Same-sex socio-sexual interactions among male narwhal

Abstract

Abstract: Same-sex socio-sexual behavior is seemingly ubiquitous across the animal kingdom. Although difficult to observe in wild cetaceans, aerial imagery using drones has drastically improved our ability to document such behaviors. In 2017, off northern Baffin Island, Canada, a group of eight adult male narwhals were recorded engaging in same-sex socio-sexual behavior. To describe and analyse the recorded behaviors, we developed an ethogram using behavioral analysis software. All eight individuals engaged in close physical contact and presented their ventral side to at least one other whale; five were observed to have erections, and four of those five rubbed their genital area against at least one other male in the group. Possible explanations of same-sex socio-sexual behavior in animals include creating, maintaining or reinforcing social connections amongst peers, juveniles ‘practising’ to improve their success in future heterosexual (i.e., reproductive) encounters, or to increase or decrease intra-sexual aggression and conflict. Proximate and ultimate causes for the behavior of this group of narwhal remain uncertain, as females were observed nearby, the activity occurred outside of the mating season, and this group was composed of adults, based on tusk and body length. To our knowledge, this is the first documented case of same-sex behaviors amongst narwhal and raises the question of whether it is common amongst male individuals. Increased use of drones in behavioral research of this species, will likely address this latter question. Significance Statement: Same-sex sexual behavior would appear to contrast the evolutionary theory of natural selection. Presuming sex and reproduction are synonymous to achieve a reproductive advantage, individuals should prefer reproductive over non-reproductive sex, and opposite-sex over same-sex mates. Observing same-sex sexual behavior consequently begs the question, why, and opens the door to investigating what kind of social benefits may result from these activities. We documented sexual interactions between male narwhals, including reciprocity, and evaluated age class via tusk size. While this eliminated certain possible explanations, such as juvenile ‘practice’, gaps in our understanding remain. Little is known of narwhal sexual and social behavior, but these data reveal how age, or rank may influence these types of interactions, and begin to shed light on the proximate and ultimate causes behind same-sex socio-sexual behavior in this species.