The Snowy plover

 The Snowy plover and the Kentish plover were once regarded as different varieties of the same species but now DNA evidence has shown that they are in fact two.
 

Western Snowy Plover - By  "Mike" Michael L. Baird - CC BY 2.0

 Dr Clemens  Küpper, from the University of Bath's Department of Biology & Biochemistry says, "Although they look similar, for them to have stayed as a single species they would have had to be able to breed with each other, but this wasn't possible because they were separated by thousands of miles of water!

For the first time we’ve shown that these birds have been separated for a long time and evolved in different directions.”  Read more