Abstract
Observations in central Wakayama Prefecture revealed the effect of number of individuals and water level on the diversity of foraging behaviour of Teal Anas crecca. Wintering numbers peaked during October and November and again during March and April. The most frequent foraging behaviour was dabbling or dipping in 4-17 cm deep water. However, foraging on shore or in water deeper than 24 cm was observed during the periods of peak numbers. Comparing the diversity index H’ of foraging behaviour and number of individuals, H’ during the low density period was significantly lower than that during the high density period. This shows that Teal begin to forage in less usual places and using unusual methods, following an increase in the number of individuals. In contrast, the effect of water level on H’ was significantly weaker than the number of individuals. This effect was considered to be the result of temporary increases in water level, following precipitation. In conclusion, the study revealed that Teal begin to forage on shore or in water deeper than 24 cm when the number of individuals increased, though foraging by dabbling and dipping in 4-17 cm of water was common, leading to high diversity in foraging behaviour.
