Responses of Great Bustard (Otis tarda) subpopulations to land-use changes in southwestern Iberia

Land-use change is the single most important cause of global biodiversity loss. Over millennia, European grassland birds concentrated in low-intensity agro-steppe habitats that are now experiencing intensification largely in line with European market forces. Great Bustard (Otis tarda, GB) is a globally threatened species and a symbol of the Iberian agro-steppes. In Extremadura (Spain) and Alentejo (Portugal) the conservation status of GB and other agro-steppe species is unclear. GB subpopulations were monitored in these two regions between 1985 and 2015, and their trends were related to land-use changes using open-access databases. There was regional variation in trends, and I report here a sharp decline in numbers across the study area since 2010. Trends were not related to moderate reduction of agro-steppe habitats, but were negatively related to changes in livestock densities, implying that livestock management of habitats is crucial for conservation. Using field counts in spring 2017 across a network of EU Special Protected Areas (SPAs) designated to protect GB, I found that GB is not a good indicator for other agro-steppe species of conservation concern. Selection of further indicator species is recommended for better conservation of agro-steppe bird assemblage. In an SPA in Extremadura, GB productivity rates decreased dramatically between 2005 and 2016. If current productivity rates continue, population modelling predicts a steep decline in numbers at this site. Results of this study raise concerns over the function of the SPA network in Extremadura and Alentejo to protect GB and their agro-steppe habitat. To sustain numbers of GB and other agro-steppe species, their habitats need to be better protected from further intensification, including control of livestock densities, preferably using agro-environmental schemes in PAs.