Hyenas are mainly active at night but can be seen during the day in the vicinity of lion or cheetah kills, waiting their turn to feed on the carcasses. Hyenas are not only scavangers. They can hunt too, often forming packs to bring down wildebeest, zebra, and gazelle. They can reach speeds of almost forty miles per hour. Hyena pups are born in burrows in litters of up to four. Hyenas communicate through a variety of calls including howls, screams, and their famous "laughs". Humans are their main enemy.