The reproductive success of the beluga whale is critical for a species facing extinction in its endangered Cook Inlet, Alaska population. To date, little is known about the mating behavior of these whales in wild populations. On the other hand, observations of beluga whales in human care allow researchers to better understand many aspects of their daily lives and life histories that are difficult to assess in wild populations. Thus far, a catalog of socio-sexual behavior has been established based on observations of belugas; however, the developmental trajectory of socio-sexual behavior is not well-understood. The present study explored how socio-sexual behavior developed in beluga whales under human care by recording the behavior of 5 belugas between ages 4 through 10 and coding for socio-sexual behavior. Overall, the presence of young male conspecifics was the most influential predictor of whether or not the subjects engaged in socio-sexual behavior. The subjects of the present study were also more likely to be involved in socio-sexual behavior as they matured and were more likely to be involved if they were male. In contrast, the presence of environmental enrichment devices (EEDs) did not affect the prevalence of socio-sexual behavior. Additionally, specific socio-sexual behaviors, including horizontal s-postures and pelvic thrusts, increased in prevalence throughout development. This information is important for the management of beluga whale populations both in human care and in the wild. Understanding that social group composition may contribute to the development of socio-sexual behavior, which in turn may influence the reproductive success of beluga whales, lays the ground work for future research of socio-sexual behavior in wild belugas. Furthermore, because socio-sexual behavior composes a relatively large portion of a beluga’s activity budget and the majority of the time spent socializing, it is likely crucial for social bonding and well-being in belugas
