Arizaga J., Castilló J. & Josa P. (2025) Mountain grasslands as a stopover habitat for Red-backed Shrikes Lanius collurio in the Pyrenees. ARDEA 113 (2): 185-194

Understanding how birds use stopover areas is essential for the effective conservation of migratory bird populations. Here, we evaluate the role of high-altitude grasslands in the Central-Eastern Pyrenees as autumn stopover habitat for the Iberian population of the Red-backed Shrike Lanius collurio. Using data from a standardized mist-netting program (2010–2024), we analysed age-related patterns in abundance, fuel load, fuel deposition rate and stopover duration. First-year birds were captured much more often (91.5%) and they did not have a longer stopover duration than adults. However, both age classes had a low mean fuel load (0.0338 ± 0.0536 SD, i.e. 3.4%) and a minimal fuel deposition rate, suggesting that the Pyrenees might not serve as a main refuelling site. Instead, the region may function as a transient area for the shrikes, particularly for first-year birds at the onset of their first migration. Despite the low fat accumulation, the high number of individuals using this area highlights its potential relevance. The mosaic of pastures and open habitats aligns with the shrikes’ foraging preferences and may support a migration strategy based on short-distance flights with low energy reserves. Given the ongoing population decline and habitat loss, preserving these herbaceous areas is critical to ensure safe passage for species like the Red-backed Shrike. Our findings underscore the need to protect not only key fuelling sites but also early-phase resting habitats along migratory flyways.