Empidonax Flycatchers

     Empidonax flycatchers are a genus of small birds in the flycatcher family that fascinate me because they demonstrate well a divergence of several species from a single species.  Flycatchers are a family of birds that catch flying insects in mid-air and nest in North America, but winter in Central and South America where flying insects are available year around.   
     There are five kinds of flycatchers in the Empidonax genus, and they are all nearly identical in appearance, making them almost impossible to identify, except by song and nesting habitats.  They are all four and a half to four and three quarters inches long and olive-gray.  Each kind has two white wing bars on each wing and a white ring around each eye.  All species jerk their tails up and down when perched on twigs.  The songs of the males of all species are short, simple and somewhat similar.  And their nests, that hang below forks of twigs, are built similarly.  With all those characteristics in common, one would have to think these five types of flycatchers had a common ancestor in the recent past. 
     By exploiting five different habitats in North America for nesting sites and food, the original species diverged into five.  Those five kinds of flycatchers don't have to compete for nesting sites or food because there is one type per niche.
     Though the original Empidonax species diverged into five, all its descendants kept the camouflaged plumage of the original, which blends and hides them among leafy trees and shrubbery to escape the notice of predators.  But the simple song of each kind became a bit different than its close relatives because of geographic isolation, allowing the genders of each species to find each other among their relatives on migration and where habitats overlap.        
     Acadian flycatchers raise young along streams in deciduous floodplain woods in the southeastern United States north to  the latitude of Pennsylvania.  Their cradles often are on twigs that hang over the water of woodland streams.  Males' songs are a sneezed "pete-sa". 
     Least flycatchers nest among scrub trees and woods margins across Canada and in northern New England.  There song is a quick, dry "cha-beck".
     Willow flycatchers rear offspring in dry thickets, including in large patches of multiflora rose bushes, across much of the United States.  Male of this species sing a nasal, scratchy "fitz-bu".
     Alder flycatchers hatch youngsters in alder bush swamps across southern Canada and the northern United States.  Males sing "fee-bee-o".
     And yellow-bellied flycatchers nest in spruce-fir forests across Canada and in northern New England.  Males of this species sing a whistled, ascending "per-wee" or a dull "che-bunk".  This species also has yellow underparts, as their name implies.
     Notice that all songs of these little birds are simple and almost all of them have two syllables, again showing their close relationship.  They probably only recently diverged from a common ancestor to exploit different niches, thus spreading the original kind into other habitats, which might allow it longer life as a genus.  If one or two branches of the original species dies out, perhaps other branches will continue to live. 
     Many families of animals spread into different niches, thus not "putting all their eggs in one basket" if disaster strikes.  By one species spreading into different niches and becoming several kinds, the original species may prolong its tenure on Earth.