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. 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.