proteins, and protein requirements for these species have been estimated at around 20% (Tardif and others 1988). Coprophagia has been reported to be associated with lower percentages of dietary protein (Flurer and Zucker 1988). Most laboratories housing callitrichids feed a commercial diet high in protein (25%) to substitute for the highprotein content of insects. Vitamin D3, found in insect chitin, is important in promoting absorption of calcium and other minerals. Callitrichids cannot metabolize vitamin D2, so diets fed to them in captivity should have adequate concentrations of vitamin D3 (Hunt and others 1967a, b). Many colonies use lighting that mimics the full spectrum of sunlight to promote vitamin D3 synthesis and absorption.
Several laboratories have maintained colonies on unsupplemented single diets. Such diets might fulfill all the nutritional requirements of these primates, but they do not always appear to be palatable enough to be eaten by all individuals in sufficient amounts. Primates that naturally forage on a large variety of foods are adapted to variety and might need variety to stimulate intake. In many colonies, additional feedings of high-protein foods—such as cottage cheese, yogurt, chicken, ground beef, and mealworms—are provided early in the morning and in late afternoon. A variety of fruits and high-protein foods also will accommodate individual dietary preferences and allow each individual access to some highly preferred foods while maintaining overall nutritional balance. Individual food preferences should be carefully monitored. Although most animals will consume a balanced diet when given a choice among foods, some might reject all other foods in favor of fruit. For such animals, it is advisable to exclude fruit from the first feeding of the day and provide it in the late afternoon. All fruits and vegetables should be carefully washed before feeding them to the monkeys.
Animals 15 years old or older often have dental decay or loss of teeth and might be unable to eat hard pellets. They must be provided with food that they can chew. Aged animals might also have special nutritional requirements, such as an increased need for vitamins.
Marmosets and tamarins are small animals with a high metabolic rate. In the wild, animals sleep in hidden locations for 13 hours per night. Feeding rates are high in the hours before sunset and immediately after animals arise in the morning. It is important that captive animals have fresh food available early in the morning and in late afternoon.
All callitrichids are social, but most live in small groups, which often consist of a single reproductively active pair and their offspring. In wild populations, some variability has been noted, but except for Goeldi's monkeys, which do well with more than one breeding female present, a single breeding pair and their offspring do best in captivity.
The skin of marmosets, tamarins, and Goeldi's monkeys contains specialized