Common merganser
Mergus merganser
L 18″ W 37″
Habitat: Common mergansers prefer cool, clear waters of northern boreal or western forests, although at times they have nested as far south as North Carolina and Mexico. Ponds associated with the upper portions of rivers in northern forested regions are often used (Johnsgard 1975). As with hooded mergansers, clear water is needed for foraging.
Nest: Although hollow trees are the usual location, ground nests under thick cover or in rock crevices are not uncommon. A wide variety of other locations have been reported such as chimneys, hawk nests, bridge supports, and old buildings. The species of tree used for nesting and the height of the cavity are apparently unimportant (Foreman 1976). Nest sites are usually close to water (Bellrose 1976) and are used repeatedly, probably by the same female (Palmer 1976). Artificial nest boxes have been accepted, especially in Europe. Preferred dimensions are 9.1 to 11 inches wide, and 33.5 to 39.4 inches high, with 4.7 × 4.7-inch entrances, 19.7 to 23.6 inches above the base of the nest box (Johnsgard 1975).
Food: Programs to reduce populations of this fish-eating merganser have increased trout and salmon production in several areas, at least temporarily. Generally, common mergansers are opportunistic feeders with salmon taken extensively in some areas and suckers, chubs, and eels in others. In warm-water areas, food is usually rough and forage fish such as carp, suckers, gizzard shad, perch, and catfish. In some areas, water plants, salamanders, insects, or molluscs may be important in the diet of this species (Palmer 1976).