Condition-dependent reproductive success in bighorn ewes

Individual bighorn ewes (Ovis canadensis) at 4-14 years of age were 1.5% heavier preceding years when they weaned a lamb than preceding years when their lamb died before weaning. Intra-individual differences in mass between years of successful and unsuccessful reproduction appeared independent of a ewe's multiyear average mass. Relative mass loss both in the winter before and in the winter after a given reproductive episode increased with reproductive success. Long-term monitoring of individual mass and reproductive success is a promising technique to study life histories in capital breeders, because it allows to partially account for differences in reproductive potential.