A medium-sized prion. The dark “M” across the back is found in all the prion species, but is noticeably less pronounced on the Slender-billed Prion. Slender-billed Prion has a very pale face, prominent white eyebrow, and very narrow black tip to the upper tail. As suggested by its name, the Slender-billed Prion has the thinnest and least robust bill of the prion species. Breeds on islands in the southern Indian Ocean, the Falklands, and around subantarctic South America while ranging throughout southern oceans during the nonbreeding season. Very difficult to distinguish from other prion species at sea, but distinguishable with careful observation of all described features.