Evaluating the Abundance of Prey Animals for the Oriental White Stork in Spring and Summer in the Western Part of Echizen City, Fukui Prefecture

27 Mar Evaluating the Abundance of Prey Animals for the Oriental White Stork in Spring and Summer in the Western Part of Echizen City, Fukui Prefecture

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Abstract

越前市西部地域（以下，越前市）におけるコウノトリの餌動物の個体数密度を調査し，2012年に人工給餌に依存せず雛を巣立たせたペアが営巣した豊岡市福田（以下，福田）の結果と比較した．春期（ 6 月）の水田での調査では，越前市の餌動物の個体数密度は，福田のコウノトリの採餌が確認された水田と同水準であった．夏期（ 8 月）の水田畦での調査では，越前市の餌動物の個体数密度は福田よりも少なかった．夏期の餌動物の個体数密 度に影響する局所的要因として，平均植生高と植被率，水田側の水面の存在が抽出された．越前市白山地区の飼育ケージ周辺の水田面積は，福田とほぼ同じ水準であった．以上の結果から，少なくとも餌動物の個体数密度に関しては，春期の越前市の水田には，コウノトリが利用可能な水準の餌動物が生息していると評価できる．一方夏期には，越前市の水田畦における餌動物密度は福田より少ないものの，畦草管理の強度や頻度を抑制したり， 退避溝を増設したりするなどの水田管理上の配慮によって向上する余地があると考えられる．

English Abstract

We investigated the abundance of prey animals for the Oriental White Stork, Ciconia boycia , in the western part of Echizen city (hereafter, ECHIZEN), Fukui prefecture, and compared the results with those of a similar investigation conducted in 2012 at Fukuda, Toyooka city, Hyogo prefecture (hereafter, FUKUDA), where a pair of C. boycia raised two fledglings being completely independent of artificial feeding. In spring (June 2013), abundance of aquatic prey in the paddy field of ECHIZEN was comparable to that of the particular paddy field selected by foraging C. boycia in FUKUDA. In summer (August 2013), density of terrestrial prey inhabiting the dykes of paddy field was less in ECHIZEN than in FUKUDA. Environmental factors that significantly influence prey abundance in the dykes of paddy fields included microhabitat variables such as height and coverage of grassy vegetation and the presence or absence of water in the paddy field. The expanse of the paddy fields surrounding the breeding cage in the Shirayama area in ECHIZEN is similar to that in FUKUDA. Thus, paddy fields in ECHIZEN would supply prey animals as abundantly as those in FUKUDA, at least during the spring. Although prey abundance in the dykes of paddy fields is currently lesser in ECHIZEN than in FUKUDA in the summer, farm ma gement practices such as reducing the intensity and frequency of mowing, and/or increasing water-filled catchment ditches in paddy fields have a potential to enhance prey abundance during midsummer drought caused by artificial drai ge.