^I've seen those

. But since all they do when they migrate, hunt, reproduce and so on is follow their instincts, maybe that enjoyment is also something that serves survival. They don't get lost in it like humans who become addicted to pleasure. It's the way they are programmed. During migrations many animals get killed but it's natural selection. They are like organic robots in their survival, so why wouldn't it be so also in their freetime activities. Okay, maybe they enjoy everything. I know life would be easier if I were programmed to do what's most sensible in every situation.
When wild animals gets put in cage and humans do stuff to them, that's another story. That's when they get mental health problems.