A Rescued Young Red-footed Booby Sula Sula Released After a Year of Captivity

27 Mar A Rescued Young Red-footed Booby Sula Sula Released After a Year of Captivity

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Abstract

2008 年 8 月 29 日に北海道で保護されたアカアシカツオドリSula sula の若鳥は，12 月 17日に生息域に近い西表島へ移送され，2009 年 9 月 4 日に野生復帰した．この約 20 日前の 8 月 14 日から，海況の比較的安定した日を選んで合計 12 日間のソフトリリースを実施した．飛翔時には小型船舶で追跡し，着水後の羽衣への海水浸透によって飛び立てなくなった場合には保護回収して飼育場所に戻すことを繰り返した．浮遊休息中の頻繁な水浴びにより羽衣の撥水性が回復し，同時に飛翔距離や海域滞在時間が徐々に増加した．これらのことから，保護された海鳥類を海洋生活に復帰させるには撥水性や飛翔力の回復の確認が重要であることが示唆された．

English Abstract

A young red-footed Booby Sula sula was rescued in Hokkaido, northern Japan on 29 August 2008 and was released on 4 September 2009 on Iriomote Island, southernmost Japan closer to its tural habitat. The individual was estimated to be two years old at the time of rescue, based on grey-brown mottles on the head and neck, and the uniformly dark brown coloration of the upperparts of the wings. Those mottles disappeared and the white morphing of wings and back increased the following summer. The appropriate body mass of the individual was estimated at 1100 g, and the amount of food was adjusted to 10% of the body mass measured in the early morning. Soft-release was carried out for a total of 12 days from 14 August to 4 September 2009. We followed the flying booby by boat and recaptured it at the point where it could no longer fly. During the period of soft-release, the water repellency of the plumage was restored through repeated bathing while floating on the surface, and flight range and time spent at sea increased. It is
suggested that the release process of rescued seabirds requires at least a number of days, allowing for the recovery of water repellency and capacity for flight. In addition, it is generally assumed that the probability of their survival after release would be low, without undergoing a similar release process.