Taxonomy
Biologists have until recently stated that Red Deer and Wapiti (or Elk) are the same species forming a continuous distribution throughout temperate Eurasia and North America, based on fertile hybrids that have been produced under captive conditions. Animal behaviour is generally different in captivity than in the wild, and the assumption that the same results would happen in the wild as in captivity is not necessarily the best test methodology to determine speciation.
Recent DNA studies conducted on hundreds of samples from Red Deer and Elk subspecies concluded, that that not more than 9 distinct subspecies of Red Deer exist and that they should be considered to be two separate species. The Wapiti or Elk from Northern and Eastern Asia and North America and the Red Deer from Europe, western Asia and North Africa represent two distinct species. Surprisingly the Elk is more closely related in DNA to the Sika Deer and to Thorold's deer than to the Red Deer.

Subspecies
Additionally there are some central asiatic subspecies (Tarim group, including Bactrian deer and Yarkand deer), which are geographically isolated from Wapitis and western Red Deer by the Takla Makan and the Pamir Mountains. They represent a primordial subgroup, which is genetically more related to the Red Deer than to the Wapitis. It remains unclear which clade the Kashmir stag belongs in, though it, in terms of zoogeography, is most likely to belong in the central Asian group.
The International Union for Conservation of Nature and Natural Resources originally listed nine subspecies of Red Deer (Cervus elaphus): three as endangered, one as vulnerable, one as near threatened, and four without enough data to give a category ("Data Deficient").

Behavior
Mature Red Deer (Cervus elaphus) usually stay in single-sex groups for most of the year. During the mating ritual, called the rut, mature stags compete for the attentions of the hinds and will then try to defend hinds that they attract. Rival stags challenge opponents by belling and walking in parallel. This all ows combatants to assess each other's antlers, body size and fighting prowess. If neither stag backs down a clash of antlers can occur, and stags sometimes sustain serious injuries.
Dominant stags follow groups of hinds during the rut, from August into early winter. The stags may have as many as 20 hinds to keep from other less attractive males. Only mature stags hold harems (groups of hinds) and breeding success peaks at about 8 years of age. Stags 2-4 years old rarely hold harems and spend most of the rut on the periphery of larger harems, as do stags over 11 years old. Young and old stags that do acquire a harem hold it later in the breeding season than those stags in their prime. Harem holding stags rarely feed and lose up to 20% of their body weight. Stags that enter the rut in poor condition are less likely to make it through to the peak conception period.
Male European Red Deer have a distinctive "roar" during the rut, which is an adaptation to forested environments, as opposed to male Wapiti (or American Elk) which "bugle" during the rut in adaptation to open environments. The male deer roars to keep his harem of females together. The females are initially attracted to those males that both roar most often and have the loudest roar call. Males also use the roar call when competing with other males for females during the rut, and along with other forms of posturing and antler fights, is a method used by the males to establish dominance. Roaring is most common during the early dawn and late evening, which is also when the crepuscular deer are most active in general.

Breeding, gestation and lifespan
Red Deer mating patterns usually involve a dozen or more mating attempts before the first successful one. There may be several more matings before the stag will seek out another mate in his harem. Females in their second autumn can produce one and very rarely two offspring per year. The gestation period is 240 and 262 days and the offspring weigh between 15 and 16 kilograms (33 to 35 lb). After two weeks, calves are able to join the herd and are fully weaned after two months. Female offspring outnumber male offspring more than two to one and all Red Deer calves are born spotted, as is common with many deer species, and lose their spots by the end of summer. However, as in many species of Old World Deer, some adults do retain a few spots on the backs of their summer coats. The offspring will remain with their mothers for almost one full year, leaving around the time that the next season offspring are produced. The gestation period is the same for all subspecies.