TWINNING AND FETAL SEX-RATIO IN MOOSE - EFFECTS OF MATERNAL AGE AND MASS

To evaluate hypotheses concerning the effects of maternal characterist ics on litter size and offspring sex ratio in a polygynous mammal, we examined how female age and mass affected the number and sex ratio of fetuses in moose (Alces alces). We analysed 420 fetuses collected from 297 females killed in Finland. Females that carried two fetuses were older than females with one fetus, while mass did not affect litter si ze. Sex ratio was not conclusively linked with maternal quality. The o verall lack of difference in the sex ratio (no male bias among fetuses carried by the heaviest females) can be explained by the rather low d egree of polygyny and the lack of intense female-female competition fo r a limited food supply (no female bias among fetuses carried by the h eaviest females).