Tactile Contact Exchanges Between Dolphins: Self-rubbing versus Inter-individual Contact in Three Species from Three Geographies

Abstract

Self-rubbing and social-rubbing (pectoral fin contact between dolphin pairs) were compared for observations conducted on three dolphin study groups: wild dolphin groups in The Bahamas and around Mikura Island, Japan, and a third group of captive dolphins at the Roatan Institute of Marine Sciences, Roatan, Honduras. A primary aim of this research was to determine whether self-rubbing and social pectoral fin rubbing served overlapping functions. Self-rubbing rates were nearly identical between the three study sites, suggesting that site-specific differences (e.g., environmental conditions, substrate, presence of rocks or coral, social grouping) do not affect the rates at which dolphins rub their bodies against non-dolphin objects. The function of self-rubbing is not entirely clear, and likely involves a combination of factors (e.g., play, pleasure), with functions such as hygiene possibly being shared by both self-rubbing and social-rubbing. Rubbing behavior in general (e.g., rates, body parts used) were similar at all three sites for all three species, suggesting that rubbing is an evolutionarily conserved behavior for delphinid species. Still, subtle and individually distinct differences were documented among our study groups with respect to how often and with whom dolphins exchanged pectoral fin contact or engaged in self-rubbing. Site-specific social pressures and predation risks, as well as individual personality might play a role with respect to the expression of an individual’s observed rubbing behavior.