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Ornithological Science
Abstract
Abstract
Approximately one-third of all conservation translocations have failed to establish a self-sustaining population. Despite this historically low success rate, reintroduction is increasingly used in species recovery programmes in accordance with IUCN guidelines. Two commonly used methods of reintroduction involve ‘hard’ or ‘soft’ releases. A ‘hard’ release means immediate release from captivity into the wild, whereas ‘soft’ release involves individuals being kept for a period at a pre-release site and/or an extended period under care at the release site. In general, in recent reintroduction programmes, soft release is preferred over hard release because studies have shown that soft release can increase translocation success by encouraging animals to stay near the release point thereby utilizing supplementary food and delaying dispersal. The Crested Ibis Nipponia nippon used to be widespread in Japan, but became extinct in the wild during the early 1980s. In order to re-establish a wild population, a reintroduction programme has been implemented on Sado Island since 2003. Ten ibises were hard-released in 2008, and 20 were soft-released in 2009. In this paper, we quantify the differences in post-release movements by comparing the results of 2008 and 2009 releases, to determine whether release methods influence post-release behaviour. Linear mixed-effects modelling indicates that the post-release movements of birds varied depending on their gender, style of release, and season. In the reintroduction programme for the Crested Ibis on Sado Island, Japan, soft release appears to encourage birds to remain near the release site and to form a flock immediately after release.
This study resulted from collaboration with Sado Ranger Office of the Ministry of the Environment, Japan, with some of the data being provided by that office. Research was supported financially by the Environment Research and Technology Development Fund (4-1302) of the Ministry of the Environment, Japan, and by Grant-in-Aid for Scientific Research (B) No. 21310149 of the Japan Society for the Promotion of Science. We thank several anonymous reviewers, Dr Mark Brazil and Dr Phillip Seddon for constructive comments on the manuscript. We also thank Ms C. Koshida and Ms T. Mitsui for preparing individual information on the released birds. Finally, we would like to thank all members of the Toki Monitoring Team who supported our fieldwork on Sado Island.
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