Individual variation in nursing vocalizations of Hawaiian monk seal pups, Monachus schauinslandi (Phocidae, Pinnipedia), and lack of maternal recognition
Vocalizations of individual Hawaiian monk seal pups, Monachus schauinslandi, do not have unique attributes that enable females to recognize their own offspring. Despite low aggregation density during pupping, aggressive encounters are common between females with pups. Fostering is prevalent and may reflect confusion over the identity of pups following aggressive encounters between females. All pup vocalizations were simple in structure and contained true harmonics. The coefficients of variation revealed considerable variance in vocalization structure within pups. Controlling for age, multivariate analyses of variance revealed significant differences among pups in vocalization attributes. Significant developmental changes occurred in vocalization structure for some pups but not for others. Discriminant function analysis suggested that it would be difficult for females to distinguish between the vocalizations of pups. The results of experiments conducted in the field showed that females did not discriminate between filial and alien pups by voice. In addition, females tended not to foster pups that had vocalizations similar to those of their own offspring. Thus, females seem to be unable to recognize their pups by voice. The apparent lack of vocal recognition of pups may contribute to the high frequency of fostering in this species.