Biological instinct is driven by three things to stay alive to find food and to breed passing on a genetic legacy. But competition for mating rights can be fierce. Animals grow display structures and weapons to help them impress the opposite sex.
All animals no matter how big or small must face a daily struggle to find food. During harsh winters and devastating droughts those pressures escalate and when resources are running low sometimes the only option is to fight.
There is an expression that there is always a bigger fish. All animals fit into a food chain feeding on those below but there is nearly always another link in the chain something that wants to eat them.
Sometimes just staying alive is a fight especially in the bleakest polar regions the driest deserts the highest mountains and the sharpest season changes. But instincts run deep and animals battle the environment and each other to stay alive.