Attention grabbing in red deer sexual calls.

Identifying the respective functions of distinct call types is an important step towards understanding the diversification of mammal vocal repertoires. Red deer (Cervus elaphus) stags give two distinct types of roars during the rut, termed 'common roars' and 'harsh roars'. This study tests the hypothesis that harsh roars function to raise and maintain female attention to calling males. To this end, we examined the response of female red deer to playback sequences of common roar bouts including a bout of harsh roars midway through the sequence. We found that females not only substantially increased their attention to the bout of harsh roars but also then maintained overall higher attention levels to subsequent common roar bouts. Our results suggest that the specific acoustic characteristics of male red deer harsh roar bouts may have evolved to engage and maintain the attention of female receivers during the breeding season. More generally, they indicate a possible evolutionary path for the diversification of male sexual vocal repertoires.