Social Behavior and Reproductive Strategies

We describe the behavior and reproductive strategies for mountain sheep. Mountain sheep are sexually segregated outside the rut and rely on habitat near escape terrain to avoid coursing predators. Both sexes are highly philopatric and permanent dispersal is rare. Adult females join their natal group but do not preferentially associate with kin. Female reproductive strategy is conservative. Females favor their own survival over allocation to their current lamb. When resources are scarce, females delay primiparity from 2 to 4 years of age, and lactating females appear to produce less milk so that lamb mass gain decreases and lamb survival declines. Lambs born in the year after their mother had weaned a lamb have lower growth and survival. The mating system involves serial female-defense polygyny by highly dominant males that defend a single estrous female at a time. Subordinate males use alternative mating tactics such as coursing, attempting to separate the female from the defending male. The defending male has a 40%–50% probability of siring the lamb. Subordinate males using alternative mating tactics share the remaining paternities. The positive correlation of horn size and siring success is weak until about age 6 and strong for older males. The mating system and the age-specific relationship between horn size and mating success make mountain sheep highly susceptible to hunting-induced evolution of smaller horns if trophy harvests are intense. Male breeding migrations provide gene flow among populations and can be blocked by human development, leading to loss of genetic variation.