Why do gazelles live in herds?

Wildebeest, Zebras and Gazelles are found in herds because of protection from predators such as lions. With increased numbers there is less likely a chance the predator will succeed because of all the movement, except with old or weakened animals. It also has to do with camouflage, such as with the Zebra. When in a large heard their black and white stripes intermix and it confuses the predator about where one starts and one stops.