Field Observations of Same-sex Non-reproductive Mounts in Adult Male Philippine Long-tailed Macaques (Macaca fascicularis)

Non-reproductive sexual behaviors have been reported in many different animal taxa, including non-human primates (NHPs). One of the Philippine NHPs that exhibits non-reproductive sexual behaviors, specifically same-sex sexual behaviors (SSSBs), is the long-tailed macaque (LTM). We observed SSSBs during our ecological and behavioral surveys of wild LTMs in Brgy. New Israel, Makilala, Philippines. We recorded multiple non-reproductive mounts (NRMs) among adult males with two detailed observations of anogenital contacts and ejaculations of the mounters. There are several hypotheses that may explain why these sexual behaviors are displayed by macaques (e.g. dominance assertion, social tension reduction, and inaccessibility of females); however, our observations could not be completely explained by these hypotheses due to our limited number of records. We recommend that more thorough research should be conducted to increase our understanding of the possible reasons behind the SSSBs of LTMs.