Modelling the effectivity of a land sparing strategy to preserve an endangered steppe-land bird population in cereal farmland: scopes and limits

Abstract

Agricultural intensification and the disappearance of fallow land have been identified as a major driver of biodiversity loss in European farmland. In particular, the dramatic population decline of the little bustard (Tetrax tetrax), a flagship bird species in western European cereal farmland, has been largely attributed to the loss of this crucial habitat. Demographic modelling showed that low breeding success and reduced female survival were co-responsible for the little bustard population decline in a NE Iberian cereal pseudo-steppe. An equilibrium finite rate of change can be achieved by raising either female adult survival or fecundity. In both cases, the required increases fall within a biological meaningful range, but a combination of both would be more feasible in practice. Setting farmland aside as managed fallow can boost fecundity to the required equilibrium value, but the potential of this management action is seriously reduced as mortality increases. Socio-economically acceptable amounts of spared-land can only be achieved if actions to reduce mortality are undertaken in combination with providing fallow land. Actions to reduce both natural and anthropogenic mortality have so far been neglected by little bustard conservation programs. Both are needed if we seek to guarantee the long-term viability of the species and an acceptable share of conservation effort from stakeholders. Our results show that the holistic adaptive management approach adopted here can be used to evaluate the effectiveness and limitations of conservation decisions and to provide insights for conservation projects.