Summer Range: Common Mergansers arrive on their breeding grounds shortly after ice cover has melted off the lakes in late winter or early spring. In North America, their breeding range spans the continent from New York through the upper Great Lakes, the Rockies and California, extending north to the timberline in Canada and Alaska.
Winter Range: Common Mergansers are extremely late migrants, remaining on their northern range until ice forms on the lakes, and seldom moving until mid-November. The birds spend winters from southern Canada to North Carolina, Kentucky, Arkansas and northern Mexico, and farther north along the coasts. Many mergansers fly south only as far as they must to find large bodies of open water.