During the late summer the majority of the bulls are segregated from the cows, in what is known as bachelor groups. They will feed in the morning and the evening when the temperatures are cool, and then retreat to the timber to rest in the shade. Their anlers have grown back after shedding them in April and May, and are still covered in velvet. It is now that the equinox is starting to take place and the daylight is getting less and less every day. The shortening of daylight will trigger the elk's biological clock and the rut will begin. As the light decreases in the fall, glands are stimulated (by the amount of daylight which comes in through the eyes) and these glands will release hormones. In the cows, this will begin the oestrous cycle. In the bulls, there antler growth will stop, the velvet will dry up, their necks will swell, and their testicles will fill up with seman.

The bulls first shed their velvet, their antlers are white. During the rut the antlers will darken, or become stained from dirt, mud, bark, sap, and blood, turning them to various shades of browns to almost black. The bulls will be less and less social with their summer time companions. They will soon begin to seek out the cows and form their harems. Only the largest and stongest of the bulls will become herd bulls and be able to take and hold a herd of cows. This is natures way of insuring that only the best bulls do the breeding. Their genes can now be passed on for future gerations of elk.

During the rut, a bulls neck and hump may swell to twice it's normal size. The hair on the mane will grow darker and longer, and the antlers will be dark with white tips. All these features will help the bulls to look more massive than they already are. He will be very aggressive with outstretched neck, raised hackles, deep bugle, and shake his antlers violently. This will show him as being an overwhelming opponent, and not to be messed with.

These bulls will seek out the cows and if they are not already taken by a larger bull, he will claim possession of them. He will chase off any smaller bulls, usually without having to fight, but with just his massive size and aggrssiveness. As the height of the rut passes, the herd bulls will wander off and once again form bachelor groups. At the end of the rut, a bull will have lost roughly 100 pounds and will need to feed heavily to replace the lost stores of fat needed for the upcoming winter months.