Territorial animals commonly display lower levels of aggression towards familiar neighbours in familiar locations than towards neighbours in unfamiliar locations and towards unfamiliar individuals. A combination of acoustic signals and spatial cues mediates this form of social recognition in a variety of animals, including the North American bullfrog, Rana catesbeiana. In this study, we conducted two field playback experiments to investigate the perceptual basis of neighbour-stranger discrimination in bullfrogs. In a discrimination test following habituation training, a change of 10% in the fundamental frequency or 180° in the broadcast location of a synthetic bullfrog advertisement call elicited significant recovery of habituated aggressive responses. Hence, male bullfrogs can learn about an individually distinct property of acoustic signals and the signal's location of origin by repeatedly hearing the signal from a particular location. This study represents the first direct test of the hypothesis that territorial residents can learn about a specific property of a neighbour's acoustic signals and the location from which these are normally produced as a result of repeated exposures to the signal. We suggest that reduced aggression between territorial neighbours could be partially mediated by habituation to a neighbour's signals and location in bullfrogs.
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We are extremely grateful to Matthew Dyer, Kellee Blackwell, Alexandra Singer, and especially Chris Bowling for assistance in conducting playback tests. We also thank Don Martin, Jeff Koppleman, and the Missouri Department of Conservation for access to the Little Dixie Conservation Area. Josh Schwartz provided the program for synthesizing calls and technical assistance with the playback set-up. Haven Wiley, Philip Stoddard and Vince Marshall provided helpful comments on previous versions of the manuscript. This research was approved by the University of Missouri IACUC (#2944). M.A.B. was supported by an NSF Graduate Research Fellowship, an NSF Doctoral Dissertation Improvement Grant, and a Sigma-Xi Grant-in-Aid of Research. H.C.G. was supported by an NSF grant IBN 9507394 and an NIMH Research Scientist Award. The research presented here was further evaluated and approved by the Animal Behavior Society’s Animal Care Committee on 8 August 2001.