Petrels are tube-nosed seabirds in the phylogenetic order Procellariiformes.
Petrels are a paraphyletic group of marine seabirds, sharing a characteristic of a nostril arrangement that results in the name "tubenoses".[1] Petrels include three of the four extant families within the Procellariiformes order, including the Procellariidae (fulmarine petrels, the gadfly petrels, the diving petrels, the prions, and the shearwaters), Hydrobatidae (Northern storm petrel), and the Oceanitidae (Austral storm petrel). The other Procellariiformes order are the albatross family, Diomedeidae.
The word petrel (first recorded in that spelling 1703) comes from earlier (ca. 1670) pitteral; the English explorer William Dampier wrote the bird was so called from its way of flying with its feet just skimming the surface of the water, recalling Saint Peter's walk on the sea of Galilee (Matthew xiv.28); if so, it likely was formed in English as a diminutive of Peter (< Old French: Peterelle (?) > Late Latin: Peterellus < Late Latin: Petrus < Greek, Ancient (to 1453);: Πέτρος|Petros < Greek, Ancient (to 1453);: πέτρα|petra = "stone").
All the members of the order are exclusively pelagic in distribution—returning to land only to breed.
The family Procellariidae is the main radiation of medium-sized true petrels, characterised by united nostrils with medium septum, and a long outer functional primary feather. It is dominant in the Southern Oceans, but not so in the Northern Hemisphere.
It includes a number of petrel groups, the relationships between which have finally been resolved to satisfaction.
The families Oceanitidae and Hydrobatidae are the storm petrels, small pelagic petrels with a fluttering flight which often follow ships.
The family Pelecanoididae is the four species of diving petrels, genus Pelacanoides. These are auk-like small petrels of the southern oceans.