Vocalisations of the Great Spotted Kiwi (Apteryx haastii): an assessment of vocal individuality
|Keywords:||vocal individuality; Apteryx haastii; Hawdon Valley; whistle call; fundamental frequency; autonomous acoustic recording; acoustic monitoring; call rate; vocal dimorphism|
|Full text PDF:||http://hdl.handle.net/10182/6339|
Kiwi (Apteryx spp.) vocalisations are routinely used as part of a nationwide monitoring programme in which call-rate is used to infer population density. The ability to individually identify kiwi would drastically improve the accuracy and quality of monitoring programmes. One potential avennue to achieve this is through acoustic identification. In many vocally active species, vocalisations have been shown to encode information about the identity of the caller (vocal individuality). This has proven extremely useful in monitoring rare, nocturnal and cryptic bird species. In this study, vocal individuality was assessed with regard to a population of great spotted kiwi (Apteryx haastii) residing in the Hawdon Valley, Canterbury, New Zealand. Acoustic recorders were installed near the breeding den sites of seven great spotted kiwi pairs between November 2012 and March 2013. In total 303 whistle vocalisations were recorded during this time. A range of temporal and spectral parameters were measured from the highest quality recordings. These measurements were taken at a whole call and individual syllable level. Call parameters were; number of syllables, syllable rate and syllable duration. Syllable parameters were; minimum frequency (Hz), maximum frequency (Hz), bandwidth (Hz), duration (sec) and peak frequency (Hz). These variables were used to describe and classify calls using one-way repeated measures ANOVAs and stepwise discriminant function analysis. Male and female syllables are sexually dimorphic, however, the pattern of temporal and spectral variation within calls is consistent between sexes. Discriminant function analysis indicated that great spotted kiwi vocalisations were highly individualised. Male individuals were were classified with an accuracy of 95.7% on the basis of seven parameters. Females were classified with an accuracy of 90% on the basis of five call parameters. In both analyses spectral parameters were shown to be most important for individual discrimination. This is the highest degree of vocal individuality in Apteryx species reported to date. Such a high degree of individuality indicates that great spotted kiwi vocalisations could be utilised for individual identification purposes. The next step is to assess the temporal stability of this phenomenon.