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Grassland birds are among the most threatened and fastest declining terrestrial vertebrate species in Europe, principally due to agricultural intensification and transformation. The little bustard is a priority grassland bird under the European Directive (2009/147/CE) that led to the classification of a network of Special Protected Areas (SPAs) in Portugal. A third national survey carried out in 2022 reveals a worsening of an ongoing population collapse at a national scale. The population declined by 77% and 56% compared to the previous surveys in 2006 and 2016, respectively. We found that the little bustard has greatly disappeared outside SPAs, while the remaining breeding population concentrated within the protected area network is showing a steep decline at a rate of 9% a year. This decline is now twice as fast when compared to the period 2006–2016. Analysis of the variation of the breeding densities between 2006 and 2022 at 49 survey sites revealed that those that initially had higher bustard densities and shifted toward a higher proportion of cattle among the total stocking rate experienced steeper declines. Areas where the density of roads increased also experienced declines over the course of the study period. Agricultural areas converted to or dominated by beef production likely relate to low breeding success and mortality of nesting females in fodder crops. Still, major habitat conversion outside SPAs to permanent crops led to overall habitat destruction, which contributed to the species decline and range contraction. Other threats are likely acting synergistically such as fragmentation, climate change and anthropogenic mortality. The extinction of the little bustard in Portugal is expected in the short term if no conservation actions are put in place. [ABSTRACT FROM AUTHOR]

Collision with power lines is a major cause of mortality for many bird species. Understanding the biotic and abiotic factors that increase collision risk is therefore important for implementing mitigation measures to minimize mortality, such as power line rerouting or wire marking. Here, we used collision events registered during 2003–2015 along 280 km of transmission power lines in southern Portugal to analyse spatio-temporal patterns and collision risk factors in two sympatric, threatened, and collision-prone species: the great bustard Otis tarda and the little bustard Tetrax tetrax. The occurrence of collisions was not uniform across space and time, and variations could be explained by the species' ecological requirements, distribution patterns and behaviour. Although both species fly considerable distances between areas of suitable habitat, collisions were far more likely in power line sections with > 20% (for the little bustard) or > 50% (for the great bustard) of open farmland habitat in the surroundings. Power line configuration was also important: taller pylons and those with a higher number of wire levels posed a higher risk for both species. Wire marking had a small but significant effect for the little bustard, reducing collisions risk. There was, however, no similar effect for the great bustard, possibly a result of limited data. Mitigation measures should be implemented to prevent bustard collisions, including adequate route planning, ideally avoiding areas with > 20% of open habitat. Line configuration and wire marking are particularly important where such localities cannot be avoided and power lines cross areas with a high proportion of bustard habitat, including outside protected areas. [ABSTRACT FROM AUTHOR]

Migratory decisions, such as the selection of stopover sites, are critical for the success of post‐breeding migratory movements and subsequent survival. Recent advances in bio‐logging have revealed the stopover strategies of many long‐distance migrants, but far less attention has been given to short‐distance migrants. We investigated the stopover ecology of an endangered grassland bird, the Little Bustard Tetrax tetrax, a short‐distance migrant in Iberia. Using high‐resolution spatial GPS/GSM data, 27 male Little Bustards breeding in southern Portugal were tracked between 2009 and 2011. We studied post‐breeding movements using Dynamic Brownian Bridge models to identify the main stopover sites, and generalized linear mixed models to examine habitat selection in stopovers. During their post‐breeding movements, males were essentially nocturnal migrants, making frequent stopovers while maintaining a relatively fast pace to reach more productive agricultural post‐breeding areas. Stopovers occurred in most post‐breeding movements (83%) regardless of the total distance covered (average 64.3 km), and most stopovers (84%) lasted less than 24 h. Birds used mostly agricultural non‐irrigated and irrigated croplands as stopover sites and avoided other land uses and rugged terrain. There was a negative relationship between stopovers and the proximity to roads, but not to power lines. The high frequency of stopovers during post‐breeding movements, despite the short distances travelled, together with the nocturnal migratory behaviour of bustards, may impose additional risks to a bird mainly threatened by collision with power lines in non‐breeding areas. We also conclude that even for short‐distance migrants, habitat connectivity between breeding and post‐breeding areas is likely to be a key conservation concern. [ABSTRACT FROM AUTHOR]

Environmental impact assessment (EIA) follow-up monitoring in energy projects, such as wind farms, solar facilities and power lines, frequently encompasses bird fatality surveys based on regular carcass searches. Since a large number of bird carcasses are often not found, field experiments to determine carcasses persistence (CP) and searcher efficiency (SE) biases in fatality surveys are typically performed for every single project. These data are, however, rarely used beyond the scope of each original project. We compiled data from CP and SE trials performed under 36 independent monitoring programs aiming to assess bird mortality at transmission lines in Portugal, whose results were until now unavailable or dispersed in grey literature. We used survival analysis and generalized linear mixed-effects models to investigate the ecological and methodological factors influencing CP times and SE rates. Bird carcass size was a key driving factor of both CP times and SE rates of human observers, which were consistently out-performed by scent detection dogs. Season and habitat interactions had also an important role in CP patterns, while variations in SE rates by human observers were largely influenced by ground visibility (i.e., a combination of ground cover and vegetation height). Our results reinforce previous studies indicating that CP and SE biases are site-specific and determined by a wide range of ecological and methodological factors not always accounted in standard trial designs. Overall, our study demonstrates that data routinely collected under bird monitoring programs from multiple projects can be combined to identify broad ecological patterns, limitations of current studies and, ultimately, improve EIA follow-up practice. • Data from EIA follow-up monitoring is rarely used beyond each original project. • We compiled bias-correction data of bird fatality surveys in multiple transmission lines. • Bias-corrections were affected both by ecological and methodological factors. • Despite the broad patterns, bias-correction values were often site-specific. • Monitoring data from multiple projects can be combined to inform EIA practice. [ABSTRACT FROM AUTHOR]

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 densities. [ABSTRACT FROM AUTHOR]