Male allocare among nonhuman primates has frequently been investigated from the perspective of the caretaker. Here we examined whether male allocare relates to environmental factors or the females＇ energetic stress. We researched the possible differences of allocare between sexes in free-ranging black-and-white snub-nosed monkeys （Rhinopithecus bieti） in Tibet. A combination of stepwise least squares regression analysis was used to identify the influence of ecological factors （temperature, rainfall, etc.） and infant age that best account for seasonal variation of allocare. The results indicate, except for the functions of infant age, however, that male allocare is a negative function of temperature and female allocare is a positive function of temperature. Specifically, we tested the energetic stress hypothesis, which predicts that the energetic burden of females in a severe environment favour an increased rate of male allocare during the seasons of high energetic stress. We analyzed the allocare difference between high energetic stress season （Mar - Apr）, when temperature was low, food availability was scarce, and infants were young, and low energetic stress season （Jun - Aug）, based on data obtained during June 2003 - June 2004. Our results supported the energetic stress hypothesis because male allocare in high energetic stress season was higher than that of in low energetic stress season and female allocate was reverse. Therefore, we propose it is the energetic stress on female that make male allocare possible. Male take these interests for other aims and meet some functional hypothesis, which are addressed from the perspective of the male.
