Mother-Offspring vocal recognition in northern fur seals is mutual but asymmetrical

During the 4-month period of offspring dependence, northern fur seal, Callorhinus ursinus, mothers and pups use a well-developed multimodal recognition ability to routinely find one another within large and dense breeding aggregations. I studied the vocal/auditory aspect of this ability to look at operational differences between the two members of a recognition dyad. If parent-offspring conflict theory is applied to animal communication behaviour, we should expect unequal selective forces acting on parents and offspring. In northern fur seal maternal recognition dyads, I expected pups to expend more energy in the reunion process because they carry the greater burden of a failed reunion. Furthermore, in terms of signal detection theory, pups should have a lower rejection threshold (lower bias) than mothers. To address these questions, I conducted vocal playback experiments and behavioural observations on a natural population of northern fur seals in the Pribilof Islands, Alaska, U.S.A. Although playback results support mutual vocal recognition, pups were both more vocally responsive and made more recognition errors (i.e. false alarms). Behavioural observations, including search time, distance travelled, signalling behaviour and contact with nonoffspring show that pups expend more effort in the reunion process. These findings are consistent with expectations and begin to quantify how selection pressure on recognition behaviour can vary at different stages of development. (C) 2001 The Association for the study of Animal Behaviour.