Viscachas and Chinchillas: Chinchillidae

The mountain viscacha and all the chinchillas eat, sunbathe, and groom while sitting erect on their hindquarters. The plains viscacha and all the chinchillas look for food at sunset and throughout the night, but the mountain viscacha is alert and active by day and hides by night. All of these animals live in colonies of some sort, but some are more tightly knit and structured than others. For instance, the plains viscacha is compelled to use a communal burrow system, and the colony is dominated by a strong male and an assistant he chooses from the fifteen to thirty members of the family group. On the other hand, chinchillas and mountain viscachas have a more relaxed social structure in which the colony is more spread out and can consist of from four up to 300 animals, with different burrows housing individual family groups. As colonial animals, there is always at least one individual on guard to watch for predators and other dangers. The mountain viscacha has a warning call that sounds like a high whistle, whereas the plains viscachas have a more varied palette of sounds, including a characteristic "uh-huh" sound, numerous whines, and their own species-specific warning calls. All six species have been observed taking dust baths and engaging in play chases, and all but the plains viscacha are amazingly agile as they jump among rocky outcroppings.

Female chinchillids are very aggressive to other females and even many males, with much growling, teeth chattering, and urinating, although there are rarely serious fights in the wild. They have unusually long gestation periods for rodents of their size, carrying their young 90 to 154 days before giving birth to one to six pups. The average female, which reaches sexual maturity (able to mate) at from eight to fifteen months, can produce one to three litters every year. Pups are born with open eyes and are fully furred, and their mothers nurse them for six to eight weeks. This species usually has more than one mating partner during the breeding season.