This is when the males, known as Stags (Red deer) or Bucks (Fallow deer), compete for dominance of the herd and the right to mate with as many females, known as Hinds (Red) or Does (Fallow), as they can. Fuelled by testosterone, the males give out a guttural roar, called bolving. This is to attract females and to warn off other males. If another male won't back down, the two will parallel walk and size each other up. They will then lock antlers and push against each other, to see who is the strongest. This can go on for sometime until one admits defeat and backs down. Injuries are common and sometimes fatalities occur.
The victor will sniff and lick the air picking up the females scent and then knows which females are receptive to mating. He can mate with upwards of thirty females!