The rockhopper penguins are three closely related taxa of crested penguins that have been traditionally treated as a single species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 and are sometimes split into two or three species. Not all experts agree on the classification of these penguins. Some consider all three as distinct species, some split the Western and Eastern forms into the Southern Rockhopper Penguin and keeping the Northern Rockhopper as distinct, while other experts lump all 3 calling it simply Rockhopper Penguin. The subspecies in the group are:

• Western Rockhopper Penguin, Eudyptes (chrysocome) chrysocome
• Eastern Rockhopper Penguin
  Eastern Rockhopper Penguin
  The Eastern Rockhopper Penguin although genetically differnt is still often considered as a subspecies of the Southern Rockhopper Penguin.-Distribution:...
  
  , Eudyptes (chrysocome) filholi
• Northern Rockhopper Penguin
  Northern Rockhopper Penguin
  The Northern Rockhopper Penguin, Eudyptes c. moseleyi, is usually considered a subspecies of rockhopper penguin, although fairly recent studies show evidence of distinction from the Southern Rockhopper Penguin group Eudyptes c. chrysocome/E. c. filholi.A study published in 2009 showed that the...
  
  , Eudyptes (chrysocome) moseleyi