Habitat- and density-dependent demography of a colonial raptor in Mediterranean agro-ecosystems

Abstract

Agricultural intensification is considered the major cause of decline in farmland bird populations, especially in the Mediterranean region. Food shortage increased by the interaction between agricultural intensification and density-dependent mechanisms could influence the population dynamics of colonial birds. Weused demographic data on lesser kestrels (Falco naumanni), a key species of Mediterranean pseudo-steppes, to understand the importance of land-use changes and density-dependent mechanisms in the light of its fluctuating conservation status in the Western Palearctic. Our analysis indicated an important influence of land uses (artichokes, arable and grassland fields) and colony size on kestrel survival rates. The strong habitat effect revealed the unsuitability of intensive arable lands with respect to extensive grasslands for lesser kestrels. Notably, artichokes, a winterintensive crop, proved to be a high-quality habitat as they were associated with survival values equal to those of grassland. This is likely due to prey availability and reveals that non-traditional crops may provide suitable habitats for lesser kestrels. Information theory gave strong support to the negative influence of colony size on fecundity, albeit a small one, for its positive effect on survival probability. The estimated population growth rate was negative for all three habitats, indicating a decline over time and urging conservation actions in all of the areas studied. This decline was much higher in colonies surrounded by arable fields. In sensitivity analyses, λ indicated that adult survival was the parameter with the greatest effect on population growth, followed by survival of fledglings and fecundity. Our study showed howthe costs and benefits of group living interact with agricultural intensification to drive species demography. In addition, we integrated significant information on one of the largest lesser kestrel populations to fine tune the most effective conservation strategy to prevent the collapse of the species in a relevant part of its range.