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