For example, a polar bear's companion died. There she was left, in a zoo, her natural territory of hundreds of miles reduced to a few metres with an ice-flow painted on the wall, and rocks painted white. She is going mad, spending most of the day retracing the same steps again and again. Such pointless repetitive movements have also been noted in mentally ill people. With nothing to do, these zoo animals become psychotic.
Surplus animals are a problem for zoos.
Many animals are bred simply to attract visitors, and many will be killed or disposed of at the end of the season. Newborn or young animals are often culled. Animals may be shunted from one zoo to another. Surplus stock of certain species are 'recycled' - fed to other animals. Chester Zoo and Cotswold Wildlife Park have supplied bison and ostrich respectively to exotic meat farms.