Dolphins do not know international borders. The Guyana dolphins (Sotalia guianensis) and Bottlenose dolphins (Tursiops truncatus) that inhabit the waters of Changuinola (Panama) also use the coastal waters of Gandoca (Costa Rica). This is the only resident population of Guyana dolphins known for both countries. Like their neighbors from Bocas, these two dolphin populations live in small and relatively isolated populations. Although dolphins are known to form mixed species groups all over the world, their association is short-lived, but in the waters of Changuinola and Gandoca both Guyana and Bottlenose dolphins mixed daily a unique behavior that has been rarely described in other parts of the world. Why do they mix? and what prompts these associations? are some of the questions we are trying to answer. Here is a summary of what we know so far
Social network and factors promoting mixing behavior
Mixed groups in Changuinola-Gandoca are mainly observed when the animals are socializing. However, not always socializing implies 'nice' behaviors, in fact, our observations indicate that sometimes Guyana dolphins are harass constantly by the much larger bottlenose dolphins. Despite the cost of these aggressive behaviors, Guyana dolphins are sometimes observed promoting such mixed associations. We are interested in studying the proximate and ultimate causes of this behavior. In collaboration with Dr. Jennifer Lewis we will be starting a project along these lines next year 2013.
Interspecific acoustic communication project
Guyana dolphins are among the dolphin species that emit communication signals within the ultrasonic range. Our most recent work indicates that these two species of dolphins may change their signal when found together. The reasons of these changes are largely unknown and so we will be starting a project with acoustic tags that allow us to determine what species (and individuals) are emitting sounds.
May-Collado, L.J. 2013. Guyana dolphins (Sotalia guianensis) from Costa Rica emit whistles that vary with surface behaviours. Journal of the the Acoustic Society of America, Express Letters, 134: in press
May-Collado, L. J. 2010. Changes in whistle structure of two dolphin species during interspecific associations. Ethology. 116:1065-1074.
May-Collado, L.J. and D. Wartzok. 2009. A characterization of Guyana dolphin (Sotalia guianensis) whistles from Costa Rica: The importance of broadband recording systems. Journal of the Acoustical Society of America. 125 (2): 1202-1213