Monday, March 7, 2011

BIG BLACK BIRDS WITH BULGY BEAKS


These are the scoters, three species of ducks we are fortunate to see in the Pacific Northwest every winter. The males are black with bright head markings, the females mostly dark brown. They breed in Canada and Alaska and winter along most of the temperate coasts of the United States. They are mostly confined to salt water in the nonbreeding season, although wintering numbers on the Great Lakes have increased because of the proliferation of zebra mussels there.

The Surf Scoter (Melanitta perspicillata) is the most common of the three scoters wintering in the Pacific Northwest. While all three scoters include a variety of marine invertebrates in their diets, they seem to be bivalve specialists. The heavy bill of a Surf Scoter provides it with strength to pull mussels loose from their attachments to rocks and pilings. Accordingly, Surf Scoters are common where there are large beds of mussels, and that includes a lot of territory in this region.

Surf Scoter courtship displays are fun to watch. The male flies a short distance with loudly whistling wings, then slides to a stop on the water with both wings raised high. How could a female not be impressed? Like other ducks, they pair during the winter and fly back to the breeding grounds together. Most males probably don’t breed until they are two years old, and younger males can be distinguished in winter by less brightly colored bill and often smaller white head patches.

White-winged Scoters (Melanitta fusca) appear to be more locally distributed than their Surf cousins. They are most common in bays with sand substrates, where clams are much more common than mussels, surely indicating a food preference. The White-winged is a bit bigger than the Surf and is our largest duck. The big white wing patches are prominent in flight but may be hidden on a resting bird. Note the difference in feathering on the bill of the two species, useful when identifying juveniles, which look very similar.

The Black Scoter (Melanitta americana) is the least common and most locally distributed of the PNW scoters. Its head shape is more like that of other ducks, presumably indicating it is less extremely adapted for bivalve pulling. As in the Surf Scoter, the male wings whistle in flight.

Male scoters see their mates on a nest on the breeding lake and then head for the coast in what is called molt migration. Female Surf Scoters follow the males after they raise their young, but female White-wings undergo this molt on the breeding grounds. The molt migrants arrive at their destination and begin their body and wing molts. They are flightless during wing molt, so they need to be somewhere with abundant food resources for that period. After completing molt, many continue farther south along the coast.

Scoter migration is dramatic on the outer coast, where flock after flock of Surf Scoters pass by just offshore, heading south in September and October and north in April and May.  Smaller flocks of White-winged Scoters are interspersed, but you’ll have to look long and hard for the much smaller numbers of Black Scoters. Migrants of many other seabirds, in flocks and by themselves, add to the thrilling experience of a few hours spent on an outer-coast point.

Dennis Paulson

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