Reproductive and social behavior of marmosets with special reference to captive breeding.
The field studies reviewed above raise some doubts about the laboratory concept of the extended family as the basic social unit of the Callithricidae. As Dawson [6] suggests, wild groups might more closely approximate artificial laboratory groups. They probably consist of a dominant, monogamous breeding pair, its dependent offspring and separate hierarchies of subdominant males and females who stay associated with the group for various lengths of time. Some of these subdominants might be offspring or relatives of the breeding pair. As the field studies show, these groups are more or less open to immigrants coming from other groups. They possibly tolerate transient relatives more easily and for longer periods of time than nonrelated individuals. In spite of the relative tolerance of wild groups towards strange conspecifics, it appears most practical to maintain laboratory breeders as families and remove the offspring after they have participated in the care of their younger siblings. In this way their reproductive capacities can be utilized as soon as their parental behavior has developed adequately. Moreover, possible losses caused by keeping nonrelated adults of the same sex together are avoided. As pointed out above, some species are very aggressive towards strange adult conspecifics and some seem to defend territories in the wild. It seems advisable therefore to house them in cages which provide a certain degree of isolation from neighboring groups. We have found this to be more important in S. fuscicollis than in C. jacchus, particularly in densely populated colony rooms. We therefore house our animals in cages which allow no visual contact with any other group, and by doing so have reduced the general level of excitement in the colony room. We believe that aggressive displays between groups are responsible for a large amount of redirected aggression between mates and for some of the abortions we have seen in our colony. Moreover, Rothe's [28, 29] observation that the parturient female withdraws from her group and gives birth in relative isolation should be taken into consideration when designing breeding cages. Although not all individuals of all species might show this behavior [see 32] it seems to be widespread enough to be an important factor in breeding efficiency and might figure in some of the infanticides observed by us and other authors.