CALF INSPECTIONS OF FISH CATCHES IN BOTTLENOSE DOLPHINS (TURSIOPS SP): OPPORTUNITIES FOR OBLIQUE SOCIAL LEARNING?

摘要

In recent years, the study of social learning and culture in wild cetaceans has visibly increased (Rendell and Whitehead 2001, Mann and Sargeant 2003, Krutzen et al. 2005). Some of the best evidence for some type of social learning in wild cetaceans comes from studies of vocal traditions in killer whales (Deecke et al. 2000, Yurk et al. 2002), song change in humpback whales (Noad et al. 2000), coda dialects in sperm whales (Rendell and Whitehead 2005), whistle convergence in bottlenose dolphins (Smolker and Pepper 1999, Watwood et al. 2004), and foraging behaviors in bottlenose dolphins (Mann and Sargeant 2003, Sargeant et al. 2005). The mechanisms (e.g., local enhancement, imitation) of social transmission have received very little attention, largely because this requires well-controlled experiments, compounded further by the difficulties in studying marine mammals. In a broader sense, determining whether transmission is vertical (parent to offspring), oblique (older to younger), or horizontal (laterally to peers or similar age classes), even without precise determination of mechanisms, offers insights into the ecological and social demands of a species. For example, horizontal transmission of song types in humpback whales is consistent with theproposed competitive function of song (Noad et al. 2000, Cerchio et al. 2001), and the context of pod-specific calls in killer whales suggests that calls promote cohesiveness (Miller et al. 2004). To date, our work on Shark Bay bottlenose dolphins (Tursiops sp.) suggests that vertical transmission of foraging types from mother to calf are commonplace (Mann and Sargeant 2003), but other forms of transmission may also occur (Sargeant et al. 2005). We argue that habitat heterogeneity and bisexual philopatry favors vertical transmission, especially for daughters who, more than sons, maintain a range similar to the mother's (Kriitzen et al. 2004). Forexample, sponge carrying, where dolphins use marine sponges on their rostra to aid in finding prey, is transmitted through matrilines almost exclusively (Krutzen et al. 2005). Here, we present evidence suggesting that calves seek exposure to prey caught by older non-mother individuals, but the converse is not true. Older individuals show little interest in what younger dolphins catch.