Journal Article

Effectiveness of vole control by owls in apple orchards

Azuma, Nobuyuki, Watanabe, Kana, Inada, Aya, Sato, Sho, Murano, Chie, Kudo, Seiya, Kasahara, Satoe

2019

Overview

Biological pest control is gaining greater acceptance as an important part of integrated pest management for sustainable agriculture. However, knowledge regarding biological control of rodent pests is limited, and its effectiveness in temperate areas has not been quantified. In traditional Japanese apple orchards, the Ural owl Strix uralensis breeds in tree hollows and preys on the Japanese field vole Microtus montebelli, a native pest species that can harm fruit production. In this study, we hypothesised that the Ural owl, a generalist predator, can act as a biological control agent by reducing vole densities in temperate orchards. To quantify the pest control effects of breeding Ural owls, we first analysed the diet of individual owls nesting in apple tree hollows. Second, we installed nest boxes in orchards to attract breeding owl pairs and collected data on vole population changes around owl nests to compare with control areas. The population changes were analysed using a generalised linear mixed model to assess the effect of breeding owls within their breeding territory. The model considered seasonal fluctuations in vole population size as well as surrounding land‐use. We also examined vole populations around the owl nests in April, and the distance between nests and forested areas, to determine if these variables influenced nest site selection. Voles were the primary prey of Ural owls breeding in orchards and the owls reduced vole populations within their estimated breeding territories by 63% (±SE: 53%–70%) compared with the predicted density without owls. Owls preferred to nest in orchards with higher vole population densities in April. Our findings also indicate that higher occupancy rates are possible by distributing nest boxes based on Ural owl breeding territory size (306 m radius circle in our study). Synthesis and applications. As breeding Ural owls provide significant pest control effects within their breeding territories, the reintroduction of breeding Ural owl pairs within orchards would contribute to rodent pest control. Promoting the reproduction of native raptors in agricultural areas can be an option for developing integrated pest management while simultaneously maintaining regional biodiversity. Foreign Language 天敵を利用して,農作物を加害する有害生物を抑制する生物的防除手法は,総合的有害生物管理 (IPM; Integrated Pest Management) の主要な柱の一つとして注目を集めつつある.しかしダニや昆虫等を対象にした生物的防除の研究は幅広く行われている一方,同じく主要な加害動物である小型哺乳類の生物的防除の研究は種や地域に限定的で,温帯地域における小型哺乳類の生物的防除の研究は少ない.そこで本研究では,近年まで日本の伝統的なリンゴ園で繁殖していたフクロウStrix uralensisに注目した.フクロウは小型哺乳類の個体数を抑制するとされるジェネラリスト型捕食者である.繁殖期にはリンゴの樹洞に営巣し,害獣であるハタネズミMicrotus montebelliを餌として捕食するが,近年は栽培方法の変化に伴い果樹園内の樹洞が減少し,フクロウの営巣も減少している.本研究では,リンゴ園で繁殖するフクロウがハタネズミの個体数に与える効果を定量的に把握し,フクロウによる生物的防除の可能性を検証することとした. フクロウの効果を定量化するため,まずリンゴの樹洞で繁殖するフクロウが雛に給餌する餌生物を調査した.次にリンゴ園に巣箱を設置してフクロウの繁殖を誘致し,営巣地と営巣地以外のリンゴ園間で,ハタネズミ個体数の季節変化を比較した.個体数解析には一般化線形混合モデルを用い,個体数の基本的な季節変動や周辺の土地利用の影響を考慮したうえで,フクロウの繁殖がハタネズミ個体数に与えた影響を抽出した.またフクロウの営巣場所の選好性を見るため,巣箱周辺の4月のハタネズミ生息密度と,巣箱から森林までの距離を調査し,営巣した巣箱と営巣しなかった巣箱間で比較した. 調査の結果,リンゴ園で繁殖するフクロウが育雛期に巣に運び込んだ餌生物の8割以上がハタネズミであった.またフクロウの繁殖によって,巣周辺のハタネズミ密度は,フクロウの繁殖がなかった場合と比較して63% (± SE: 53%–70%) 減少していた.さらに,フクロウは,4月時点でのハタネズミ生息密度が高い園地を選択的に繁殖に利用していた.また調査期間中の繁殖結果より,フクロウの繁殖期のなわばり面積 (本研究対象地では半径306 mの円) を考慮して巣箱架設を行うことで,巣箱利用率を高められることも示唆された. Synthesis and applications. リンゴ園で繁殖するフクロウは,営巣地周辺のハタネズミ個体数を有意に低減していることが明らかになった.減少しているフクロウの繁殖を巣箱によって再誘致することは,リンゴ園における害獣管理に有効であると考えられる.農地における在来の猛禽類の繁殖支援は,総合的有害生物管理の有効な手段になりうると同時に,地域の生物多様性保全にも貢献できるだろう. As breeding Ural owls provide significant pest control effects within their breeding territories, the reintroduction of breeding Ural owl pairs within orchards would contribute to rodent pest control. Promoting the reproduction of native raptors in agricultural areas can be an option for developing integrated pest management while simultaneously maintaining regional biodiversity.

• Publisher: Wiley,Blackwell Publishing Ltd
• Subject: Agricultural practices / Animal behavior / Apples / Biodiversity / Biological control / biological control agents / biological pest control / Birds of prey / Boxes / Breeding / Crop production / diet / Foreign languages / forests / Fruit trees / fruits / generalist predator / Indigenous species / Integrated pest management / Japanese field vole / Land use / microtine population / Microtus / Microtus montebelli / Nest boxes / Nesting / nesting sites / Nests / Occupancy / Orchards / Owls / Pest control / Pests / Population / Population changes / Population density / population dynamics / Population number / population size / Populations / predator–prey / Prey / prey species / Regional development / Reintroduction / RESEARCH ARTICLE / Rodent control / rodent pest / Rodents / seasonal variation / Seasonal variations / Site selection / statistical models / Strix / Strix uralensis / Sustainable agriculture / Synthesis / temperate zones / territoriality / Territory / tree cavities / Ural owl / voles