SEX DIFFERENCE IN SIGNATURE WHISTLE PRODUCTION OF FREE-RANGING BOTTLE-NOSED DOLPHINS, TURSIOPS-TRUNCATUS

Signature whistles of 42 free-ranging bottlenose dolphin calves were c ompared to those of their mothers. Humans judged their similarity by i nspection of spectrograms. There was a sex difference in the tendency of calves to produce whistles similar to or different from those of th eir mothers; most female calves produced whistles that were different from those of their mothers, whereas male calves were more likely to p roduce whistles that were similar to those of their mothers. Because m atrilineally related females associate together and use signature whis tles to establish and/or maintain contact with their calves, there may be a selective pressure for females to produce whistles that are dist inct from those of their mothers. There may be fewer constraints gover ning whistle development in males, with the result that some males pro duce whistles similar to those of their mothers and others do not.