A small, fast-flying petrel with long narrow wings and bright white underparts. Found singly or in loose aggregations, well offshore in warmer Pacific waters, mainly from March to August. Flight varies from low and weaving, into the wind, to high and arcing across the wind. Note gray cap and upperparts with dark M pattern across upperwings and dark tail tip. Underparts are white with very narrow black margins to wings. Many birds off Mexican coast are in wing molt.