Why have Alaska's dabbling duck populations increased? One thing we know is the state has gotten warmer. Between 1949 and 2007, the state's average temperature increased by 3.4 degrees Fahrenheit. Temperature increases were largest in winter and spring and were similar throughout the state. But the trend toward a warmer climate has not been linear. In 1976, Alaska underwent a dramatic change in climate that produced much warmer temperatures compared to the previous 25 years. These higher temperatures have persisted over the past 30 years. This abrupt warming coincided with a shift in the phase of the Pacific Decadal Oscillation (PDO). The PDO is a long-lived El Niño-like pattern of Pacific climate variability. Cool PDO phases prevailed from 1890-1924 and again from 1947-1976. Warm PDO phases prevailed from 1925-1946 and from 1977 through at least the mid-1990s.
A look at changes in Alaska's dabbling duck populations suggests the increases were larger after the mid-1970s when the state began experiencing warmer springs. Whether this abrupt climate change is responsible for the increase in duck numbers is unknown, but it's certainly possible that an earlier spring has benefited some species by increasing their reproductive success.
While Alaska's waterfowl may benefit from a warming climate (at least in the short term), there may be negative long-term consequences as well. Researchers at the University of Alaska-Fairbanks recently looked at changes in wetland numbers and water area in Alaska's interior between 1950 and 2002. All areas lost wetlands during this period, with some places losing as much as 25 percent of total surface water. A leading cause of these losses could be melting permafrost. When the permafrost layer under these wetlands melts, water drains into the soil rather than pooling on the surface. Another potential cause could be increased evapotranspiration in wetlands during warmer and longer growing seasons. In both cases, the same temperature increases that may have led to larger duck populations may also be leading to less duck habitat.
So far our discussion of Alaska's waterfowl has been limited to duck species counted in the TSA. Of the 15 species of sea ducks that occur in North America, only three are included in the TSA. All the continent's sea duck species breed and winter in Alaska. Four species of eiders (common, king, spectacled, and Steller's) and three species of scoter (black, surf, and white-winged) occur year-round in the state. Unfortunately, many populations of eiders and scoters appear to have declined, including some in Alaska.
While some king eiders breed in the Arctic coastal plain, Alaska sees most of these birds in winter. Continentally, king eiders winter in two distinct populations: one in the Atlantic and one in the Pacific. The entire Pacific population winters in the Bering Sea, mostly along the Alaska Peninsula and Aleutian Islands. During spring, these birds migrate within sight of Point Barrow on their way to breeding grounds in the Canadian Arctic. More than 100,000 of the birds have been counted in a 30-minute period. Roughly 300,000-400,000 king eiders have passed by Point Barrow in recent years, down from 600,000 birds in the 1970s. Unfortunately, reasons for the decline are unknown.
In North America, breeding populations of spectacled and Steller's eiders occur exclusively on Alaska's Arctic coastal plain and Y-K Delta. Both species are listed as threatened under the Endangered Species Act. Breeding populations of spectacled eiders declined by more than 90 percent on the Y-K Delta from the 1970s to the early 1990s, but their numbers now appear stable. In contrast, Steller's eiders have virtually disappeared from the Y-K Delta, and the birds are now largely confined to the Arctic coastal plain. Steller's eiders winter along the Alaska Peninsula and Aleutian Islands. The wintering location of spectacled eiders remained a mystery until 1995, when birds fitted with satellite transmitters finally led biologists to their wintering grounds in the middle of the Bering Sea.
Although Alaska now supports a growing share of the continent's breeding ducks, the state is perhaps best known for its geese. Waterfowl managers recognize 28 goose populations in North America, a quarter of which breed mostly or only in Alaska. The state supports all of the world's tule and Pacific white-fronted geese and 90 percent of all emperor geese. Dusky Canada geese and three subspecies of cackling geese also breed exclusively in Alaska. And 80 percent of the world's Pacific brant breed on the Y-K Delta and Arctic coastal plain.
Continue Reading >>