The Elepaio on Kauai, Oahu, and Hawaii are actually different species!  Although each was originally described as separate species more than 100 years ago, today they are currently treated as a single species, with subspecies on each island.  However, a research article published by Eric in 2007 showed that Elepaio do not respond as strongly to playbacks of Elepaio songs from other islands.  If Elepaio ever move from one island to another, this lack of song recognition could prevent them from interbreeding.  Furthermore, in 2009 Eric, Lindsay, and colleagues showed that Elepaio on each island are also genetically distinct, and that the Elepaio lineage first colonized Kauai about 2.3 million years ago.  Eric has submitted a petition to the American Ornithologists Union recommending that Elepaio on each island be officially recognized as distinct species.