Biomedical subjects
Publications and source records attributed to M Biben.
This is the first published report of twinning in a squirrel monkey (genus Saimiri). The mother survived but the twins, both male and close to full term, were stillborn.
Three groups of squirrel monkeys, containing 1-3 infants (N = 7) and 4 adult females each, were observed weekly for the first 12 weeks of the infants' lives. Infants received approximately 100 vocalizations, mostly "caregiver" calls, per waking hour from their mothers and the other adult females with whom they were housed (allomothers). Mothers vocalized very little to their own infants during the first few weeks of life, when infants remain on the mother's back full-time. Instead, allomothers (who were often carrying their own dependent infants) vocalized copiously to others' very young infants. Infants responded vocally to these allomaternal caregiver calls as early as Day 1 but were less responsive to mothers. When infants began leaving the mothers' backs, mothers' rates of calling increased five-fold as they used caregiver calls to retrieve separated infants. Early vocalizing to infants involves them in their first social exchanges and is probably performed by allomothers rather than mothers because the infant rides dorsally in this genus.
This study investigates the occurrence and structure of the caregiver call, a form of communication in squirrel monkeys that is almost exclusively infant-directed. Caregiver calls exhibit variability in several acoustic features, most notably pitch range and contour, which are significantly associated with particular contexts of infant care; e.g., nursing or retrieval. The use of caregiver calls by squirrel monkeys is compared to the use of motherese (infant-directed speech) by humans. The possible functional and motivational basis for specific acoustic variables in the caregiver call is discussed.
Vocalizations occurring during play bouts were studied in 2 pairs of young male squirrel monkeys. Two main call types, one having four variants, are described. Vocalization rate varied with the type of ongoing behavior and with play bout duration, an association considered to be indicative of motivation to play. Structural differences also varied with bout duration and longer bouts had longer and more complex calls. In addition to providing direct information about motivation, vocalizations may have a metacommunicative function in alerting adult group members (not play partners) to the presence of playful activity.