White-fronted geese (Anser albifrons) forage on young leaves of wheat as well as rice grains in agricultural fields around Lake Miyajimanuma in Hokkaido, which is a migratory stopover site, causing wheat damage every spring. Behavioral characteristics of foraging patch selection of the geese have been studied, and fat reserve before leaving the stopover site has been clarified. The aim of this study was to elucidate the characteristics of field choice of the geese in relation to their fat level in order to solve wheat damage problems. Spatial and temporal patterns of field choice of the geese during the spring and fall staging periods in 2011-2012 were surveyed. Fat deposition level was estimated as the abdominal profile index, and pace rate was measured as the number of steps in 60 seconds for a randomly selected foraging goose in each field of rice stubble and wheat leaves. The distribution of geese was mainly in rice-stubble fields in early spring but changed to wheat fields in late spring. Fat deposition levels of the geese in wheat fields were significantly higher than those of geese in rice fields. No significant difference was found in numbers or pace rates of geese in wheat fields at different distances from the lake. The geese used rice fields near the lake in early spring but used rice fields far from the lake in late spring. The pace rate of geese in rice fields in late spring was significantly higher than that in early spring, and it was also higher in rice fields nearer to the lake. The results indicated that the density of rice grains was decreased in fields nearer the lake, the roost patch, especially in late spring. Geese with a high fat deposition level might forage in wheat patches due to the abundance of food density despite the low energy level of wheat leaves. On the other hand, geese with a low fat deposition level might forage in rice patches distant from the roost patch with a high predation risk because they give priority to fat accumulation. These results support the proposition that the wheat damage problem can be resolved by setting up an alternative feeding area of green manure crops to attract geese with high fat deposition levels.
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State-dependent foraging of the Greater White-fronted Geese Anser albifrons
マガン Anser albifrons の状態依存採餌における採食地利用
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