One of the benefits of living next to the Bitterroot River is the near constant presence of Common Mergansers has they float on past. Dressed in stately garb, the male is strikingly black and white with a bright red bill, whereas the hen possesses a russet head adorned with a ragged crest of feathers. These outfits make the moniker of Common unbefitting such eloquence.
Common Mergansers spend the majority of their time cruising the riffles of our rivers where they seek a variety of fish, usually the slower species (easier to catch). Occasionally they will haul out onto a mid-stream rock for a loafing session. These rocks are normally coated white with layer of merganser excrement. The merganser’s morphology is uniquely fitted to the pursuit of fish. Fine serrations line each side of the mandibles, and the body is hydrodynamical, torpedeo-shaped with huge, propelling feet placed at the rear of the body. The body design has a lot in common with our submarines.
Common Mergansers are secondary cavity nesters, meaning that they nest primarily in the abandoned nest cavities of Northern Flicker and Pileated Woodpeckers. These two woodpeckers inhabit the cottonwood forests that line the rivers, and they are large enough to create appropriately sized nests that are suited to the Common Merganser’s needs. Once in the nest, they lay anywhere from 6 to 17 eggs! This explains the large family groups that crowd the eddies by mid-summer. Young are fishing on their own immediately upon leaving the nest, although insects are the right-sized prey for the first weeks of life.
Common Mergansers enjoy distribution across the entire Northern Hemisphere, and they are known by many names with each locale and language. In the UK, they are the goosander, a name that I particularly relish. Goosander is name of unknown origin, but it appears that it came into use around 1766 in Britain. It has a certain poetic flair to it, though.
Some greedy fishermen claim that Common Mergansers are detrimental of game fisheries. This position is largely unsubstantiated with studies showing that Common Merganser do occasionally consume game fish (between 10% and 20% of their total diet), but the research also shows that non-game or rough fish represent the vast majority of the diet. Think about it, would you waste your time chasing the fastest fish or the slowest? Timken and Anderson (1969) is the best Common Merganser food habit study that I was able to find.
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