Drones, dry ice may help prevent damage caused by great cormorants(カワウ対策にドローン一役 高所の巣にドライアイス)

A group of great cormorants rests in the tree on the shore of Lake Inawashiro.Photos courtesy of the Fukushima prefecture government.(ドローンで空撮した猪苗代湖岸のカワウ。木の上に集団で巣を作り生息している=4月24日撮影(県提供))

 The Fukushima prefectural government is conducting a demonstration project using drones to control the reproduction of great cormorants. Great cormorants are colonial nesting birds that are prone to eating large amounts of freshwater fish, causing as much as 200 yen-300 million yen in damage to marine resources a year. Found all over Japan, the species' population has increased in recent years and damage to trees caused by their dung has also been a problem. As a result, urgent countermeasures are needed.
 In the project, dry ice is being dropped via drones into the birds' nests because they have a habit of nesting in high places. Doing so will cool their eggs and keep them from hatching. The prefectural government will verify the effects over several years and aims to make the results available throughout the prefecture.


 The project started in April on the shores of Lake Inawashiro, where groups of great cormorants build their nests. A private firm responsible for countermeasures to damage caused by animals was commissioned to conduct a monthly survey of the cormorants through the use of drones. About 5 million yen for related expenses has been included in the initial budget for this fiscal year.
 So far, dozens of birds have been observed in five conducted surveys. After the great cormorants finish laying eggs in March next year, dry ice will be dropped into their nests to observe the effects on hatching.


 Removing the birds with guns is difficult because of the safety risk it poses for residents if nests are found in places such as riverside urban areas or on lakeshores facing major roads. Expectations are for the demonstration project are high, because it can be carried out in residential areas.
 According to the prefectural government, there was a precedent in Yamanashi Prefecture where dry ice was used to tackle the issue. When dry ice was manually placed into a nest located in a shrub, a fixed effect of hatching suppression was observed. However, dealing with nests in high places where people were unable to reach, remained unsolved.
 "Through the use of drones, we can efficiently place dry ice in high places," an official at the Nature Conservation Division of the prefectural government said. "We hope to have a method established through this project to reduce [the amount of] damage."


 According to the prefectural government, 1,000 to 1,500 great cormorants are believed to live in the prefecture. Numbers of freshwater fish such as sweetfish, Japanese dace and carp, which have been bred and released by fisheries cooperatives in various parts of the prefecture, have severely dropped. The annual damage of more than 200 million yen exceeds that of agricultural products caused by animals such as bears and wild boars, which accounts for around 150 million yen annually.

( Translated by The Japan News )


 【 2020年8月11日付・福島民友新聞掲載 】