II  Social Organization

Chapter Summary

Social Structure

Although there is much debate about callitrichid social organization (Price & McGrew, 1991; Savage & Baker, 1996), cotton-top tamarins are successfully housed as monogamous breeding pairs and their offspring in captivity. This choice of social structure is the result of many years of investigating reproductive strategies of wild and captive callitrichids (see Snowdon, 1989). Studies attempting to integrate adult animals into existing stable families have failed since intruding animals are met with intense aggression by resident animals (de la Ossa et al., 1988; French et al., 1984). However, evidence of deviations from monogamy in captivity (Price & McGrew, 1991) and in the field (Savage et al., 1996) have been observed. Multiple breeding females within groups are common when their is some disruption within the breeding pair or group (death of a mate, introduction of a step-parent, immigrating adult male) (Price & McGrew, 1991; Savage, 1990; Savage et al., 1996).

Alternative Housing Options

Due to breeding recommendations and the variation found in the population, cotton-top tamarins can be housed in a variety of social conditions other than the standard breeding pair/family group.

Father + offspring (e.g. after the death or removal of the breeding female). This social grouping generally remains stable. Most daughters remain reproductively suppressed under these conditions, however, there have been noted exceptions. Daughters over 14 months of age should be contracepted if they appear to have 1) a highly active scent gland (darkly pigmented and secreting sebum); 2) are actively scent marking their environment; 3) are observed copulating with a male.

Mother + offspring (e.g. after the death or removal of the breeding male). This social grouping generally remains stable. The breeding female will continue to cycle and it is rare that copulations are observed. However, if copulations between mother and sons are observed, the female should be contracepted.

Iso-sexual groupings Housing same sex pairs of animals is fairly routine for animals that have been reared in family groups. Hand-reared or improperly socialized animals may not be appropriate for this type of grouping. In general, do not pair more than two unrelated animals. However, sibling groups larger than two animals are generally successful.

Single sex-mixed callitrichid group A single cotton-top tamarin can usually be successfully housed with a single individual of another callitrichid species. A common marmoset (C. jacchus), golden-head lion tamarin (L. chrysomelas), and Goeldi's marmoset (Callimico goeldii) have been successfully housed with a single cotton-top tamarin (L. Pastorello, pers. comm.). Individuals of the same sex are recommended for pairing.

 Within Group Aggression

Fighting within groups resulting in the removal of individuals is not atypical for cotton-top tamarins. Typically, in family groups aggression tends to be directed toward natal rather than breeding individuals; aggressors are usually the same-sex parent or siblings (McGrew & McLuckie, 1986). Fights between same-sex twins have been observed, although the majority of aggression in stable family groups tends to be between the eldest male siblings (S. Evans, pers. comm.; A. Savage, pers. comm.). Most of the aggression between individuals begins slowly, but has been known to rapidly escalate and culminate in death. The age at which aggression and resulting eviction of natal individuals from the group occurs is variable and unpredictable.

Aggression between Eldest Male Siblings is most common in stable family groups. As group size increases due to high birth rates in this species, fighting between the two eldest male siblings is common. Interestingly, the rest of the group members appear to ignore the tension between the two animals. Low levels of aggression are most common initially, (displacement at the food dish, rough play, chasing, mounting) but generally escalates to one individual dominating the other. The subordinate sibling emits submissive vocalizations constantly (squawks, see Cleveland & Snowdon, 1982) and typically avoids contact with the dominant sibling. The victim may also show fearful behavior upon being approached by the dominant individual and often stays lower dm normal in the exhibit. It is recommended that the sibling harassing the subordinate sibling be removed from the family when this is observed before any severe fighting develops. Do not attempt to reintroduce this animal to the group.

Aggression between Father and Male Offspring-occurs in stable family groups, but is most often observed when there has been some change in the environment. Moving animals to new exhibits or introducing another species to residents can often result in group disruption. Fathers can behave very aggressively toward their offspring, often resulting in severe fighting. The offspring should be removed and no attempts to reintroduce the offspring to the group should be made.

Aggression between Females is relatively rare and most commonly occurs when there is a disruption in the environment (see above). Daughters have been observed to challenge their mothers (mounting, harassing, displacing) but, unless the mother is old or impaired, she will usually defend her position in the group. Daughters should be removed from the family group only if the mother is becoming aggressive. Most daughters can live in stable family groups for many years. Evictions of sons are much more frequent than daughters in most captive cotton-top tamarin groups.

Social Behavior

There have been extensive studies of the behavior of cotton-top tamarins in captivity and in most recently in the wild. Studies have shown that most captive cotton-top tamarins live in monogamous pairs. Newly formed pairs of cotton-top tamarin show increased affiliative behavior and are observed to engage in sexual activity more frequently than do established breeding pairs (French et al., 1984; Savage et al., 1988; Tardif, 1984a; Widowski et al., 1990). This increase in affiliative behavior occuring when the female was removed from the family and paired with a male appears to be important in establishing the pair bond in this species. However, as the duration of the pair bond increases, affiliative behavior and scent marking decreases (Savage et al., 1988). This decrease has been attributed to the addition of offspring to the group. Established breeding pairs often spend less time in affiliative behavior with one another and direct more of their attention toward their offspring (Savage et al., 1988). Nonetheless, the pair bond appears to be strong in these animals as intruders are attacked (French & Snowdon, 1981) and territorial displays between cages in large colony rooms of tamarins are frequent when visual contact between groups is allowed.

Scent Marking Cotton-top tamarins have highly developed anogenital and suprapubic scent glands (see French & Cleveland, 1984 for a complete review). Both males and females are observed to scent mark, however, females scent mark significantly more than their male counterparts. The function of scent marking has been widely debated. Studies have suggested that scent marking does have a communicatory function in callitrichids (see Epple, 1975; Ziegler & Bercovitch, 1990). Rates of scent marking differ between cycling and non-cycling females. Newly paired cotton-top tamarin females showed a dramatic increase in rates of scent marking, rates much higher than those observed when females lived with their families or in isolation (French et al., 1984; Savage et al., 1988). Savage et al., (1 988) and Widowski et al., (I 990) found a positive correlation between estrogen activity and frequency of scent marking. Increases in scent marking paralleled increased in estrogen activity, with the highest frequency of scent marking occurring when the female was cycling. However, the highest frequency of scent marking occurred when the female was paired with a male.

The increase in scent marking also parallels the similar changes in the apparent amount of sebum produced by the scent glands. Although the total area of the scent gland does not change, it appears to produce more sebum after the female was removed from her family and paired with a male (French, 1982; Savage et al., 1989). Thus, it appears that the scent glands are fully developed in females by the age of 20 months but require the stimulation of elevated levels of estrogen to produce sebum and a darkening of the pigment (Savage et al., 1989).

Vocalizations Cotton-top tamarins have a highly developed vocal repertoire (Cleveland & Snowdon, 1982) with at least 38 distinct vocalizations. They have specific vocalizations for alarm, food, levels of aggression, and submission. Tamarins possess a rudimentary syntax and grammar and it has been suggested that infant cotton-top tamarins go through a "babbling" or practice stage as they learn the appropriate vocalizations (C. Snowdon, pers. comm.). A copy of the "Vocal Repertoire of the Cotton-top Tamarin" is available on loan from the Wisconsin Regional Primate Research Center Library (1223 Capitol Ct., Madison, WI 537151299 phone 608 263 3512).