The Prions are small petrels in the genera Pachyptila and Halobaena. They form one of the four groups within the Procellariidae (also referred to as the prions), along with the gadfly petrels, shearwaters and fulmarine petrels. They're found in the Southern Ocean and breed on a number of subantarctic islands. Prions grow long, and have blue-grey upper parts and white underparts. Three species of prion have flattened bills with a fringe of lamellae that act as strainers for zooplankton. All pri… (More on Pachyptila)