Long-term tracking reveals a dynamic crocodylian social system

Animal social systems are inherently dynamic, with individuals moderating how they associate with conspecifics according to spatiotemporal shifts in population demography and resource availability. Understanding such variation is important not only to further our knowledge of a species' ecology but also to gain insights into the factors influencing the evolution of animal social systems. Using a 10-year acoustic telemetry data set containing the movements and co-occurrences of 166 tagged individuals, we investigated how time of year, individual sex and maturity status affect the social organization and connectivity of a wild population of estuarine crocodiles, Crocodylus porosus. We found that our tagged population of crocodiles displayed social structure, where individuals segregated spatially into distinct communities along 120 km of river and estuary. The social organization and structure of these communities were temporally dynamic, with association rates and the connectedness of individuals peaking during the dry season before disintegrating prior to the onset of the wet season. The formation of communities was found to coincide with an increase in the frequency of co-occurrence events between mature and mature–immature dyads prior to the onset of the mating season. Together these findings indicate that estuarine crocodiles have a structured social system, where the proximity to the mating season and an individual's maturity status dictate how they associate with conspecifics.