Ivan ( Janez ) Regen ( called Johann Regen ) ( December 9 , 1868 â `` July 27 , 1947 ) , was a Slovenian biologist . He is best known for his studies in bioacoustics , the science of hearing and communicating . Ivan ( Janez ) Regen ( known also as Johann Regen ) ( December 9 , 1868 â `` July 27 , 1947 ) was a Slovenian biologist , best known for his studies in the field of bioacoustics .