Small but rather stocky and stout-billed petrel of subtropical eastern Pacific and Humboldt Current; not seen from mainland. One of several similar species, Masatierra is best identified by gray head and collar at sides of neck, rather stout bill, and plain grayish tail without a black tip. Much smaller than Juan Fernandez Petrel with quick wheeling flight unlike more easy and less hurried-looking flight of Juan. Also compare with Stejneger’s and Cook’s Petrels.