Darren Naish: Tetrapod Zoology: No no no no NO: the Herring gull is NOT a ring species!
Discovering Darwin: Season 1 Episode 3: Chapter II - Variation Under Nature
SOLVED: Among arctic seagulls, hybridisation is possible between some species but not others. Heuglin's gull can hybridise with both the Black-backed gull and the Vega gull: The American herring gull can hybridise
Similar Species to Ring-billed Gull, All About Birds, Cornell Lab of Ornithology
Ring species - Wikipedia
Evidence for Evolution (Is there a Pattern of Change?) - ppt download
Wherefore and Whither the Ring Species?
Unit 4 Biology Chapters Evolution Biology Chapters Books On the Origin of the Species - by Charles Darwin On the Origin of the Species - - ppt download