Although Common Mergansers (Anseriformes: Anatidae: Mergus merganser) inhabit much of North America, their range shifts with the seasons. They overwinter across a wide swath of the United States, then spend their summers breeding in forests from the northern United States through Canada. They nest in cavities in large trees, and unlike many birds the parents do not feed their young. The tiny, flightless chicks tumble from their nests within a day of hatching and immediately start to hunt for insects on their own. Wherever they roam through life these diving ducks are usually found on lakes and rivers where they feed mostly on small fish, frogs, and invertebrates.
Adult males of this species have white bodies and dark green, iridescent heads. Females are colored quite differently, having bodies with more gray and crested rust-colored heads. Both sexes have long, serrated orange-red bills.
Populations of these large ducks have been relatively stable across North America for decades, but they have experienced a decline in some areas. Pollution from pesticides and heavy metals can reduce the abundance of their prey and adversely affect the development of their young. In spite of these threats they’ve managed to thrive across most of their range, at least for now.