Contact and recruit – the importance of acoustic communication in the foraging strategy of a flightless seabird

While foraging, seabirds use various cues to navigate, including other predators to signal the presence of inconspicuous prey. Transfers of information have been conceptualised in flying seabirds as local enhancement and foraging networks, with visual signals used over a few kilometres. In flightless seabirds, however, visual signals are limited at the sea surface. We hypothesised that these species are likely to use acoustic signals as a primary form of communication. We analysed the at-sea acoustic communication process in a flightless seabird, the African penguin ( Spheniscus demersus , Linnaeus, 1758), from the production of signals (acoustic structure of calls) to their reception (behavioural response to calls playbacks), to experimentally assess their biological function. Penguins produced calls and responded to calls in all foraging contexts (commuting, searching, after feeding), although they responded more when searching for food. Our results revealed two functions of sea-surface calls: a contact function (i.e. eliciting a vocal response of conspecifics) and a recruitment function (drawing their approach). We suggest that vocal communication is regularly used be penguins to maintain contacts at sea over a few hundred meters, to form groups and to possibly recruit them to foraging grounds thus facilitating group foraging. The importance of acoustic communication in African penguins reveals their sensitivity to noise pollution. This risk must be urgently considered in the conservation strategies of this Critically Endangered species.