The initial confrontations of 33 previously unfamiliar pairs of common marmosets were observed. Four types of pairs were used (alpha males/alpha females; alpha males/subdominant females; alpha females/subdominant males; subdominant males/sub-dominant females). Each dyad was tested in five different experimental conditions: (1) isolation of both individuals from their families, unilateral encounters in which either the (2) male’s or the (3) female’s family was visible to the dyad through a one-way screen, and interactive encounters in which either the (4) male’s or the (5) female’s family was present behind a wire screen. Pairs which included alpha females exhibited no affiliative, practically no sexual, but high levels of aggressive behaviors. Pairs which included subdominant females exhibited affiliative, high levels of sexual, and practically no aggressive behaviors. Behavior was reduced qualitatively as well as quantitatively with increasing presence of the families. Possible functional aspects of the results are discussed.

Prolactin has long been known to play a significant role in maternal care. When behavioral endocrinologists began to examine the endocrinology of fatherhood, prolactin was also found to be connected with paternal care in fish, birds, and mammals including primates.

Duets from a total of 6 female and 6 male titi monkeys (Callicebus cupreus) were analysed in order to provide an in-depth analysis of the duet structure, to investigate whether duets are pair specific and to examine whether duets of newly formed pairs differ from those of established pairs. Callicebus duets are composed of alternately uttered male and female contributions. Duets were pair specific as a result of a summation of individual attributes of the two mates rather than due to unidirectional or reciprocal song adaptation by mates. The two examined newly formed pairs produced species-typical duets from the first day on, but their duets showed greater variability in sequence durations than those of established pairs.

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