With keepers to feed them, vets to cure them, and no predators (捕食者)to eat them, animals in a zoo usually live much (long) than animals in the wild. Zoo life is safe, but it can also be boring.
In the wild, survival is full-time job, consisting of finding food, taking care of babies, and steering clear of all the things that might want to eat them. (compare) with their wild cousins, says one zoo vet, zoo animals are unemployed.
Scientists (observe) animals in their natural environments realized that some zoo animals were doing all sorts of (nature) things those species in the wild don't do. Tigers paced back and forth (end). Elephants moved their heads up and down. These are signs of boredom and stress. And scientists have learned that being stressed out can actually make animals and people sick.
Giving zoo animals food and shelter (be) not enough to keep them healthy. They also need something (do). These days, problems like pacing are less common because zoos try to make life interesting for animals that live there, with habitats, games, and even toys encourage natural skills and behaviors. These things are just as important for the animals' good health a proper diet or a visit from the vet.
