scent glands. Glands are typically found in the anogenital region, the suprapubic area, and above the sternum and possibly on the face at the borders of the mouth. The oily secretions from these glands, mixed with urine and genital discharge, are deposited on all items in the animals' environment, and in some species on the bodies of cagemates, through scent-marking behavior. Different species use different glands for scent-marking; moreover, the context in which scent-marking is exhibited varies somewhat among species. Geoffroy's tamarins, cotton-top tamarins, and Goeldi's monkeys also show a self-marking behavior. The scent marks are important components of the communication systems of these primates. The marks can contain information on species, subspecies, and individual identity, on hormonal condition, on social rank, and on the age of the scent. Scent communication plays a role in a variety of social and sexual interactions and in attachment between group members and the infants that they care for. Scent from a breeding female also contributes to the suppression of ovulation in nonbreeding females of several species. As is true of other mammals, monkeys might feel comfortable in their home environment with their own scents present (Epple and others 1993).
Scent-marking rates increase when conspecific intruders are present and during territorial encounters. The close proximity of neighboring groups in a colony situation can arouse some animals so strongly that they scent-mark excessively, soiling themselves and their cagemates. In such cases, the problem can sometimes be corrected by switching neighbors or placing the animals next to a group of another callitrichid species or an empty cage.
Callitrichids and Goeldi's monkeys typically show little or no sign of estrus and no obvious changes in outward physical appearance or in vaginal cytology during estrus. Estimation of gonadotropins and of ovarian steroids in blood, urine, or feces shows that female ovulatory cycles vary greatly, from 15 to 28 days. Mating behavior does not closely reflect a female's hormonal state. Mating might peak during the periovulatory phase but also occurs at other times, even during pregnancy, when a period of behavioral receptivity can occur. Mating is typically very quick. Mating solicitation is indicated by rapid tongue flicking and looking over the shoulder by the female, and both partners might tongue flick during copulation (Epple 1978).
Callitrichids have been assumed to be monogamous (one male mating with one female), but the results of several recent field studies have found both polyandry (one female mating with more than one male) and polygyny (one male mating with more than one female). However, a survey of captive cotton-top tamarin colonies found few departures from monogamy, and the departures did not lead to stable breeding conditions (Price and McGrew 1991). Under captive conditions, callitrichid groups contain a single breeding female. Reproduction is