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Can consistent individuality of voice be used to census the vulnerable Noisy Scrub-bird Atrichornis clamosus?

Berryman, Abby (2003) Can consistent individuality of voice be used to census the vulnerable Noisy Scrub-bird Atrichornis clamosus? Honours thesis, Murdoch University.

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The Noisy Scrub-bird Atrichornis clamosus is a secretive bird, seldom seen but often heard. Its song is loud and distinctive and can be heard up to 1.5km away on a still day. Noisy Scrub-birds are censused on an annual basis by mapping the locations of singing individuals (all assumed to be males). This study investigated the potential for the identification of individuals using consistent individuality of voice. It assessed the use of this method as a tool to calibrate current census techniques, as well as examining more general aspects of the singing behaviour of Noisy Scrub-birds, and develops a model to explain the observations.

Noisy Scrub-bird territorial song was recorded at Two Peoples Bay Nature Reserve from June 2002 to May 2003. At each of the 25 territories studied, the singing individual was found to use a repertoire of between 3 and 8 different song types at any one time. The size of the repertoire was generally larger during the breeding season (May-September) and about half the maximal size in the summer, non-breeding months. Generally, birds avoided repeating the same song type in immediate succession. However, outside the breeding season, repetition was more likely, probably due to the smaller repertoire size.

There was substantial song sharing amongst clusters of 2-7 neighbouring birds, deemed to comprise a song group. In some cases, there was entire repertoire overlap between some members of the group. Song groups were discrete, with neighbouring song groups having no song types in common. Often there were no acoustic or other barriers between neighbouring song groups and the distance between two members of the same song group could be greater than between two individuals in adjacent .song groups. Despite the similarity of shared songs, one song type shared between three individuals, when analysed in detail, did show significant differences between the renditions given by different individuals. Presumably this would be applicable to other song types as well. However, further analysis was not practicable due to the extremely time-consuming nature of the task, combined with the presence of repertoire change.

Repertoires changed with time as song types were modified, old song types were abandoned, and new song types were introduced. More than half of all song types in a repertoire could be replaced, or at least significantly modified, over a month, with complete repertoire renewal over 6 months. However, song groups remained cohesive over a year, with all group members changing their song types to maintain repertoires that were identical or nearly identical among all members.

The presence of song sharing, combined with repertoire change, meant that the initial proposal for identification of individual Noisy Scrub birds by voice is unlikely ever to be feasible.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Wooller, Ron
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