River Ducks Look Alike

     American goldeneye, bufflehead and common merganser ducks winter on rivers and larger impoundments through winter in southeastern Pennsylvania, as elsewhere.  The drakes of those species of ducks look alike, though their are minor traits that set them apart.  And the hens of these
 kinds of ducks also resemble each other.  These birds of different species are similar because they are adapted to a similar habitat. 
     Drakes are striking with dark plumages on top and white below and on their flanks so they are light like the sky above to predators deeper in the water, and dark on top to resemble the water to predators in the sky.  Males also have contrasting dark and white patterns, different in each species, on their upper parts to entice females of their respective kinds to mate.  Males of each type duck have their own pattern they share with their male kin because of their common genetic code.
     Females of each of these species have gray feathering on their bodies, but browner heads and necks.  They have subtle colors to be camouflaged, which is particularly beneficial to each species when the hens are incubating eggs and raising ducklings.  But they, too, have lighter feathering underneath. 
     Goldeneyes and buffleheads are related to each other, so one would expect them to look somewhat alike.  But mergansers are not related to either species, yet resemble both in several ways.  Species' habitats shape them so they will fit into and be successful in each kind's niche, including in the various forms of camouflage to be invisible when need be. 
     Goldeneyes and buffleheads slip under water to eat a variety of molluscs and crustaceans they shovel off the bottoms of rivers and larger impoundments.  But mergansers dive beneath the surface to catch small fish in their serrated, red beaks.  These species of ducks have different food sources to reduce competition among themselves in the same habitat.
     These river ducks are an example of how each habitat shapes its inhabitants to be somewhat similar in body form and coloring to live successfully in its niche.  Another example would be the streamlining of ocean-dwelling fish and whales.  Adapting to habitats is happening all the time.