Behavioral rhythms of gibbons on Hall's island

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Abstract
A group of gibbons (Hylobates lar) has been maintained in the seminatural, designed environment of Hall island, Bermuda, since 1970, demonstrating the feasability of long term, experimental studies of animals instrumented with intracerebral electrodes and a shoulder harness to carry radio stimulators and telemetric units for recording of mobility. Observations of spontaneous behavior were synchronized using 5 sec units, broadcast to experimenters in the field. The following conclusions are derived from our study: (1) Daytime gibbon mobility showed a periodicity related to basic biological clocks and not to mutual behavioral influences. (2) Periodicities were consistent for the same animal on different days and homogeneous intervals, validating observations made during relatively brief periods. (3) Caudate nucleus stimulation produced inhibition while central gray stimulation induced escape. Neither effect modified spontaneous rhythms. (4) Behavioral categories such as SITS, HANGS, and SWINGS remained within specific limits of occurrence on different days but showed clear oscillations, suggesting the existence of ultradian rhythms. CLIMBS had one daily peak while FORAGES had two peaks. (5) Biological mechanisms regulating cyclic activity may be similar in the Laboratory and in open field situations. (6) We propose a mathematical treatment for the analysis of behavioral data, considering the animal as a stochastic generator of random sequences. The model provides a description of basic states versus time facilitating a probabilistic prediction of primate social behavior with greater accuracy than in the past.

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