Male Common Merganser
Credit: Herbert Clarke

Just after the long white carpet of ice that has frozen Maine's rivers since mid-winter finally breaks free, a fascinating phenomenon takes place. Smelt, a small river herring that migrate in schools and are caught by fishermen and women through the ice all winter on the rivers, make one last migratory surge.

It is at this time that the surfaces of rivers like the Kennebec and Penobscot in Maine are decorated with thousands of slivers of gleaming white that are the males of a large fish-eating duck called the Common Merganser. Both the males and females can be seen but the females have a more sublime coloration of grays and browns that makes them less visible to predators, especially later in the season when they will be trailed by a line of ducklings. Common Mergansers have a breeding range that extends from New Jersey north and west to Alaska and spottily south into the Rockies but more than 50% nest in the Boreal Forest of Canada and Alaska. They nest in Maine but most of the thousands feeding on smelt and other fish in Maine rivers in March and April are building up the energy for a flight hundreds if not thousands of miles north to the Boreal. Unlike many duck species, the Common Merganser nests in tree cavities often making use of old woodpecker nests or roost cavities which means that they require forests that have old trees in them.

Here's some video of Common Mergansers on the Kennebec River from March with Bald Eagles calling in the background: