In North America,many Kinds of Birds Have Closely Related Eastern

Essay

In North America,many kinds of birds have closely related eastern and western counterparts species or subspecies)that sometimes produce hybrid offspring where their ranges overlap.For example,Baltimore and Bullock's orioles have been known to produce hybrid offspring in Nebraska,as do yellow- shafted and
red- shafted flickers.Formulate a hypothesis to explain this widespread pattern of closely related eastern and western birds.