Habitat characteristics and the rate of decline in a threatened farmland bird, the Ortolan Bunting

Farmland habitats are witnessing steep declines in biodiversity. One rapidly declining farmland species is the Ortolan Bunting. In Finland, a staggering 99% of the population has been lost during the past 30 years. Changes in the breeding habitats have been proposed as a reason for the decline, although hazards during migration and wintering may also play a role. We gathered a 19-year data set of Finnish Ortolan Buntings and studied which spatial characteristics, habitat features, and climate factors might explain the population growth rate at the singing-group level. As explanatory variables we used region, density of small-scale landscape structures, proportion of agricultural area in the landscape, diversity of crop types, proportion of bare ground, and temperature and precipitation of previous breeding season. The only region with a marginally positive growth rate was North Ostrobothnia, where the species often occupies newly established fields. High crop type diversity mitigated the declines by perhaps providing a wide array of feeding, hiding and nesting places. Bare ground benefited Ortolan Buntings by perhaps providing an easy access to food. The last Ortolan Buntings occurred in landscapes dominated by interconnected agricultural land which, we think, reflects the species’ sociability and avoidance of forested areas. We suggest that agricultural intensification and the following potential reduction in food availability may be a cause of the decline of Ortolan Bunting. As general conservation measures, such as promoting set-aside land or field margins, have been inadequate, either in effect or in extent of application, it is evident that work remains. Northern populations of Ortolan Bunting should be targeted for further studies on feeding and breeding ecology as well as for urgent conservation actions, such as increasing crop type diversity and bare ground. Promoting more multi-functional and agro-ecologically managed agricultural landscapes would benefit a wider range of farmland species as well.