Mountain goats reach sexual maturity at about 30 months. Nannies in a herd undergo synchronized estrus in late October through early December, at which time females and males participate in a mating ritual. Mature billies stare at nannies for long periods, dig rutting pits, and fight each other in showy (though occasionally dangerous) scuffles. Nannies often ignore young billies, who try to participate but are discounted in favor of older partners. Both females and males usually mate with multiple individuals during breeding season, although some billies try to keep other males away from certain nannies. After the breeding season is over, females and males move away from each other. Nannies form loose-knit nursery groups of up to 50 animals. The adult billies leave, often alone or with two-three other billies.