Nesting Facilitation of Medium-sized Birds of Prey

27 Mar Nesting Facilitation of Medium-sized Birds of Prey

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Abstract

猛禽類の巣の土台となりそうな太枝がない若齢針葉樹に，人工巣を設置することで中型猛禽類の営巣を誘導できるか，試みた。その結果，オオタカとトビ，それぞれ一つがいが営巣を行った。オオタカは２羽の巣立ち雛を育てることに成功した。トビは育雛期になって巣を放棄したが，原因は山菜採りによる撹乱の可能性が疑われた。オオタカは前年に自ら構築した自然巣が近くにあったにもかかわらず，人工巣を利用した。トビが利用した人工巣は，もともとトビを含む中型猛禽類の営巣がみられなかった地域に設置されたものだった。これらの結果は，若齢や間伐遅れのために太枝が発達していない針葉樹でも，人工的に中型猛禽類の営巣を誘導することが可能であることを示した。この技術を利用すれば，営巣適木がない森林を営巣適地に変えることが可能で，結果として生息地域拡大も期待できる。

English Abstract

We have tried to facilitate nesting of medium-sized birds of prey by placing artificial nests on young conifers without thick branches that could support their nests. A pair of the northern goshawk Accipiter gentilis and a pair of the black kite Milvus migrans nested on the artificial nests. The goshawks raised two fledglings successfully. The black kites abandoned the nest during brooding possibly due to the disturbance by people searching for edible wild plants. The goshawks used the artificial nest although their tural nest in the previous year was nearby. The artificial nest used by the black kites was located in the area where the nesting of medium-sized birds of prey, including the black kite, had not previously been observed. The results indicate that it is possible to artificially facilitate nesting of medium-sized birds of prey even on the conifers that have not developed thick branches, which may be simply because of the age or the delay of thinning. The application of this technique could render the forests without trees suitable for nesting, possibly leading to the expansion of their habitat.