Abstract:
A signature whistle type is a learned, individually distinctive whistle type in a dolphin’s acoustic repertoire that broadcasts
the identity of the whistle owner. The acquisition and use of signature whistles indicates complex cognitive functioning that
requires wider investigation in wild dolphin populations. Here we identify signature whistle types from a population of
approximately 100 wild common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, and describe signature
whistle occurrence, acoustic parameters and temporal production. A catalogue of 43 repeatedly emitted whistle types
(REWTs) was generated by analysing 79 hrs of acoustic recordings. From this, 28 signature whistle types were identified
using a method based on the temporal patterns in whistle sequences. A visual classification task conducted by 5 naı¨ve
judges showed high levels of agreement in classification of whistles (Fleiss-Kappa statistic, k = 0.848, Z = 55.3, P,0.001) and
supported our categorisation. Signature whistle structure remained stable over time and location, with most types (82%)
recorded in 2 or more years, and 4 identified at Walvis Bay and a second field site approximately 450 km away. Whistle
acoustic parameters were consistent with those of signature whistles documented in Sarasota Bay (Florida, USA). We
provide evidence of possible two-voice signature whistle production by a common bottlenose dolphin. Although signature
whistle types have potential use as a marker for studying individual habitat use, we only identified approximately 28% of
those from the Walvis Bay population, despite considerable recording effort. We found that signature whistle type diversity
was higher in larger dolphin groups and groups with calves present. This is the first study describing signature whistles in a
wild free-ranging T. truncatus population inhabiting African waters and it provides a baseline on which more in depth
behavioural studies can be based.
