Despite the fact that nonlinearities are present in the calls of a number of different species, their adaptive function has received little empirical investigation. Previous studies have demonstrated that playbacks of non- linear calls evoke a more extreme behavioural response and lead to an increase in responsiveness compared with control playbacks without non- linearities. Consequently, it has been suggested that nonlinearities might prevent receivers from habituating, by increasing the unpredictability of the call (‘unpredictability hypothesis’). In this study, we tested the unpre- dictability hypothesis, specifically whether nonlinearities prevent receiv- ers from habituating, by means of a playback experiment using meerkat (Suricata suricatta) alarm calls. We found that in meerkats, playbacks of naturally occurring nonlinear alarm calls take longer to habituate to than alarm calls without any nonlinear intrusions. These data provide impor- tant empirical support for the hypothesis that nonlinearities are not just an irrelevant by-product of the vocal production system, but indeed func- tion adaptively.