Vocalisations of the Marbled Frogmouth II: An Assessment of Vocal Individuality as a Potential Census Technique

Abstract

Using recorded vocalisations of Marbled Frog-mouths Podargus ocellatus from southern Queensland, an assessment was undertaken of the extent of vocal individuality and its potential as a census technique. The ‘Kerloo’, an apparently territorial vocalisation, was selected as being most likely to demonstrate individuality. Qualitative comparisons of spectrograms were abandoned due to the inability of workers to distinguish between birds. A detailed quantitative analysis employed 11 measures taken from on-screen spectrograms. Discriminant Function Analyses were able to separate almost all individuals reliably for both males and females. Three variables were of particular importance in the functions derived for both sexes: the duration of the Kerloo; the frequency range; and the number of elements included in a call. The ability of the technique to separate individual birds was high and its applicability to field studies appears possible provided workers are proficient with the analyses and that the behavioural context of the calls is appreciated.