Behavior of Infant Chimpanzees During the Night in the First 4 Months of Life: Smiling and Suckling in Relation to Behavioral State

Yuu Mizuno, Hideko Takeshita, Tetsuro Matsuzawa
2006 Infancy  
This article reports the behavior of 3 newborn chimpanzees in the first 4 months of life, reared by their mothers and living in a community of 14 chimpanzees in a seminatural enriched environment. We focused on spontaneous activity during the night partly because sleeping behavior constitutes an essential part of the infants' activity. Observation during the night also had the advantage of keeping the influence of the mothers' activity as well as the environmental stimulation constant
more » ... constant throughout the observation period. We report several interesting findings. Behavioral states defined through overt features such as open or closed eyes were variable during the night, with the rapid eye movement ( E M ) and non-REM sleep patterns alternating much as they do in human infants. Although crying is one of the distinctive behavioral states in the case of human infants, the chimpanzee infants did not cry like humans. Suckling behavior was often accompanied by open eyes until the end of the first 2 months. Thereafter, suckling with the eyes closed became more prominent. Although there were no explicit stimuli, the newborns showed neonatal smiling with the eyes closed during REM sleep periods. However, neonatal smiling disappeared within the ~~~~~ ~ ~~ ~~~~ Correspondence should be addressed to
doi:10.1207/s15327078in0902_7 fatcat:x3yli5yazjcwbjfqpos6avzh5i