Limited previous evidence suggests that killer whales ( Orcinus orca ) are capable of vocal production learning. However, vocal contextual learning has not been studied, nor the factors promoting learning. Vocalizations were collected from three killer whales with a history of exposure to bottlenose dolphins ( Tursiops truncatus ) and compared with data from seven killer whales held with conspecifics and nine bottlenose dolphins. The three whales' repertoires were distinguishable by a higher proportion of click trains and whistles. Time-domain features of click trains were intermediate between those of whales held with conspecifics and dolphins. These differences provided evidence for contextual learning. One killer whale spontaneously learned to produce artificial chirps taught to dolphins; acoustic features fell within the range of inter-individual differences among the dolphins. This whale also produced whistles similar to a stereotyped whistle produced by one dolphin. Thus, results provide further support for vocal production learning and show that killer whales are capable of contextual learning. That killer whales produce similar repertoires when associated with another species suggests substantial vocal plasticity and motivation for vocal conformity with social associates.

ACKNOWLEDGMENTS

We would like to dedicate this paper to Mike Owren, whose sad death prevented him from seeing the improvements in this paper based on his editorial advice. SeaWorld Animal Training and electronic services personnel assisted with data collection and facilitated audio and video recordings, as did Mike Muraco and his staff at Six Flags Discovery Kingdom. We are grateful to Duncan McGehee and Charles Greenlaw at BAE Systems for inventing an economical and effective method for localizing callers over long periods. Sam Denes prepared the statistical analyses in R. Dr. Judy St. Leger and Dr. Pam Yochem provided valuable comments. We thank our dedicated HSWRI staff and interns, particularly Jennifer Keating, Eri Suzuki, and Caitlin Scully. Study procedures were authorized by SeaWorld and Six Flags Discovery Kingdom. The Hubbs-SeaWorld Research Institute (HSWRI) Animal Care and Use Committee reviewed and approved the research protocols. J.L.C. and W.B.M. received support from the University of San Diego (USD), the Hannon Foundation (J.L.C.), and the Stephen Sullivan Memorial Scholarship Fund (W.B.M.). Both were graduate students in the Department of Marine and Environmental Studies at USD. The study was also supported by HSWRI and SeaWorld Entertainment.