The low-frequency vocal repertoire of adult African dwarf crocodiles

Abstract

Acoustic techniques are rapidly becoming powerful tools for species monitoring and biodiversity assessment. These methods can be particularly appropriate for forest-dwelling crocodiles which are difficult to survey visually. However, basic vocal-repertoire data is lacking for many of the poorly known species. Here, we used passive acoustic recorders to capture 97 spontaneous vocal signals from a pair of captive adult African dwarf crocodiles (Osteolaemus tetraspis). We catalogued their acoustic repertoire and compared the calls recorded in captivity with 201 suspected wild O. tetraspis calls recorded in Gabon to determine whether the wild calls belonged to the same species. Captive and wild crocodiles produced the same four types of calls, not previously identified in other crocodylids. Short, low-frequency “drums” (31±12 Hz), longer, low-frequency “rumbles” (40 ± 14 Hz), as well as higher frequency “moos” (299 ± 133 Hz) and “gusts” (219 ± 108 Hz). Our results provide reference for species identification and support implementation of acoustic-based methods for African dwarf crocodile monitoring and conservation assessment. The data can further contribute to landscape-wide biodiversity monitoring and counter-poaching activities, as well as improving our understanding of crocodilian ecology and behaviour.