Plasticity in the agonistic behaviour of male California sea lions, Zalophus californianus

Environmental conditions may influence mating behaviour in otariids breeding in areas with elevated temperatures and intense solar radiation. Although they have evolved morphological and physiological adaptations to prevent overheating while breeding on land, under extreme temperature conditions, they must adjust their behaviour in order to thermoregulate. The California sea lion mating system is based on male competition and displays that occur while defending their territories when females are present. We studied the agonistic behaviour of adult males at two breeding colonies in Mexico with contrasting environmental characteristics: Isla Santa Margarita (ISM) (Pacific coast) and Isla San Esteban (ISE) (Gulf of California). The goal of this study was to determine which variables influence where (i.e. on land or in the water) aggressive interactions between adult males occurred using logistic regression analysis. We analysed three scenarios: (1) both islands, (2) only ISM and (3) only ISE. The best model for the first scenario included the air temperature, density of females and type of aggression. The second scenario involved the density of females, and the third scenario included the rate of female interactions. Although the California sea lion mating strategy involves monopolizing critical resources, our results indicate that density of females and rate of female interactions have a significant impact on where male aggressive interactions occur. Our results highlight how changing environmental conditions affect the behavioural plasticity of this species' mating system. Most notably, males inhabiting high-temperature environments use the thermoregulatory strategy of defending territories adjacent to the coast while remaining immersed in the water. This strategy may result in decreased polygyny in the Gulf of California colonies relative to those on the Pacific coast.