaup switched to a diet dominated by zebra mussels, eating less of their traditional foods, such as native gastropods and aquatic plants. LPWWRF studies confirmed that scaup now eat large quantities of zebra mussels on the lower Great Lakes in the spring. But this novel food was no blessing, says Petrie. Zebra mussels, which feed by filtering phytoplankton from the water column, accumulate contaminants from the water much faster than do native mollusc species, which feed on algae growing on rocks. The mussels, in turn, pass the contaminants on to their predators, including scaup.
One such contaminant is selenium, a semi-metallic element birds require in trace amounts but that is toxic at high doses. Selenium occurs naturally in rocks and soils. In the Great Lakes region, however, soils are deficient in the mineral and it is believed that the element gets into the Great Lakes as an industry byproduct, primarily from the burning of fossil fuels. Preliminary research has shown that selenium is the only contaminant present in high enough amounts to damage the health of the scaup that spend time on the Great Lakes.
Christine and Thomas Custer of the U.S. Geological Survey published a paper in 2000 revealing that selenium concentrations in scaup collected in Lakes Erie, Michigan and St. Clair in the early 1990s were high enough to be considered toxic. “This paper really got this theory going,” says Petrie. “Prior to their research, nobody knew that selenium was a potential problem for scaup.” Petrie decided to expand the Custers’ work, whose study looked at scaup in heavily industrialized areas, a worst-case scenario for waterfowl. Was selenium contamination in zebra mussels widespread? Were scaup acquiring potentially harmful burdens of selenium from zebra mussels in other, less industrialized, areas of the Great Lakes?
WATERFOWL SCIENTISTS have recently noticed a slight dip in other diving duck populations. North American populations of diving species, such as canvasbacks, buffleheads and common goldeneyes, are not tumbling but are lower than expected. Scaup could be a sentinel species, their sharp population decline illuminating an ominous trend for other wildlife species. Rod Brook, a waterfowl population specialist with the Ministry of Natural Resources in Peterborough, says scaup could be an important indicator species. Waterfowl, he says, are one of the best surveyed birds in North America: “There’s a concern for other boreal species that we don’t monitor as closely as scaup.”
LPWWRF studies have shown that at least 77 percent of lesser scaup and 94 percent of greater scaup in the lower Great Lakes left spring staging areas with potentially unhealthy burdens of selenium. The research is clear: scaup are acquiring selenium after they arrive at the lower Great Lakes in the spring and begin eating hundreds of zebra mussels. Once they have eaten their fill, the birds fly to their breeding grounds. Female lesser scaup may pass the selenium to their eggs by a process called depuration. Waterfowl scientists, including Petrie, predict that selenium burdens in eggs might be lowering the number of chicks hatched in the northern breeding grounds.
That is why LPWWRF researchers are satellite tracking female lesser scaup as they leave Long Point Bay on Lake Erie and Lake Ontario’s Hamilton Harbour. Petrie and Badzinski hope to determine the amount of time lesser scaup stay at spring and fall staging areas on the lower Great Lakes and to identify subsequent staging areas, as well as breeding grounds and wintering areas the birds use after leaving the Great Lakes. Knowing the amount of time female lesser scaup take to fly to their breeding grounds and how long they take to lay eggs will allow researchers to estimate how much selenium these birds are passing on to their unborn chicks. Selenium has a 19-day half-life, which means that one half of a set amount of the element takes 19 days to disintegrate. Petrie says this is a key piece of information. As soon as scaup stop eating contaminated zebra mussels, the birds start to depurate selenium, he explains. “So, if a female starts to lay eggs 19 days after she leaves the Great Lakes, only half as much selenium can be deposited into the eggs.”
The LPWWRF Scaup Tracker program was launched in spring 2005 when satellite tracking devices, used to show birds’ exact migration routes, were implanted in five female lesser scaup. After spending several weeks in May feeding around Long Point, in Lake Erie, the five scaup flew north and west to their breeding areas. By June, the females were scattered from the south coast of Hudson Bay to the Yukon.
In spring 2006, LPWWRF researchers trapped 20 scaup, 15 females and five males from Long Point and Hamilton Harbour. The birds were taken to the Avian Energetics Laboratory at Bird Studies Canada, where a satellite transmitter was implanted into each bird. This is a costly affair: A single transmitter costs $3,000 and the entire process costs $5,000 per bird. For the next two years, Petrie and Badzinski plan to track the scaups’ movements at their breeding grounds, at their over wintering sites and during migration.
Until last year, Petrie’s research focused on lesser scaup, but the population of greater scaup may also be declining. Lindsay Ware, a master’s student at the University of Western Ontario, has begun to investigate whether unhealthy burdens of contaminants affect the overall health of greater scaup. She has made Lake Ontario’s Hamilton Harbour her research spot.
Hamilton Harbour, a 2,000-hectare embayment separated from Lake Ontario by a long, sloping sandbar, is bounded by highways, industry and urban waterfronts. Steel plants loom over the southern shore, rock and rubble form unnatural beaches and piers poke like long tongues into the murky bay. Scaup, like many waterfowl, use Hamilton Harbour as a staging ground during both their spring and fall migrations. But some greater scaup are now opting to winter in the harbour, where warmer lake waters do not freeze over and an abundance of zebra mussels provides a year-round smorgasbord for the birds. “The bottom of boats, the sides of piers, the pillars on docks, they’re all covered in zebra mussels,” says Ware, describing parts of Hamilton Harbour. “Even rocks at the bottom of the lake are completely caked with them.”
Since scaup are difficult to raise in a laboratory environment, Petrie and Ware rely on lab studies conducted on mallard ducks to show how selenium affects scaup. Research has revealed that selenium levels above 10 micrograms per gram are harmful to reproduction in mallards, and selenium levels above 33 micrograms per gram are harmful to the ducks’ general health. All of the greater scaup Ware caught and analyzed in 2006 had selenium levels between 10 and 50 micrograms per gram – high enough to cause both reproductive and overall health problems.
This year, LPWWRF researchers will implant satellite tracking devices in 10 greater scaup to find out this species’ migration patterns. Each of these experiments brings Petrie and his researchers one step closer to understanding why scaup populations continue to drop. If waterfowl scientists could definitively show that elevated selenium levels are affecting scaup health and reproduction, this evidence may be enough to initiate a clean-up of the lower Great Lakes of selenium. “We’re not going to get rid of zebra mussels,” Petrie laughs. “But we could reduce the amount of selenium getting into the Great Lakes by regulating industry in the region.” Doing that could help scaup, as well as a number of yet unknown species, bounce back to traditional population numbers. “This theory won’t be the one silver bullet to solve scaup population decline,” says Petrie. But, he suggests, it may prove to be a final piece in a yet unsolved puzzle.
Megan Ogilvie is a health reporter at the Toronto Star and an avid birder.