Whistles characteristics of common dolphins (Delphinus sp.)in the Hauraki Gulf, New Zealand

Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation and social relevance. Vocalisations of free-ranging common dolphins (Delphinus sp) have not previously been described from New Zealand waters. Herein, I present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, Auckland between February 2008 and May 2009, during surveys from the tour boat Dolphin Explorer. Data were collected from 28 independent dolphin groups using PZ-1A hydrophone and MZ-NH700 digital audio disk. Recordings were analysed using Raven Pro 1.3 and whistles classified into seven contours containing 29 subtypes. A total of 105.1 minutes of recordings were collected involving 11,715 whistles. Vocalisations of New Zealand common dolphins spanned 3.2 to 23.00 kHz, with most whistles occurring between 11 and 13 kHz. The shortest and longest whistles recorded were 0.01 and 4.00 s (mean = 0.27, SD = 0.32), respectively. Of the twelve whistle types recorded, 82% have previously been recorded within U.K populations. Additional contours, apparently specific to New Zealand Delphinus were also identified. Of the 2,663 whistles analysed, downsweeps (35.9%) were the most frequent whistle type, followed by upsweeps (28.5%), constant (16.4%) and sine (7.0%) contours. Concave and convex contours were least observed within the New Zealand population, accounting for just 6.1% each. Of all the whistle types identified in Hauraki Gulf common dolphins, the least modulated subtypes were the most prevalent. Data presented here offer a first insight into the whistle characteristics of New Zealand common dolphins. Comparsions with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Inter-population differences suggest behaviour and the local environment likely play a role in shaping the vocal repertoire of this species.