In our area, the rut occurs in the last week of November and the first week of December and most kids are born between May 21 and June 7. Estrus and birth are synchronized among the females of the herd. This may aid survival. Predators may have difficulty killing a large number of newborn kids spread out over a large area of rough terrain all at the same time.
Each nanny finds an isolated and inaccessible ledge to give birth. Single births are most common but twins do occur. Kids weigh just 7 pounds (3.2 kg) at birth. Kids can run and leap within hours of birth. The nanny will stay with her kid in isolation for three to five days then will return to the herd. Kids are weaned within a few months. A small kid will take shelter under the nanny if threatened. The kid will accompany its mother for one year until the nanny is ready to give birth to her next kid. If the nanny does not become pregnant, she may allow her kid to stay at her side for a second year.
Mountain goats reproduce at a slow rate. Nannies only have limited opportunities to bear young. They become sexually mature at 3 years and can live up to 14 years of age but nannies may not have a kid every year. On average, only 60% of mature females will give birth. In addition, young kids have a low rate of survival over their first winter – as low as 40%. In their second winter, up to 50% of yearlings fail to survive. The result is that if a herd of mountain goats suffer a large loss of individuals due to avalanche, hunting or predation, it may take many years for the herd to rebuild its population. Older females have a better chance of successfully producing young that will survive. The herd depends on mature females.