Evidence of climate change effects on within-winter movements of European Mallards Anas platyrhynchos

Other than during periods of migration, animal movement tends to be poorly described, despite the potential importance of such movements, which may prove crucial for surviving periods of bad weather and low food availability. We analysed within-winter (December-February) movements of Mallard using the EURING Data Bank. Most movements were directed towards the south or southwest during all three winter months. Distances covered increased with winter harshness and generally decreased from 1952 to 2004. Mallards appear to move less than other duck species during winter. Long-distance movements of Mallards seem to be related to cold weather, birds only moving long distances in large numbers during the very coldest winters. Movements are not restricted during midwinter, but occur throughout the winter. The decreasing within-winter movement over time (1952-2004) could be explained by decreasing reporting probabilities and/or warmer winters in recent decades. However, the first is only true if the decrease in reporting probability increases with distance moved, for which we found no indication in our study. Therefore, we suggest that the pattern found is evidence of long-term winter warming reducing the distance of within-winter movements in this species.