Male Red Deer retain their antlers for more than half the year and are less gregarious and less likely to group with other males when they have antlers. The antlers provide self defense as does a strong front-leg kicking action which is performed by both sexes when attacked. Once the antlers are shed, stags tend to form bachelor groups which allow them to cooperatively work together. Herds tend to have one or more members watching for potential danger while the remaining members eat and rest.

After the rut, females form large herds of up to 50 individuals. The newborn calves are kept close to the hinds by a series of vocalizations between the two, and larger nurseries have an ongoing and constant chatter during the daytime hours. When approached by predators, the largest and most robust females may make a stand, using their front legs to kick at their attackers. Guttural grunts and posturing is used with all but the most determined of predators with great effectiveness. Aside from man and domestic dogs, the Wolf is probably the most dangerous predator that most European Red Deer encounter. Occasionally, the Brown bear will predate on European Red Deer as well. Eurasian Lynx and wild boars sometimes prey on the calves. The leopard in Asia Minor (now extinct) probably preyed on East European Red Deer. Both leopards and lions, which are now extinct in the Atlas Mountains, probably once preyed on Barbary Stags.

DNA studies on Subgenus Cervus (Red Deer, Asian Red Deer, and Wapiti subspecies) 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 samples from Red Deer and Elk subspecies determined that there are three distinct species of Red Deer and divides them into an Western (European), Central (Himalayan/Tibetan), and Eastern (North Asia, East Asia, North America) species grouping. The western species is the European Red Deer and includes the deer that are found in Europe, Asia Minor, and North Africa. The central species is the Central Asian Red Deer that inhabits temperate riparian vegetation corridors surrounded by deserts and temperate mountainous environments of the Himalayan Mountains and the Tibetan Plateau of Central Asia. The eastern species is the Wapiti (or Elk) whose range is from Northern and Eastern Asia into North America. Altogether, the study concluded that not more than 9 distinct subspecies of Red Deer exist and that the eastern, central, and western groups should be considered to be three separate species. Both the Central Asian Red Deer and East Asian Red Deer/Wapiti (or Elk) are more closely related in DNA to the Sika Deer than is the European Red Deer. Biologists have not adopted a general consensus that there are three distinct species.