The breeding season in red deer when males compete for females is called the rut.
During the rut, mature male red deer, known as stags, compete for access to females, or hinds. They roar, posture, assess rivals by walking in parallel, and may clash antlers if neither animal backs down. Dominant stags can gather and defend groups of hinds, while younger or less powerful males often remain at the edge of these groups and look for opportunities to mate.
The rut is driven by seasonal reproductive changes, including rising testosterone and female estrus. In red deer it generally begins in late summer or early autumn and can continue into early winter, depending on location. Roaring is especially important in wooded habitats, where sound can advertise a male’s size and condition even when vegetation limits visibility.
“Estrus” refers specifically to the period when a female is sexually receptive, not the entire breeding season. A lek is a display arena used by some species, including fallow deer, but red deer typically compete through roaring, harem defense, posturing, and antler combat. Males may lose substantial body weight during the rut because they spend little time feeding.