Gerbils are long tailed nocturnal small rodents that come from desert environments. The commonest pet species is the Mongolian gerbil (or "jird"). In the desert areas of China and Mongolia gerbils would tolerate a wide range of temperatures, but with low humidity. They have extensive burrow systems and live as family groups. Most gerbils are sandy (agouti) coloured with a dark tip to their furry tail. There are also black gerbils and other colour mutants including albino, piebald and cinnamon are seen. They usually prefer to associate with their own colour type. Gerbils as pets are relatively robust, certainly they tend to suffer less disease conditions than hamsters. They are relatively odourless, clean and have simple needs. They are mainly nocturnal and are active, inquisitive creatures. Generally they are fairly docile and rarely bite. However they do chew and gnaw through wooden cages. Gerbils will foot drum (males more than females) as a method of communication. Gerbils' front long incisor teeth continue to grow throughout life, but the cheek teeth do not.