The Black-tailed Mule Deer (Odocoileus hemionus) are found on the western Great Plains, the Rocky Mountains, Southwestern United States and the West Coast of North America.
Deer are ungulates, meaning they are hooved. They are also ruminants which means they eat and send their food to the rumen; one of its stomachs. Later, it regurgitates the cud (food) from its rumen, chews it and sends it to its other stomach to digest. Male deer, like moose and elk, have antlers. Antlers are made of bone which are shed and regrown each year. (Animals like sheep, goats, cattle, and antelope have horns. Horns are made of bone covered with keratin which are permanent; not shed and regrown.) The prongs on an antler are referred to as points; a 6 point buck has 3 prongs on each antler.
Male deer are called bucks, female deer are called doe and the babies are called fawns. During most of the year, deer segregate themselves by sex; bucks in groups and doe, along with their young, in separate groups.
Each year, deer go through a reproductive cycle that begins with the “rut”[i]. The rut is the time when male deer fight for the right to breed with a harem of females and concludes with impregnated doe. As the rut commences and bucks have regrown their antlers, the bucks attempt to form a harem. One buck may challenge another for the right to breed with a harem. Bucks will lock antlers and push and fight until one is pushed backwards and loses the challenge. It is a dangerous time for bucks; they can become permanently injured. The ultimate winner breeds with the females as they enter estrus. Gestation is about 200 days.
In mid-to-late winter, the bucks drop their antlers. When the antlers regrow, they are covered with a furry skin commonly called velvet. When the antlers have completed their growth, the velvet dries and causes irritation for the bucks. The bucks rub their antlers against a tree to remove the velvet.
About the time autumn begins, when the fawns have grown and the bucks’ antlers have regrown, the rut begins again.
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 Information obtained from: https://www.wildlife.ca.gov/Regions/6/Deer/Natural-History