No one is completely certain why some animals such as bighorn sheep segregate themselves into male and female groups. Researchers are testing a few hypotheses. A key observation in this work is the difference between the size of males and females, with males almost always being larger. This is a type of sexual dimorphism where males and females have different size, shape or appearance (humans are very sexually dimorphic). Differences in body size can lead to other important differences between males and females that may cause them to form separate groups, such as:

Large animals are less likely to be eaten by predators, so females, especially with lambs, might need to use safer areas.

Large sheep might be able to eat more fibrous (tough, low quality) food, because their guts are larger. Therefore females may have to use areas where higher quality food is available. Also because females are bearing and nursing young, they may need extra nutrition.

Males and females may have very different behaviors that cause them to form single sex groups. For example, male sheep have to learn to fight for females during the mating season. They learn this from other males, which may encourage them to form single sex groups.

There are some other variations of these ideas that are being explored by researchers. I am sure that if you thought about it, you might be able to think of a few others.

Another thing to think about is how you might test these ideas. What observations would you make? What information would you gather?