Evaluation of a potential umbrella species using favourability models: the case of the endangered little bustard (Tetrax tetrax) and steppe birds

Abstract

Farmland biodiversity is in alarming decline worldwide due to agriculture intensification. In this context, the umbrella species concept may help in better targeting conservation efforts, focusing on species whose requirements may best cover those of other components of biological communities. We test this idea using the little bustard (Tetrax tetrax), a strongly declining steppe bird depending on extensive agricultural landscapes of south-western Europe, to explore the degree to which its habitat requirements can predict those of other sympatric endangered steppe birds. We use little bustard and other nine species distribution data at 10 × 10 km scale in Castilla-La Mancha (the most important region for the little bustard in Spain and the EU) and habitat favourability models to identify variables explaining little bustard favourability that can robustly predict habitat favourability also for the other nine species. Models fitted with variables explaining little bustard favourability and applied on co-occurring species yielded varying performance results. Models support the role of the little bustard as umbrella species only for a part of the steppe bird community, and more precisely, for species linked to cereal and grassland-dominated landscapes, but not for landscape generalist species, distributed over mosaic landscapes including shrublands and woody crops. Results also highlight the importance of favourable extensive cereal steppes for the conservation of strongly endangered species (little and great bustard, Montagu’s harrier, pin-tailed sandgrouse, calandra lark), some of which are largely understudied (pin-tailed sandgrouse and calandra lark), despite their marginal coverage by the Natura 2000 protected area network.