The involvement of parents and siblings in infant care in similarly composed groups of common marmosets (Callithrix jacchus) and cotton-top tamarins (Saguinus oedipus) was compared during the infants' first 8 weeks of life. The results indicate an earlier infant independence in C. jacchus than in S. oedipus due primarily to a more frequent rejection of carried infants in C. jacchus. There was no species difference in extent of maternal involvment in carrying infants. However, S. oedipus fathers carried infants significantly more often during weeks 5-8 than did C. jacchus fathers. Siblings were generally more involved in infant care at an earlier infant age in C. jacchus than in S. oedipus.

Infant care behavior was examined for 35 litters of 23 different groups of captive cotton-top tamarins. The behavior of mothers and fathers was compared to determine the effects of infant number and helper presence on each parent and to determine whether parents differed in responsiveness to infants. For young infants (1-4 weeks), the contribution of fathers to infant carrying was negatively correlated with helpers' contribution; as helpers carried more, fathers carried less. In contrast, the mothers' contribution to infant carrying was unaffected by helper contribution. Mothers carried older infants (5-8 weeks) less than did fathers, regardless of infant number or helper contribution. Fathers and mothers were equally likely to retrieve a non-harassed infant; however, fathers were more likely than mothers to retrieve an infant being harassed. These results suggest that fathers are more responsive to infants than are mothers. Mothers may limit their involvement in infant care, as has been proposed by field results, due to an energetically demanding reproductive strategy.Marmoset Research Center, Oak Ridge Associated Universities, Oak Ridge, Tennessee

Infant‐care behavior patterns of captive cotton‐top tamarins were examined to assess factors defining participation by non‐reproductive helpers. The time spent carrying infants and characteristics of infant transfers were examined for 47 helpers in a total of 18 groups. We predicted that age, previous experience, and carrying opportunity would all affect participation of non‐reproductive helpers. Our results confirm that carrying by non‐reproductive helpers was related to age, with older helpers carrying more often. However, this difference declined with increasing infant age, suggesting that body size of the carrier was not the only factor determining participation in carrying. When observations were classified relative to type of interaction with infants, older juveniles were found to both investigate and harass infants more often than subadults or younger juveniles. There was no effect of gender on carrying. The carrying behavior of subadults was not affected by their previous experience; that is, subadults with no previous exposure to infants carried as often as those with previous experience. Inter‐individual variation among helpers was high; within 11 twin litters of helpers, one animal usually carried significantly more than the other.

Histological sections of colons from 69 tamarins (46 Saguinus oedipus and 23 Saguinus fuscicollis illigeri) and 27 marmosets (Callithrix jacchus) that died between 1979 and 1984 were examined for colitis. Evaluated biological factors were species, age at death, source of animals, manner of death, presence of colon cancer, and time after importation. Most normal colons were found in young animals (dead at less than 1 years of age). Nearly all (approximately 96%) animals had colitis; 70-80% of most groups were graded as chronic colitis. Usually, one grade adequately described the condition of the entire colon. The strongest observed correlation of factors (P less than 0.05) was between acute colitis and colon cancer in S. oedipus. A higher percentage of S. oedipus had acute colitis than did the other two species. When colitis incidence data were adjusted for S. oedipus with colon cancer, there were no observed species differences between colons of colony-born and imported animals nor between those that died naturally and those that were euthanized. In an additional group of 18 S. oedipus that were imported in 1975, acute colitis was found in 60% of those dying immediately after importation (less than 1 year of colony age) and those that survived greater than 3 years. At this time, no causative agent has been identified in marmoset colitis.

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