Effekter av predationsrisk på sånglärkors (Alauda arvensis) habitatval på åkermark

Abstract: Along with other European farmland birds, the skylark (Alauda arvensis) has declined rapidly since the 1970’s. Between 1975 and 2003, the Swedish population of skylarks declined with 64 %. In Britain, the decline is often explained by alterations in farming practices in general and the shift from spring-sown to winter-sown cereals in particular. The dense vegetation structure of winter cereals is limiting the number of breeding attempts possible, causing the entire population to decline. In Sweden, however, the proportion of winter-sown cereals has remained stable and cannot be held responsible for the decline. Furthermore, Swedish skylarks do not perform as many breeding attempts as their British relatives and the popu-lation is therefore not as dependant on opportunities to rebreed. On the contrary, the dense structure of winter cereals could benefit Swedish skylarks since it offers slightly more pro-tection from predators. Given the high proportion of presumably predator-friendly forest edges bordering arable fields in Sweden, it is likely that any possibility to nest closer to forest edges would be beneficial for the skylark, since it would make larger areas avail¬able as habitat.In this study it is examined how the habitat preferences of Swedish skylarks are af-fected by winter- and spring-sown cereals in fields where adjacent forest edges causes pre-dation risks to increase. Information on the distribution of singing skylarks in fields sown with winter wheat, spring-barley and oats has been analyzed using a General Linear Mixed Model (GLMM) in order to investigate how territory densities are affected by the three way-interactions between the date of the inventory, the sowing-time and the presence of forest edge adjacent to the field.Results show that territory densities in winter-sown cereals decline significantly during the season. In spring-sown cereals, densities increase significantly in fields adjacent to forests and remain stable on fields with no forest edge. Thus, skylarks seem to prefer fields with low predation risks and/or adequate protection during the early part of the season. As winter-sown fields become too dense, skylarks move away, possibly to previously unin-habited spring-sown fields bordering forest edges. Consequently, both winter- and spring-sown cereals can be beneficial to Swedish skylarks, especially if they occur close enough to allow birds to move between them during the season. From a nature conservation point of view, sowing winter- and spring cereals next to each other would be advisable, primarily when fields border on forest edges as is common in Sweden.