Factors affecting mandarin ducks (Aix galericulata) wintering at dam lakes in the Chugoku district, western Japan.

Wintering mandarin duck (Aix galericulata) populations and their behavioural adaptations were analyzed in relation to habitat conditions at six dam lakes in the Chugoku district of western Japan, from September 1999 to March 2000. Mandarin duck densities in the dam lakes were significantly correlated with the shoreline bordered by trees. Mandarin duck densities in the dam lakes were also affected by the decrease in the water level. Overhanging branches and dense vegetation along the shoreline provided mandarin ducks with suitable resting cover and shelter. Receding water levels made resting cover unavailable by exposing these sites. The most notable response to a decline in water level was to move into sites with abundant cover such as those found in pools of the inflow rivers. Since it is practically impossible to maintain constant water levels in dam lakes, we suggest that small adjacent impoundments with sufficient cover should be built to attract mandarin ducks to artificial reservoirs.