The size of adult elephants leaves them invulnerable to wild animals. Humans are the only predators to adult elephants but calves are susceptible to be snatched away by lions and hyenas. If they sense a predator nearby, the largest cows instinctively herd the calves into a bunch around the matriarch. Next, they form circles around the cluster which creates protective layers that are impossible for predators to penetrate. (Estes, 1999)