Social interactions of the nocturnal primates are not well studied. One of the species for which social behavior is scarcely known is the Philippine tarsier (Tarsius [= Carlito] syrichta). We observed a reproducing pair of captive individuals over two mating seasons for two consecutive years. The tarsiers spent approximately 4% of their activity budget on social interactions; ca. 20% of time in 0-1 m proximity to each other; and shared sleeping sites for half of the study time. The majority of the animals' social interactions were peaceful: affiliative and sexual (83%), and the smallest component of the behavior was agonistic (17%). We witnessed two copulation events (one per estrus day), each lasting ca. 5 min, and both occurring just after waking. We revealed temporal - nightly and hourly - fluctuations in the frequency of social interactions, in the distances the individuals spent from each other and in the number of vocalizations. The results present the first assessment of the social behavior of the Philippine tarsier, much needed to improve the captive breeding management for this highly sensitive species threatened with extinction.
Keywords: Nocturnal primates; affiliation; aggression; captive breeding; mating.