A Pair of Ducks?

     While driving through Lancaster County, Pennsylvania farmland this March to experience what was currently happening in nature, I noticed a small group of ducks in a "hole" of deeper, slow water in a cow pasture stream.  With 16 power binoculars, I scanned that gathering of ducks and saw they were a handsome pair of mallards, three beautiful wood ducks, two of them drakes and one attractive male hooded merganser, for a total of six ducks of three species.  The mallard pair may have been there to hatch ducklings under shrubbery along the stream, but the other ducks were surely migrants that will raise young elsewhere.  At any rate, I was struck with that seemingly odd combination of species, in such a small waterway in the wide, open spaces of a meadow with only a few young trees along the stream. 
     Wood ducks and hooded mergansers are shy species that generally stay under cover and nest in tree cavities and nest boxes erected for them near waterways, ponds and swamps in woodlands.  However, some, more adaptable, wood ducks in farmland are hatching offspring in tree hollows and nest boxes in meadows that have at least some trees.     
     While watching those lovely ducks in that little, running stream for a few minutes, I noticed the hen wood duck seemed attached to the male hooded merganser, or the drake merganser was attached to the female wood duck, as if they were a mated pair.  She stayed close to him, or the other way around, the whole time I was there.  
     Woodies and hoodies have diverged in what they eat, which allows them to occupy the same habitats.  Wood ducks mostly ingest aquatic invertebrates, water plants, and seeds and small nuts and hooded mergansers consume aquatic invertebrates, crayfish, tadpoles and small fish they dive under water to get.  But these duck species have converged in other ways, including habitat choices in the northeastern United States and nesting places in those shared habitats, which pushes them into competition with each other for hollows to hatch ducklings.
     With rivalry for nesting cavities, and more female ducks of two kinds than nesting holes available, some female woodies and hoodies that couldn't find a nesting hollow and desperate to lay the eggs forming in them, place their eggs, one at a time, in clutches in hollows while the clutch owners are away from their nesting cavities.  Like most birds, except hawks, eagles and owls, ducks lay one egg a day and don't brood them until all eggs are laid so the young all hatch on the same day.  Therefore, the clutches are available to interloping female ducks.
     Therefore, some broods of wood duck hens and hooded merganser females have some ducklings of each species in them.  Each hen escorts and broods the ducklings that she hatched until they are old enough to take care of themselves.  The younger ducklings of both species eat lots of invertebrates, which gives them much protein for growth.  But as they get older, each species ingests the foods of its elders.
     Some ducklings from mixed broods might imprint on the species of the female that raised them, therefore some adult woodies and hoodies may get attracted to the opposite gender of the other species.  It could have been that the drake hooded merganser was attracted to the female wood duck as she was migrating north with others of her kind.  But all this is speculation.  Perhaps the woody and hoody were not paired, but I never saw anything like that among birds before.  This is one of the happenings that makes observing nature so interesting and enjoyable.  There is always something new and intriguing going on and it is all beautiful and inspiring.