If the amount of available food and water decreases in an environment then animals may leave that environment to find food and water.
Famines occur when there is a general shortage of food.
If there is a famine in an environment, then animals may leave that environment.
Animals may leave an environment during which event?

a: Birth
b: Winter
c: Tropical
d: Rainstorm
e: flooding
f: Hibernation
g: Famine
h: storms