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.

The Skellam model describes discrete-time population dynamics of a single species assuming uniform (i.e., random or Poissonian) individual distribution and intraspecific contest competition. Apart from studies on individual-based models derived from first principles, it has rarely been applied to ecological research. However, in specific situations, it may be more appropriate than, for instance, the frequently used Ricker model. This is derived from assuming scramble competition among individuals. In this paper, we offer insight into the first principles underlying the Skellam model. In addition, we provide an alternative parameterization of the model in terms of two commonly used parameters: intrinsic rate of population increase and carrying capacity. In light of these findings, the Skellam model may be a useful alternative for a range of purposes where it has previously been overlooked, e.g., in fitting population models to time series data.

Body size of individuals is typically increasing towards colder and higher latitudes, as larger body size is known to be a thermoregulatory adaptation to colder circumstances. Here we explored the spatio--temporal changes in wing length and body weight of 24 wintering bird species in Northern Europe and how these relate to annual changes in winter temperature. We show that across all species, body size has decreased since the 1970s, with a negative relationship between wing length and temperature anomalies of previous winters, suggesting carry over effects likely linked with body size--related survival or dispersal. Body weight was negatively related with the temperature anomaly of the same winter, indicating more immediate effects related to reduced fat reserves during mild winters. Our results highlight climate--driven decrease in body size across several species and its' association with annual variation in winter temperature in the high latitudes.