The orchard guardian: pest vole control by owls

Following the recently published article, Effectiveness of vole control by owls in apple orchards, Chie Murano highlights the vital role predators such as Ural owls play in protecting farmers’ produce from pests.  

Voles are one of the world’s major pests. For the past few decades, Japanese farmers, especially apple producers have suffered from escalating levels of apple tree damage caused by the Japanese field vole Microtus montebell. Young dwarf apple trees, which are developed for intensive productions, are particularly fragile to vole damages. With increasingly stringent regulations on chemicals and rodenticides, there is a growing demand for alternatives to help manage and reduce damage caused by voles.

A dwarf apple tree damaged by voles. Voles gnaw tree trunks during the snow season. © Chie Murano.

We hypothesized that one of causes behind the increasing damage by voles might correlate to the decrease presence of the predator, Ural owls trix Uralensis in orchards. According to older apple farmers,  owls breeding in the hollows of apple trees was a common sight until the end of 20th Century. Many apple farmers affectionately viewed owls as the guardian angels of orchards. With the gradual adoption of intensified production scheme in the region, old trees with hollows suitable for owl nesting had been removed and replaced with younger dwarf trees. Nowadays farmers rarely find owls nesting in apple orchards. It is well known that avian predators have an impact on small rodents’ population dynamics, but the effect of the native owl in orchards has never been scientifically investigated.

We aimed to quantify the vole control effect by breeding owls in orchards. As a first step, we investigated the prey items fed to owlets by monitoring owl nests in apple tree hollows found in orchards during between 2003 and2007. Then as a second step, we installed 60 nest boxes in orchards to attract owls during breeding seasons from 2015 to 2017 and measured the vole population changes around owl nests with live-trappings and compared to the basic vole population dynamics in control area.

Owlets just after fledging, holding a vole provided from a parent owl. © Satoru Chiba.

The farmers’ observation was correct. Our study revealed that voles were the primary prey of Ural owls breeding in orchards and that vole populations around owl nests reduced drastically during the owl nesting period. The pest control effect of breeding owls in orchards has been scientifically verified.

The vole population changes from April to November within owl breeding territory (straight lines) compared to the control; out of breeding territory (dash-dotted lines) in 2016 and 2017.

Our nest box experiment illuminates the ecosystem service that apple productions have previously relied upon but that has not been well documented or acknowledged. We are grateful that we could undertake this study and bring to light the benefits of an accidental coexistence of Ural owls and apple orchards before it disappears completely. Understanding our place in the ecosystem should be the best way to develop an effective, sustainable pest management scheme.

Read the full article, Effectiveness of vole control by owls in apple orchards in Journal of Applied Ecology.

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