Cavity-nesting Ducks in Eastern North America

     Females of five kinds of ducks, including wood ducks, hooded mergansers, common mergansers, American goldeneyes and buffleheads, hatch ducklings in tree hollows and nest boxes in eastern North America.  Those cavities offer protection to the setting mothers and their eggs and young from weather, flooding and some predators, hazards that would harm them on the ground.  When the young hatch, they use their toe nails to climb up the inside walls of their cradles and jump out the entrance to the water, or ground, sometimes a bit of a distance from water.  In that case, each mother leads her brood to water to feed and, hopefully, live long enough to grow up. 
     All these types of ducks are small and slender, which enables them to clamber about in the trees.  Males of all these species are striking in appearance, real dandies to portray good health and vigor to prospective mates, and drive away other males of each drake's kind.  The females of each species, however, are plain and brownish, which camouflages them while raising young.  Females of many bird species are more valuable than males to nature because they lay eggs and rear offspring.  Therefore, they are better protected by blending in.  Field guides to birds show the plumage colors and patterns of these birds.  
     Although all these duck species migrate through southeastern Pennsylvania, only wood ducks commonly nest here, in tree cavities and nest boxes along streams in woodlands, swampy woods where tree limbs hang over still water, and recently in strips of trees along waterways in farmland, wherever boxes have been erected.  They arrive here in March already paired.  And during that month, female woodies search for vacant cavities they can use for nesting, accompanied by their mates.  By early April they begin laying eggs, one a day, in their nursery until they have a clutch of about 15 eggs.  The ducklings hatch toward the end of May.  They eat a variety of invertebrates while their parents consume vegetation, reducing rivalry for food between them.  Ducklings need protein they get from invertebrates for rapid growth.
     Hooded mergansers nest in much the same habitats in the eastern United States as woodies, but very sparingly in southeastern Pennsylvania.  Both genders have crests they can raise and lower.  This type of duck eats crayfish, small fish and other aquatic creatures, thus reducing competition for food with wood ducks.    
     Related to hooded mergansers, common mergansers hatch ducklings in tree cavities farther north than their relatives, mainly across Canada.  They, too, eat small fish, but in larger bodies of water than hooded mergansers do, reducing rivalry for space and food with their smaller relatives.
     Common goldeneyes and buffleheads are related to each other.  Drakes of both species have similar plumage patterns, demonstrating their common ancestry.  Both these kinds of ducks hatch young in tree cavities in the northern, lake-riddled forests of Canada.  But because goldeneyes are a little bigger than buffleheads, they lay eggs in larger hollows than their relatives.  Goldeneyes use hollows chiseled out by crow-sized pileated woodpeckers, then deserted.  Buffleheads, however, lay eggs in holes chipped out by the jay-sized northern flickers, then abandoned by those woodpeckers.  These duck species using different sized cavities reduces competition for nesting sites between them.
     Though only the woodies are common breeders here, we southeastern Pennsylvanians can enjoy all these handsome duck species when they migrate through in spring.  Many common mergansers, common goldeneyes and buffleheads winter here as well, mostly on the Susquehanna and Delaware Rivers and larger, built impoundments.  But even if we don't see them, it's nice to know they are in this area at least part of each year.