The Degu (Octodon degus) is a small caviomorph rodent that is native to Chile. It is sometimes referred to as the Brush-Tailed Rat (although not closely related to the rat family) and is also called the Common Degu, to distinguish it from the other members of the genus Octodon. Other members are also called degus, but they are distinguished by additional names. The name "degu" on its own, however, indicates either the genus Octodon or, more usually, O. degus. Degus are closely related to the chinchilla and guinea pig, also placed in parvorder Caviomorpha.
Degus are highly social. They live in burrows, and, by digging communally, they are able to construct larger and more elaborate burrows than they could on their own. Degus digging together coordinate their activities, forming digging chains. Females living in the same group have been shown to spontaneously nest communally; they nurse one another's young. They spend a large amount of time on the surface, where they forage for food. When foraging, their ability to detect predators is increased in larger groups, and each animal needs to spend less time in vigilance. Degus exhibit a wide array of communication techniques. They have an elaborate vocal repertoire, and the young need to be able to hear their mother's calls if the emotional systems in their brains are to develop properly. They use their urine to scent mark, and experiments have shown that they react to one another's marks.
Degus are seasonal breeders; the breeding season for wild degus begins in the Chilean winter, with pups born mid-late spring. It is also speculated that female degus are induced ovulators. Female degus are pregnant for approximately ninety days, having a long gestation period compared to other rodents such as hamsters. Litters usually contain four to seven pups, but size can range from one or two up to fifteen young. Degu pups are born relatively precocial, fully furred and with eyes open, and their auditory and visual systems are functional at birth.
Unlike other octodontids, degus are diurnal, and they have good vision. Their retinas include rod cells and two types of cone cells, one of which has its peak sensitivity in the ultraviolet region of the spectrum. Behavioral experiments have shown that degus are able to discriminate ultraviolet light from the wavelengths visible to humans. It is likely that this ultraviolet sensitivity has a social function, since both their ventral (stomach) fur and their urine are highly UV reflective.
Degus are herbivores, feeding on grasses and browsing the leaves of shrubs, though they will also take seeds. Their feeding rate is constrained by the rate at which they can digest this relatively low quality food, and this varies between food types and environmental conditions, and like some other herbivores such as rabbits, they show coprophagy, chewing their own feces so as to extract more nutrition from them. This also serves to maintain healthy gut function during times when food is scarce. Although they are active by day, in high summer they do not leave their burrows in the middle of the day, and in hot conditions they forage as quickly as possible instead of maximizing the quality of their food. They tend to forage in shaded areas, though this tendency is reduced in the absence of predators. In open areas they spend more time being vigilant, so their effectiveness as foragers is reduced. Degus have a significant impact on the vegetation in areas where they live, and as the only rodent foraging by day, their numbers influence the food supply available to the more numerous nocturnal rodents. However, numbers of all species of degu have been declining over recent decades, most likely due to human disturbance. Degus should not be fed a diet full of sugar, because due to their body's inability to process sugar, it will cause diabetes to develop.
As pets and research subjects
Degus are prone to diabetes due to their divergent insulin structure. For this reason, they are used frequently for research in this field. The degu's popularity as a pet was influenced by this research, as animals were imported into various countries for research and study.
Degus are also used extensively as laboratory animals. Neuroscientists at the Riken Institute in Tokyo, Japan, used degus in research on tool-using in animals with good eye-and-paw coordination, in which the rodents were trained over a period of two months to use a tiny rake to retrieve out-of-reach seeds.
Degus have become popular as pets, though until very recently they were seldom found in pet shops. Their advantages over traditional small pets are their diurnal habits, bubbly personalities, the haired tail (as compared to rats and mice) and their lifetime: they are said to live up to 13 years under ideal circumstances (though a poor gene pool/genetic background often reduces a pet degu's lifespan significantly). The average lifespan of a degu in captivity is said to be around 5-8 years of age. One disadvantage of the degu as a pet is that they gnaw much more than most other common rodent pets, especially through plastic-bottomed cages typically found in pet stores. Untame degus, as with most small animals, can be prone to biting, but their intelligence makes them easy to tame. Degus often 'groom' their human owners, by a gentle nibbling action, but they can give a defensive bite if they feel threatened.
Degus are mainly known for their brown fur, but through genetic mutations and intentional inbreeding, there have been degus with white, cream, black, blue, and tan colored fur.
It has been suggested that the family Octodontidae, to which the degu belongs, should be reclassified into the order Lagomorpha (rabbits, hares, and pikas). However recent studies in molecular systematics (e.g. Opazo, 2005) suggest that it is correctly placed among the caviomorph rodents.