Each week, the haunting wail of the common loon opens the Field Notes program. The loon’s cry always brings to my mind clear mountain lakes rimmed by lush coniferous forests, a handsome pair of birds in their formal black and white courting plumage calling across the quiet water.
Large lakes are necessary because this heavy-bodied, small-winged bird requires a long runway, skittering across the water’s surface to become airborne. Clean lakes are required because the loon hunts visually. And quiet waters are important because loons will abandon a nest if it's overly disturbed by people’s activities.
So imagine my surprise when, about this time one winter, I was relaxing on a warm beach on the Sea of Cortez in Baja California, and heard across the water that distinctive, plaintive cry. Loons: no doubt about it! There in the desert south, among cactus, warm saltwater, brown pelicans and blue-footed boobies were three common loons hanging out for the winter. Could they be from Montana? Possibly. We really have no idea exactly where Montana loons go in the winter. Common loons are recorded wintering along both the Atlantic and Pacific coasts, and as far south as Baja and the Gulf of Mexico. They will winter on nearly any large body of open water where there is an abundant food supply and little disturbance.
These loons had not a trace of their breeding plumage – they were in their vacation duds: informal brown. Wintering loons generally keep individual foraging territories during the day and congregate in loose groups, called “rafts,” at night.
Winter is not entirely easy for loons, though. In recent years, biologists have discovered massive die-offs of loons on winter beaches – especially the Gulf of Mexico. It seems that loons pick up mercury and lead in summer waters: mercury accumulated through the food chain from pollution, and lead from fishing sinkers. Over time, these toxins collect in the loon’s body, causing serious illness. But why large die-offs in winter? Well, the loon’s winter molt is an incredible energy drain when they must consume large amounts of food, and this stress increases the mortality of birds weakened by toxin poisoning.
To end on a positive note, though, loons are still around in Montana, especially because of the work of biologists and volunteers who put up buoys near nests each spring to reduce disturbance while the loons are incubating eggs. And now that “loony” wail makes me think not only of pristine Montana lakes, but where I’d like to spend my next winter vacation!
"Field Notes" is produced by the Montana Natural History Center.