Abstract
Assessing the diet of farmland birds during the wintering period has important implications for conservation. However, for some species such as the skylark, the diet composition remains poorly known across its wintering range. On the basis of gizzards collected in mid-winter over a 10-year interval and in two regions of Western France, we quantified the contribution of seeds and investigated whether the diet differed between sexes, regions and period and whether seeds entered the diet with respect to their size, nutritive value or their spring occurrence within the farmland landscape. Also, the amount of seeds that birds need to consume for meeting their daily energy requirements was assessed by simulation and compared with estimates measured in captive individuals. Thirty-eight seed species belonging to 16 families were identified in gizzards. All species but one were weeds, and cereal grains were absent from all gizzards. The diet differed slightly between sexes but contrasted between regions and periods. We found no clear evidence for a selective intake based on seed traits. Conversely, our results suggest that weed seeds would enter the diet with respect to their relative occurrence. Our simulation indicated that birds should ingest about 8 g (4200-5600 seeds) to meet their daily requirements. A mean value of 6.7 g per day was measured in captive skylarks. These results suggest that the maintenance of rich weed habitats is a crucial issue for populations of skylarks that overwinter in agricultural landscapes of Western France.