Mother Vocal Recognition in Antarctic Fur Seal Arctocephalus gazella Pups: A Two-Step Process.

Thierry Aubin,Isabelle Charrier,Pierre Jouventin,Daniel E Crocker

doi:10.1371/journal.pone.0134513

Abstract

In otariids, mother’s recognition by pups is essential to their survival since females nurse exclusively their own young and can be very aggressive towards non-kin. Antarctic fur seal, Arctocephalus gazella, come ashore to breed and form dense colonies. During the 4-month lactation period, females alternate foraging trips at sea with suckling period ashore. On each return to the colony, females and pups first use vocalizations to find each other among several hundred conspecifics and olfaction is used as a final check. Such vocal identification has to be highly efficient. In this present study, we investigated the components of the individual vocal signature used by pups to identify their mothers by performing playback experiments on pups with synthetic signals. We thus tested the efficiency of this individual vocal signature by performing propagation tests and by testing pups at different playback distances. Pups use both amplitude and frequency modulations to identify their mother’s voice, as well as the energy spectrum. Propagation tests showed that frequency modulations propagated reliably up to 64m, whereas amplitude modulations and spectral content greatly were highly degraded for distances over 8m. Playback on pups at different distances suggested that the individual identification is a two-step process: at long range, pups identified first the frequency modulation pattern of their mother’s calls, and other components of the vocal signature at closer range. The individual vocal recognition system developed by Antarctic fur seals is well adapted to face the main constraint of finding kin in a crowd.

Highlights

Otariids are social animals that use vocal signals in several social contexts such as territorial and female defense, aggressive behavior and mother-pup identification
All were strongly correlated to PC1, with latency to call (LC) and latency to look (LL) negatively correlated to PC1 (-0.85 and -0.82 respectively, 0.91 for number of emitted calls (NC))
Playback experiments with synthetic signals clearly show that several acoustic parameters are used by Antarctic fur seal (AFS) pups to identify their mother’s voice

Summary

Introduction

Otariids are social animals that use vocal signals in several social contexts such as territorial and female defense, aggressive behavior and mother-pup identification (for a review see [1]). Recognition of mothers by pups is essential to pup survival as females exclusively nurse their own young [4] and can be very aggressive towards non-kin [5,6].This is exacerbated by the repeated and frequent maternal absences during the course of lactation: otariid mothers alternate foraging trips to sea (1–20 days depending on species) with bouts of suckling ashore (1– 5 days). For these reasons, an efficient individual recognition process is needed in order for a pup to safely relocate its mother in the crowded colony. Vocal recognition between mother and young has been observed and experimentally demonstrated in several pinnipeds species (see [1] for review, [12,13,14,15]), the fine acoustic mechanisms involved in individual vocal identification are only known in two species, the Subantarctic fur seal, Arctocephalus tropicalis [16,17] and the Australian sea lion, Neophoca cinerea [12,18]

Methods

Results

Conclusion