Wintering River Ducks

     It is interesting and amazing to me how similar three kinds of ducks that winter on rivers and lakes in the Mid-Atlantic States are.  But not a surprise because American goldeneyes, buffleheads and common mergansers share (converge) on the same summer and winter habitats.  And goldeneyes and buffleheads are relatives in the same genus of ducks, but diverged a bit from a common ancestor.
     These three kinds of wintering ducks in southeastern Pennsylvania, as elsewhere, have many characteristics in common.  Drakes of these species have similar, striking dark and white colors and color patterns, mostly dark on top and white below.  The related and beautiful goldeneye and bufflehead drakes have almost identical color patterns.  However, male common mergansers are particularly handsome with iridescently green heads and blood-red beaks.  Hens of all three types are mostly brown, which camouflages them, including when they are raising ducklings.
     But these duck species have many more similarities.  They all nest by lakes and rivers in forests of Alaska and Canada, but not in the same places, though there is overlap.  Buffleheads raise young in southern Alaska and western Canada.  Goldeneyes hatch offspring in Alaska and across the middle of Canada from coast to coast.  And the mergansers rear ducklings across southern Alaska and southern Canada.
     Females of all three of these duck species hatch ducklings in tree cavities in northern woods, hollows created by woodpeckers and wind ripping limbs off trees, which exposes the inner wood to agents of decay.  Buffleheads, being small ducks, nest in abandoned flicker holes and similarly-sized tree hollows.  (Flickers are medium-sized woodpeckers.)  Goldeneyes hatch young in cavities that are larger than the ones buffleheads use, which reduces competition for nesting sites.  The mergansers lay eggs in still larger tree hollows.  Each species squeezes into as small an opening as it can to eliminate at least some predators.  The ducklings of each kind feed mostly on insects, which gives them much protein for growth.  However, when merganser young are a couple weeks old, they turn to eating small fish.    
     Buffleheads, American goldeneyes and common mergansers all winter on larger, open, inland waters, including fresh water rivers, lakes, and ponds in the case of the buffleheads.  They winter far enough south in the Lower 48 to be able to find open water to get their food. 
     Wintering buffleheads and goldeneyes dive gracefully under water to feed mostly on small crustaceans, mollusks, including snails, and insect larvae among stones on the bottoms of lakes and rivers.  Mergansers, however, slip under water to catch and ingest small fish during winter, as they do the rest of the year.  The different diet of the mergansers eliminates rivalry for food with buffleheads and goldeneyes, which allows all three species to be able to co-exist in the same habitats, summer and winter. 
     These striking, intriguing duck species that winter in southeastern Pennsylvania, and through much of the United States, wherever there is open water, have many characteristics and life styles in common because of their sharing summering and wintering habitats and niches.  And yet the precise niches of each kind allows it to live with reduced competition with the other species.  These ducks, like all forms of life, are truly remarkable in beauties and intrigues.