Reed warblers migrating through Portugal: climatic influence on stopover ecology over the last decade

•The minimum stopover duration of reed warblers at Portuguese reedbeds decreased over the last decade.•Extended winter NAO index and temperature were the most important variables for spring migration.•Precipitation and temperature were the most important variables for autumn migration.•The wind can affect flight speed at departure and during the entire migration.

The arrival and breeding dates of small migrant birds have advanced throughout Europe. This study evaluates the hypothesis of a faster migration along the migratory route, which should lead to a decrease in stopover duration in staging areas over the last decades. Several climatic predictors were analysed as proxies to understand the stopover ecology of reed warbler Acrocephalus scirpaceus migrating through Central Portugal. The minimum stopover duration of migratory reed warblers decreased significantly over the last decade during both the spring and autumn migrations. Warmer conditions en route should increase food availability, increasing the body condition of departing birds and the quality of departing sites en route to Portugal, such that migrants will reduce the stopover duration at Portuguese reedbeds.