Factors affecting the diet of farmland skylarks Alauda arvensis.

Abstract

1. The diets of skylarks on three farmland areas, determined by faecal analysis, are described and compared. Similarities between the feeding ecology of some of the common farmland bird species are pointed out.
2. The feeding rates and the sizes and metabolizable energy contents of food items are established for skylarks using each of the three main winter foraging methods. This permits the calculation of rates of metabolizable energy intake from foraging.
3. Birds fed on cereal grain from stubbles and sowings when it was available. These food sources gave rates of energy intake higher than were found for the other foraging methods. However these other food sources were used to some extent even when grain was widely available.
4. When cereal grain was unavailable, in late winter, skylarks could either search ploughed land for weed seeds or graze the leaves of winter wheat. The rate of energy intake possible from feeding on seeds varied with seed size and density but that from grazing was relatively constant from field to field. Birds spent more time foraging for seeds on ploughed land than grazing only where seed densities and sizes allowed a higher rate of energy intake from searching for seeds than from grazing. Where seed densities were low, leaves formed the greater part of the food in late winter.