This study aimed to expand on previous efforts to evaluate the ontogeny of echolocation in Atlantic bottlenose dolphins (Tursiops truncatus). Data consisted of echolocation recordings and concurrent behavioral observations taken from one calf in 2000 and from five additional dolphin calves and their mothers in 2002 housed at the U.S. Naval facility in San Diego, CA. A total of 361 echolocation click train samples from calves were recorded weekly over the first 6 months of the calves’ lives. The earliest calf echolocation train was recorded at 22 days postpartum and the number of echolocation attempts from calves increased steadily with age. Calf echolocation trains increased in duration and the number of clicks per train with age while train density (clicks/sec) and interclick interval values remained more consistent. Calves swimming independent of their mothers produced more click trains, especially when multiple calves were present in the social grouping. When considering these results in the context of possible maturation of a calf’s melon physiology, it seems very likely that the first two months of life are critical for the development of echolocation and related behaviors. While the first click train recorded in this sample was approximately 3 weeks of age by two different calves, it is possible that dolphin calves may innately produce functional sonar clicks immediately after birth, which were not captured in the current study. Future research will need to investigate this possibility using more controlled conditions and a better understanding of the anatomy and physiology of the sonar system of neonates as well as the possible role of the mother in echolocation development.
Further insights into postpartum signature whistle use in bottlenose dolphins (Tursiops truncatus)
