![]() Regarding grassland birds, several studies report high mortality levels due to collision, mainly with power lines, and a displacement effect related with human structures, as power lines, roads and wind farms, has also been described 27, 28, 29, 30. Roads and power lines are known to cause high levels of mortality of bird species 23, and population effects have already been described in raptors 24, bustards 25 and owls 26, among other bird groups. habitat loss and fragmentation), behavioral effects (avoidance and displacement due to disturbance) and mortality of numerous animal taxa 21, 22. Infrastructures are major drivers of human-related effects in the Anthropocene, associated with habitat changes (e.g. In addition to grassland management changes, infrastructures are also known to affect grassland birds. Even though these changes maintain grasslands, they potentially reduce the quality of the habitat for biodiversity by reducing landscape heterogeneity 17, and promoting changes in sward structure and crop management, e.g. In fact, such systems are being rapidly replaced by systems specialized on cattle and consequently increasing the proportion of pastures in the landscape 10, 11. Despite the ecological importance of these HNV systems, so far EU policies have failed to maintain these landscapes. The traditional management of these systems created a heterogeneous landscape due to the extensive cultivation of dry cereal crops in rotation with pastures to support sheep raising, which produced a patchy system of cereal fields, stubbles, fallow lands, plowed lands and pastures that supported a widely rich and variable grassland bird community, including several species with unfavorable conservation status at the European and world level such as great bustard ( Otis tarda), Montagu’s harrier ( Circus pygargus) or little bustard ( Tetrax tetrax) 14, 16. ![]() Grasslands or pseudosteppes of the Iberian Peninsula are considered key farmlands habitats for European biodiversity, mainly due to their importance for threatened grassland bird species 12, 13, 14, 15. For example, in Europe, changes in livestock management are promoted by the Common Agricultural Policy (CAP) through coupled payments (per livestock head), leading to an increase in livestock numbers, mainly cattle 10, 11. Often, these changes are supported by targeted policies. Intensification of management is usually associated to an increase in the use of agrochemicals or in livestock density 8, 9. However, they are often subjected to changes in management, such as conversion to other land uses, agriculture intensification or abandonment 3. Extensively managed High Nature Value (HNV) farmlands are recognized as key habitats for several taxa in Europe, namely butterflies 4 and birds 5, 6, and the maintenance of such landscapes is considered a priority for European biodiversity 7. Natural and semi-natural grasslands across the world are known for their high biodiversity value 1, 2, 3. Overall, our results show little bustards are currently lacking high quality grassland habitat, whose persistence depends on extensive grazing regimes and low linear infrastructure densities. Areas with higher densities of power lines also registered greater density declines, probably due to avoidance behavior and to increased mortality. 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. ![]() 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. In 2003–2006, when the species occurred at high densities, habitat availability was the only factor affecting spatial variation in bustard density. ![]() 1,50,000 ha) that were sampled in two different periods (2003–20). 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. European grassland birds are experiencing major population declines, mainly due to changes in farmland management.
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