Petrels of the genus Pterodroma are notorious for being difficult to identify at sea. Among the most problematic species are Cook’s (P. cooki), de Filippi’s (P. defilippiana) and Pycroft’s (P. pycrofti) petrels, the three most similar of those small Pterodroma united in the subgenus Cookilaria. P. defilippiana has also been called Defilippe’s Petrel (Roberson and Bailey 1991) or Masatierra Petrel (Harrison 1983, 1987). “Deflippe’s” is an anglicization of defilippiana, but as Giglioli and Salvadori (1869) named the bird for Professor F. de Filippi, the correct English spelling should be “de Filippi’s Petrel.”