Sex ratios at birth in a Micronesian Atoll population.

The recent suggestion that typically masculinized sex ratios at birth in Micronesian populations may be related to a distinct "Micronesian pattern" of life-course coital behavior is applied to data on the sex ratio of livebirths on Butaritari Atoll in Kiribati. The data show that sex ratios on Butaritari are highly masculinized and do not vary significantly with changes in maternal age. However, there is a discernible relationship between the length of closed intervals preceding male and female births. The lack of age-related change in sex ratios in the Butaritari sample is inconsistent with ethnographic data regarding levels of marital coital activity in relation to increasing age and marriage duration. The Butaritari sex ratio data is argued to support the suggestion of a "Micronesian pattern," although it is posed that further tests of this association are required.