Dear Colleagues, On behalf of myself and my co-authors, we are excited to share the following paper: *Vocal repertoire, micro-geographical variation and within-species acoustic partitioning in a highly colonial pinniped, the Cape fur seal* Mathilde Martin, Tess Gridley, Simon Elwen, Isabelle Charrier *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. Royal Society Open Science 8:202241 https://doi.org/10.1098/rsos.202241 Please feel free to contact me with any questions! Best regards, -- *Mathilde MARTIN* PhD Student Acoustic Communications Team, Department Cognition & Network Neuroscience NeuroPSI - Paris-Saclay Institute of Neuroscience 151 rue de la Rotonde, 91400 Saclay, FRANCE https://neuropsi.cnrs.fr Tel: +33 (0)1 69 82 63 56 Email: mathilde.martin@universite-paris-saclay.fr Website: https://mathildemartin-research.com/