Diving-petrels are auk-like small petrels of the southern oceans. The resemblances with the auks are due to convergent evolution, since both families feed by pursuit diving, although some researchers have in the past suggested that the similarities are due to relatedness. Amongst the Procellariiformes the diving petrels are the family most adapted to life in the sea rather than flying over it, and are generally found closer inshore than other families in the order.
Diving-petrels are plankton feeders, taking mostly crustacean prey such as krill, copepods and the amphipod Themisto gaudichaudii, also taking small fish and squid. They have several adaptations for obtaining their prey incliude short powerful wings, a gular pouch for storing food, and their nostrils open upwards rather than forward pointing as it is in other tubenoses.
These birds nest in colonies on islands. One white egg is laid in a burrow in turf or soft soil. They are nocturnal at the breeding colonies. It has a long period of parental care (around 45 - 60 days) in the burrow, but once the chick fledges out to sea it is on its own.
Of the four species two, the Peruvian Diving-petrel and the Magellan Diving-petrel, have highly restricted ranges around South America's coasts, whilst the Common Diving-petrel and the South Georgia Diving-petrel range widely across the southern oceans, breeding on islands off New Zealand, sub-Antarctic islands in the Indian Ocean, and islands in the south Atlantic (like Tristan da Cunha).
Diving-petrels are amongst the world's most numerous birds, with Common and South Georgia Diving-petrels numbering several million pairs each. The Peruvian Diving-petrel, on the other hand, is threatened by guano extraction, introduced species and climate change, and is listed as an endangered species.
The four species are:
The evolution and systematics of these birds is not well researched. Several populations were described as distinct species and while most of them are only subspecies, some may indeed be distinct. The prehistoric fossil record was long limited to very fragmentary remains described as P. cymatotrypetes found in Early Pliocene deposits of Langebaanweg, South Africa; while this bird apparently was close to the Common Diving-petrel, no members of the genus are known from South African waters today.
In 2007, a humerus piece from New Zealand was described as P miokuaka. This was found in Early/Middle Miocene deposits and just as may be expected, it far more resembles diving-petrels than any other known bird, but presents a less apomorphic condition.