Vigilance in Female Bottlenose Dolphins (<em>Tursiops sp.</em>) Before and After Calving

Abstract

Previous research has indicated that bottlenose dolphins alternate activity levels between hemispheres while at rest. This rest strategy allows dolphins to maintain continuous vigilance of their external environment. Dolphins in the care of humans exhibit different behaviors while presumably at rest, including floating at the surface, lying at the bottom, and swimming at very slow speeds in stereotyped patterns. Dolphin mothers in the care of humans have been reported to “not rest” and swim continuously for extended periods of time (weeks or even months) when their calves are first born. The current study examined the night-time rest patterns and vigilance of five female bottlenose dolphins before and after parturition. By differentiating between two types of resting behaviors (floating and slow swimming), we found that mothers altered their rest strategy depending on the parturition state. Floating was only observed at high levels preparturition. In contrast, mothers primarily exhibited active swims (a vigilant state) the first two weeks, post-parturition. The remaining six weeks were characterized by a steady increase in slow swimming (a resting, vigilance state). This change in swim behavior may be associated with neonatal development and may allow mothers to sustain high levels of vigilance for extended periods of time. The results of a behavioral test of vigilance indicated that the mothers also increased their vigilance level post-parturition. Mothers sustained their increased response rate over the eight-week post-parturition period, demonstrating that dolphin mothers maintain high levels of vigilance for an extended period of time.