The following paper is available at http://www.asmjournals.org/perlserv/?request=get-toc&issn=1545-1542 Journal of Mammalogy, 89(5):1229Ð1240, 2008 A COMPARISON OF BOTTLENOSE DOLPHIN WHISTLES IN THE ATLANTIC OCEAN: FACTORS PROMOTING WHISTLE VARIATION LAURA J. MAY-COLLADO* AND DOUGLAS WARTZOK George Mason University, Department of Environmental Science & Policy, MSN 5F2, 4400 University Drive, Fairfax, VA 22030, USA (LJM-C) Florida International University, Department of Environmental Science, 11200 SW 8th Street, Miami, FL 33199, USA (DW) Whistles are narrowband, frequency-modulated sounds produced by many cetaceans. Whistles are extensively studied in delphinids, where several factors have been proposed to explain between- and within-species variation. We examined factors associated with geographic variation in whistles of common bottlenose dolphins (Tursiops truncatus) by assessing the role of ambient noise, noise from boats, and sympatry with other dolphin species, and reviewing and comparing whistle structure across populations in the western and eastern Atlantic Ocean. Whistles of adjacent populations differed, particularly in frequency parameters. A combination of factors may contribute to microgeographic whistle variation, including differences in ambient noise levels (dolphins produced relatively higher frequency whistles in the noisiest habitat), and differences in number of boats present (when multiple boats were present, dolphins whistled with greater frequency modulation and whistles were higher in maximum frequency and longer than when a single boat was present). Whistles produced by adjacent populations were relatively similar in structure. However, for clearly separated populations, the distance between them did not relate directly to whistle structure. We propose that plasticity in bottlenose dolphin whistles facilitates adaptation to local and changing conditions of their habitat, thus promoting variation between populations at different geographic scales. Key words: ambient noise, boat traffic, Costa Rica, Panama, Sotalia, sympatry, Tursiops -- Laura J. May-Collado, Ph.D. Affiliate Assistant Professor Department of Environmental Science & Policy George Mason University Email: lmaycollado@gmail.com Personal Home Page: www.delphinids.com