By Katherine Mehl
Sea ducks make up 42 percent of all North American duck species. They include eiders (common, spectacled, Steller's and king), scoters (black, surf and white-winged), mergansers (common, hooded and red-breasted) and goldeneyes (common and Barrow's goldeneyes), along with buffleheads, long-tailed ducks and the flamboyant harlequin ducks. With eider feathers of pastel greens and blues set among a deep jet-black background, or the fanciful headdress of the snappy-looking hooded merganser, sea ducks are some of the most ornately colored of all waterfowl.
As the name implies, sea ducks are adapted to life at sea. With most spending a considerable portion of the year along our coasts, the majority of these birds breed in northern areas such as the Canadian Arctic and Alaska. King eiders will even remain in frigid waters during the winter, staying as far north as the open water will allow. This is possible because they have special adaptations for life in cold environments, such as thick fluffy down with supreme insulation properties and unusual veins and arteries in their legs that warm the cool blood before it is returned to the body.
Sea ducks are well adapted for life at sea. For instance, their bills are highly specialized—from the heavy, stout bills of eiders, which feed on marine mussels, to the long, narrow, serrated bills of mergansers, which are used for catching and eating fish. As you might imagine, finding such food requires superb diving skills. Indeed, sea ducks are among the most accomplished divers of all waterfowl, with some reportedly diving to depths of 180 feet.
Perhaps the best way to understand how sea duck life history differs from that of other ducks is to contrast them with the familiar mallard. Of course, there is the obvious difference—mallards spend their winters on land and not at sea. Mallards typically breed during their first year. They also rely on seasonal wetlands, which may dry up during some years, and mallards are, therefore, well adapted to moving into new areas when habitat conditions change from one year to the next. Mallards generally breed each year and they lay fairly large clutches of nine to 12 eggs. Their nest success is low, but duckling survival is moderate, with mallards relying on multiple nests (renesting in the event of failed nesting attempts) each year to increase their chances of hatching ducklings. They typically live to be about 2 years old.
In contrast, sea ducks have delayed maturity, breeding for their first time at two to three years of age or even older. Sea ducks typically rely on stable environments with predictable food resources during the breeding season. Therefore, sea ducks most often return to the same area, year after year. From time to time, sea ducks will skip a year of breeding, especially when nesting in the Arctic, where snow and ice can delay the already short breeding season. Because of their more northerly ranges, sea ducks generally nest later than mallards. In contrast to mallards, sea ducks (with the exception of cavity nesters) generally lay smaller clutches of from four to six eggs. The chance for a sea duck to successfully hatch a nest may be greater, but unlike the mallard, they generally have only a single nesting attempt each year. Many sea ducks raise their young in open waters that lack aquatic vegetation, which leaves the ducklings in the open, vulnerable to avian predators. This means lower duckling survival rates than mallards. However, if a sea duck makes it to the adult stage, they typically live about seven years.
So, what do these differences mean for waterfowl managers? Because mallards breed every year, have larger clutches, frequently renest and have higher duckling survival, their populations can rapidly increase, as seen over the past decade. In contrast, sea ducks are adapted to stable environments, are slow to colonize new habitats, and produce fewer young per year. This means that relatively smaller portions of the populations can be harvested, and if their populations decline, they will be slower to recover.
This is important information. Eleven out of 15 species of sea ducks appear to have declining populations within some portion of their range (exceptions are common goldeneyes, buffleheads, red-breasted mergansers and common mergansers). Furthermore, two species (Steller's eider and spectacled eider) are listed as threatened. Thus, waterfowl managers need current, science-based models to establish sustainable harvest strategies for sea ducks, and they need it now.
The reasons for the apparent population declines are unknown. Researchers know little about the general ecology of most sea ducks and lack accurate population estimates. This is, in part, because sea duck breeding sites are often logistically difficult to reach and travel costs are high.
Today, sea duck populations face many challenges. For instance, common eiders and king eiders are still commercially harvested in Greenland. Also, there is the increasing risk of global climate change. Only with a strong understanding of species ecology and management will we be able to reverse these trends and continue to see these colorful ducks floating on the sea.