Weather and body condition in wintering Mallards Anas platyrhynchos

Capsule Body condition in midwinter appears to be independent of climatic conditions. Aims To assess the long-term impact of climatic conditions on body stores, during the winter. Method Body reserves of male and female Mallards were determined in January over nine years on the same area of the Rhine River in Alsace, then related to ambient temperatures, water conditions, dietary indexes and potential for fasting endurance. Results Body mass, potential for fasting endurance, body lipids and proteins did not change significantly over the nine years (P > 0.05). Body reserves were not related to the extent of flooded areas (P > 0.10) or to ambient temperatures (P > 0.67) prevailing ten or 20 days before bird collection. In 1997 the occurrence of the severest cold spell for 30 years did not lower the Mallards' body condition or survival potential. This is probably explained by the observation that food was still available on unfrozen parts of the river and by a dietary shift by females towards molluscs. Conclusions Our results strongly support the hypothesis that the level of body nutrients in midwinter is endogenously regulated, and show that changes in climatic conditions prevailing in the Alsace during winter in the 1990s were not severe enough to significantly affect this level. The fact that the cold spell had no effect on the birds' body condition underlines the high value of this wintering area for Mallards.