The genus Procellaria traditionally consists of four species, two restricted to New Zealand and two widespread in the Southern Ocean. All four are threatened because of incidental mortality on longlines and other fishing gear. The White-chinned Petrel P. aequinoctialis is the seabird killed in largest numbers by fisheries in the Southern Ocean. A spectacled form recently has been elevated to species status, Spectacled Petrel P. conspicillata, based on differences in morphometrics, vocalisations and breeding phenology. Cytochrome b sequences support species status for the Spectacled Petrel and show that the White-chinned Petrel has two regional populations, one around New Zealand and one throughout the South Atlantic and Indian Oceans. White-chinned and Spectacled Petrels segregated approximately 0.90 million years ago by allopatric fragmentation, and the two populations within White-chinned Petrels diverged approximately 0.35 million years ago. Climate changes and corresponding changes in ocean currents are most likely responsible for these patterns.