17 December 2010

Kokako successfully anchored in ‘safe’ forest

This blog post was written by postgraduate student Anna Reuleaux as part of the course, Research Methods in Ecology (Ecol608).

North Island kokako are an endangered New Zealand forest species known for their beautiful song. In the past conservationists have translocated these birds from mainland areas to managed islands and succeeded in establishing new populations. These safe kokako havens were predominantly literal islands surrounded by water but also used have been islands of suitable forest in a ‘sea’ of grassland or farmland. The advantage of these islands is the guarantee that the birds will stay in the area that has been prepared for them by predator control. But how do you get birds to stay in a managed area if it is situated in continuous forest without any boundaries to stop dispersal?

Laura Molles and her colleagues attempted such a translocation to a managed area surrounded by continuous forest: Ngapukeriki is located in the Bay of Plenty on the North Island of New Zealand. The conservationists decided to use social attraction in order to encourage the kokakos to stay in the target area after release. For the kokako the presence of resident individuals indicates that they are likely to find the right habitat conditions, food resources and potential mates in the vicinity.

But what if there are no resident kokako yet in the target area? One answer is to trick the birds, giving them the impression that there are plenty of other kokako around. In this case three social attractants were used simultaneously: 1. releasing many birds at the same time; 2. keeping a pair of kokako in an aviary at the release site and 3. using playback of kokako song as ‘acoustic anchor’.

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Acoustic anchoring is the most exciting one of these tactics as it had never before been used in translocations of terrestrial birds. Recordings for the playback were made in the source population so that the translocated birds could be exposed to the song of their former neighbours, singing and calling in their familiar ‘dialect’. Three kokako held in the aviary at the release site responded positively to a trial playback.

Eighteen kokako were released in July and August 2005. After the release the playback was broadcasted for one and a half hours every morning from speakers near the release site. Most of the released birds visited the area of the playback at least once, some of them repeatedly. On several occasions kokako approached and counter-sang with the playback speakers.

All this is good evidence that acoustic anchoring is likely to have contributed significantly to the success of this translocation. On the other hand this study was not designed to prove the effectiveness of acoustic anchoring on its own but to find out if the combination of the three social attractants would lead to a successful establishment of a population. The re-introduction of kokako to Ngapukeriki can definitely be regarded as a success as the first young already fledged in 2006. “And every year since, the kokako of Ngapukeriki have bred successfully and the population continues to grow” says Laura.

The researchers also pointed out that acoustic anchoring is also worth investigating for the translocation of other terrestrial species. Laura Molles and her team have already put that into practice in a translocation of Tui to Banks Peninsula in 2009. The acoustic anchoring technique has also been trialled on robins, whiteheads and in two further kokako translocation projects.

This article is based on:

Molles, L.E., Calcott, A., Peters, D., Delamare, G., Hudson, J.D., Innes, J., Flux, I., Waas, J. 2009. 'Acoustic anchoring' and the successful translocation of North Island kokako (Callaeas cinerea wilsoni) to a mainland management site within continuous forest. Notornis 55(2): 57–68.


Photos from kokakorecovery.org.nz with kind permission from Laura Molles.

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