Ontogeny

In most otarrid species, pups learn their mother’s vocal signal before their first separation, that is, within a few days. Studies performed in California sea lions showed that even pups less than 2 weeks old are capable of discriminating their mothers’ calls from those of other females with an accuracy rivaling that of the adult female. Pups were also shown to play a more active role in reunions as they got older, i.e. pups actively moved towards the mother (Gisiner et al., 1991). In Australian sea lion pups, however, newborn pups were not found to respond differentially to the call of their mother versus the call of a foreign sea lion, suggesting that vocal recognition development occurs later. This disparity is hypothesized to be the result of variance in colony density, pup movements, and natal site fidelit, reducing selective pressures on call recognition. Alternatively, another sensory system may be used for recognition in the early stage of life. Pups are weaned at about 10 months old, and at the age of 5 sea lions reach sexual maturity (Charrier et al., 2009).

The ontogeny of an adult female’s ability to recognize her offspring immediately after parturition has not been tested.  However, given the rapid development of pup mobility and the frequent mother-pup vocal interaction during this period, it is probable that recognition by mothers develops relatively quickly. Since a pup needs to be able to recognize its mother when she comes back from foraging, its response to her voice should have developed before her first departure. In fact, responses to playback tests have shown that pups react vocally to any female’s call after birth but after 2-5 days they can respond specifically to their mother’s voice.  In addition, studies have shown that the departure date of the female depends on the establishment of the pup’s response that is, the mother will not leave on a foraging trip until the pup has developed the ability to recognize her voice (Charrier et al., 2001).

Research on northern fur seals, a species belonging to the otariid family, has shown the following:

1. Recognition is not affected by pup development from birth to weaning

2. Mothers recognize calls of their pups from the previous season

3. Pups recognized their mother’s vocalizations recorded one year earlier

4. 4-year old primparous females still recognized their mother’s vocalizations despite a low probability of contact since weaning.

Although long term affiliative associations between mother and offspring have been shown in captivity, such a behavior has yet to be shown in natural populations. These findings suggest that a form of permanent vocal/auditory imprinting occurs between mother and offspring shortly after birth, and further, demonstrates the potential for complex interactions among individuals over long time-frames. (Charrier et al., 2003)