We are interested in re-examining the long standing debate over what have been the evolutionary drivers of acoustic signals in mammals.  There are two dominant theories; either that the physical constraint of body size or alternatively that the environment that an animal lives within has driven the divergence of vocalisation frequencies. We are taking a comparative approach and using a model selection approach to identify what are the best supported drivers of  the acoustic features of mammalian vocalisations.  We are examining the vocalizations of 193 different mammalian species across the globe and from the terrestrial and aquatic environments.