Time to put up or shut up

Abstract

. Vocalizing by natural-living harbour seals has been considered to be rare, limited primarily to aerial threats. A few studies on captive harbour seals, however, indicated that this species produced a wider variety of aerial vocalizations than was previously thought. The objective of this study was to determine whether adult male harbour seals in the wild vocalized under water during the breeding season and whether there was any variation in vocalizations between individuals. Underwater vocalizations of 10 males were tape-recorded at Point Lobos State Reserve, California during the spring and summer of 1991. Females did not vocalize except on land when they threatened other seals. Observational data was taken to identify the vocalizing seal and to determine whether other seals in the vicinity showed any reactions to the vocalizations. Five vocalization types were identified and analysed: grunt, groan, creak, bubbly growl and roar. There were significant differences between males with regard to the frequency measurements of the roars as well as to their entire acoustic displays but there was little intra-individual variation. It is suggested that underwater vocalizations are used in male-male competition and/or as reproductive advertisement displays to attract females.