Streaked Shearwaters Calonectris leucomelas breed along the northwest Pacific coast, and winter in Australia and Southeast Asia. Previous studies at nesting sites on islands off the Japanese coast have indicated that males and females give different mating calls. This research, implemented at a breeding colony on Kanmuri Island, Kyoto Prefecture, showed that there were differences in the external measurements of Streaked Shearwaters giving low-pitch and high-pitch vocalizations. A discriminant function: D=216.400-2.318×THL-4.074×BW+2.007×NAL-1.929×BD, where THL is total head length, BW is width of bill at anterior edge of nostril, NAL is nalopsi and BD is depth of bill at anterior edge of nostril, was derived from external measurements of adult shearwaters giving low-pitch (41 birds) and high-pitch (41 birds) calls. D was positive for the birds with low-pitch calls and negative for the birds with high-pitch calls. This function proved reliable for 97.6% of the low-pitch individuals and for 95.1% of the high-pitch individuals, thus vocalization may be a useful means of sex identification in the field.