European grassland birds are experiencing major population declines, mainly due to changes in
farmland management. We analyzed the role of habitat availability, grazing management and
linear infrastructures (roads and power lines) in explaining spatial and temporal variation in the
population density of little bustards (Tetrax tetrax) in Portugal, during a decade in which the species
population size halved. We used data from 51 areas (totaling ca. 1,50,000 ha) that were sampled
in two different periods (2003–2006 and 2016). In 2003–2006, when the species occurred at high
densities, habitat availability was the only factor affecting spatial variation in bustard density. In the
2016 survey, variation in density was explained by habitat availability and livestock management,
with reduced bird numbers in areas with higher proportions of cattle. Population declines across the
study period were steeper in areas that initially held higher densities of bustards and in areas with a
higher proportion of cattle in the total stocking rate. Areas with higher densities of power lines also
registered greater density declines, probably due to avoidance behavior and to increased mortality.
Overall, our results show little bustards are currently lacking high quality grassland habitat, whose
persistence depends on extensive grazing regimes and low linear infrastructure densitiesinfo:eu-repo/semantics/publishedVersio