Vocal repertoire, micro-geographical variation and within-species acoustic partitioning in a highly colonial pinniped, the Cape fur seal

Abstract

Communication is fundamental for the survival of animal species as signals are involved in many social interactions (mate selection, parental care, collective behaviours). The acoustic channel is an important modality used by birds and mammals to reliably exchange information among individuals. In group-living species, the propagation of vocal signals is limited due to the density of individuals and the background noise. Vocal exchanges are, therefore, challenging. This study is the first investigation into the acoustic communication system of the Cape fur seal (CFS), one of the most colonial mammals with breeding colonies of hundreds of thousands of individuals. We described the acoustic features and social function of five in-air call types from data collected at two colonies. Intra-species variations in these vocalizations highlight a potential ability to convey information about the age and/or sex of the emitter. Using two classification methods, we found that the five call types have distinguishable frequency features and occupy distinct acoustic niches indicating acoustic partitioning in the repertoire. The CFS vocalizations appear to contain characteristics advantageous for discrimination among individuals, which could enhance social interactions in their noisy and confusing acoustic environment. This study provides a basis for our understanding of the CFS acoustic communication system.

Temporal patterns in Cape fur seal (Arctocephalus pusillus pusillus) mother and pup attraction calls

“…Upon return, mothers and pups must find each other in dense colonies, and facilitate reunions using mostly vocal and olfactory cues (see review in iNsley et al, 2003). Mothers produce individually specific, stereotyped and loud 'pup attraction calls ' (PAC;iNsley 1992;PhilliPs & sTirliNG 2000;charrier et al 2003;marTiN et al 2021a) to find their young, confirming this recognition by olfactory cues (PhilliPs 2003;PiTcher et al 2011). Similarly, a pup looking for its mother actively searches the colony while producing 'female attraction calls ' (FAC;GisiNer & schusTermaN 1991;iNsley 1992;marTiN et al 2021a).…”

“…Mothers produce individually specific, stereotyped and loud 'pup attraction calls ' (PAC;iNsley 1992;PhilliPs & sTirliNG 2000;charrier et al 2003;marTiN et al 2021a) to find their young, confirming this recognition by olfactory cues (PhilliPs 2003;PiTcher et al 2011). Similarly, a pup looking for its mother actively searches the colony while producing 'female attraction calls ' (FAC;GisiNer & schusTermaN 1991;iNsley 1992;marTiN et al 2021a). Otariid pups learn to recognise their mother's vocalisations within days (e.g., Trillmich 1981;charrier et al 2001;PiTcher et al 2010), and females recognise their young in as little as a few hours (Trillmich 1981).…”

“…Here, we explore the temporal properties and rhythmic structure of attraction calls produced by the Cape fur seal, the only pinniped resident on the southern African coastline. Cape fur seals live in large, dense colonies throughout their range (kirkmaN et al 2013), and display a vocal repertoire typical of Otariids, including individually specific attraction calls produced by mothers and pups (marTiN et al 2021a(marTiN et al , 2021b. Cape fur seal pups produce series of stereotyped, high-pitched bleats facilitating reunion with their mothers (FAC;marTiN et al 2021amarTiN et al , 2021b.…”

“…Cape fur seals live in large, dense colonies throughout their range (kirkmaN et al 2013), and display a vocal repertoire typical of Otariids, including individually specific attraction calls produced by mothers and pups (marTiN et al 2021a(marTiN et al , 2021b. Cape fur seal pups produce series of stereotyped, high-pitched bleats facilitating reunion with their mothers (FAC;marTiN et al 2021amarTiN et al , 2021b. Similarly, mothers produce highly stereotyped calls to communicate with their pups at long or short distances (PAC;marTiN et al 2021amarTiN et al , 2021b.…”

“…Cape fur seal pups produce series of stereotyped, high-pitched bleats facilitating reunion with their mothers (FAC;marTiN et al 2021amarTiN et al , 2021b. Similarly, mothers produce highly stereotyped calls to communicate with their pups at long or short distances (PAC;marTiN et al 2021amarTiN et al , 2021b. They have excellent visual timing abilities (heiNrich et al 2020), which suggests a cognitive ability to keep and/or adjust rhythm.…”