"Fieldnotes," November 17th & 18th, 2013:"Ungulate Mating Seasons," by Milo Burcham / Caroline Kurtz. http://www.montananaturalist.org/
"Young ungulates have to be born at the same time every year, which is around mid-May to mid-June for most species in Montana. The state's breeding calendar is a full one, beginning with the largest mammal in the state, which requires the longest time for young to develop: the bison. The bison rut takes place in August, before we are even thinking of fall. The ruts of elk and moose are next, in September and early October. Mule deer, white-tailed deer, bighorn sheep and mountain goats all go through their rutting periods in mid-November. They are smaller and have shorter gestation periods than their larger relatives. The exception to the rut-timing schedule are pronghorn, the smallest of Montana's ungulates. They mate about the same time elk and moose do."