As Fall approaches Bull Elk start to gather cows together for the breeding season. They then protect the harem from other bulls who try to take cows from their harem. This establishes a peeking order where only the dominant and strongest bulls breed and preserve the blood line. Most of the time the herd bull will run off the smaller bulls but on occasion a bull of the same stature will challenge for the breeding rights. The breeding season occurs in the Fall so the calves will be born in the spring and have a better chance of survival.
Included are a few images of the challenge.