Institute of Livestock and Grassland Science, NARO

Ducks and coots can eat lotus root in the mud of lotus field

- To understand the "duck damage" against lotus root at night -

National Agriculture and Food Research Organization (NARO) has confirmed feeding damage by wild ducks and coots to the lotus roots in the mud of water-filled lotus fields. We experimentally placed lotus roots in a lotus field and recorded the waterfowl's behavior at night. As a result, Mallards and Eurasian Coots upended and ate the lotus roots to a depth of about 40 cm below the water surface. Mallards also dug mud with their legs. The results of this study can be used effectively against the lotus root damage (approximately 300 million yen per year) around Lake Kasumigaura, which accounts for about 10% of the agricultural crop damage caused by birds in Japan. This knowledge is indispensable for effective damage control measures based on scientific evidence.


Feeding damage to the lotus root caused by ducks and coots has been reported around Lake Kasumigaura in Ibaraki Prefecture, Japan's top production area of lotus roots. The damage is about 300 million yen annually (FY2020), which accounts for about 10% of the agricultural damage caused by birds in Japan.

It is extremely difficult to directly observe the damage because the lotus roots are grown in the mud of the flooded lotus fields, and feeding damage occurs at night. Lotus roots with damaged scars, which lost commercial value, have been widely recognized as "duck damage" because the flocks of ducks can be seen in lotus fields at night during the harvest season from autumn to winter. But there was no previous conclusive evidence confirming that waterfowl forage the roots. Anti-bird nets have been installed in many lotus fields as a countermeasure, but it is difficult to prevent bird intrusion completely, and the net causes many deaths of entangled wild birds and becomes a conservation problem. Clarifying the species causing damage and their feeding behavior is essential to understand the actual damage and implementing effective countermeasures.

NARO experimentally set lotus roots in post-harvest lotus fields and recorded the feeding behavior of waterfowl at night. We observed Mallards and Eurasian Coots ate the lotus roots in the mud (approximately 20-40cm below the water surface) while upending repeatedly. Mallards also dug mud with their legs. By the next morning, a bowl-shaped hollow had been made in the mud surrounding the lotus root, and the uneaten lotus root remained 40cm or deeper beneath the surface. Although further investigation is required due to the small sample size, some duck species were observed not to cause feeding damage.

These results showed that Mallards and Eurasian Coots, at least, cause damage to pre-harvest lotus roots with commercial value, especially in shallow water. Also, lotus fields could become suitable habitats for many waterfowl wintering in the Lake Kasumigaura region. The consequence helps to grasp the actual "duck damage" that occurs at night and will be an essential finding for considering future countermeasures.

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