How a pup identifies its mother in a colony of Antarctic fur seals [abstract]

T. Aubin, I. Charrier, N. Mathevon & P. Jouventin (2002). How a pup identifies its mother in a colony of Antarctic fur seals [abstract]. Bioacoustics, Volume 13 (2): 186

When returning to their breeding colony from a foraging trip at sea, mothers of Antarctic fur seals Arctocephalus gazella have to find and identify their own young among hundreds of pups. Before meeting and suckling can occur, both mothers and pups call to each other at a distance and then, coming into contact, exchange nose-sniffs. To investigate the way in which pups recognise their mothers acoustically, we carried out playback experiments in the field with different kinds of modified maternal calls. Frequencies (pitch, relative levels of harmonics), amplitude and frequency modulations (AM and FM of calls were modified using synthesis techniques. According to our tests, it appears that pups pay attention to the FM shape and to the spectral profile (pitch + relative levels of harmonics, i.e. timbre) of the call to identify their mothers. It appears also that finding mothers is a two stage process for pups. At long range (more than 20m), a maternal call broadcast repeatedly often attracts several pups. Our propagation tests suggest that, at this distance, pups can only analyse the FM shape of the signal and this would explain the misidentifications observed. At a shorter distance (about 8m), only the right pup (exceptionally two pups) replies to the playback.  In this case, it seems that pups can analyse simultaneously a combination of two acoustic parameters of the maternal call: the FM shape and the spectral profile. This combination improves the accuracy of the identification process. The final verification by scent made by the mother appears as an additional means to secure fully the identification of the right pup and to prevent extra nourishment of non-offspring.