Ecological conditions in wintering and passage areas as determinants of timing of spring migration in trans‐Saharan migratory birds

摘要: Summary1. Climate change has been associated with shifts in the timing of biological events, including thespring arrival migratory birds. Early at breeding sites is an important life-history trait,usually higher success and therefore, susceptible to selection evolu-tioninresponsetochangingclimaticconditions.2. Here, we examine effect changes environmental conditions wintering pas-sage areas on mean passage time 13 trans-Saharan passerines during their spring migrationthroughthewesternMediterraneanoverthe15 yearsfrom1993to2007.3. We found that most species studied have advancing inrecentyears.However,annualvariationinthemeandateofpassagewaspositivelycorrelatedwithvegetation growth (measured as normalized difference vegetation index [NDVI]) both theSahel (the region departure) northern Africa area). Thus, migration dateswere delayed years high primary productivity zones. All speciesseem respond similarly NDVI Sahel; however, late migrants were less affected by eco-logical than those migrating earlier, suggesting differences based onspeciesecology.4. Mean was not related North Atlantic Oscillation (NAO), El Nin˜o-Southern (ENSO), temperature or species-specific (theoverwinteringregion)whenanalysedincombinationwiththeothercovariates.5. Our findings show ecological winter quarters (specifically Sahel) anden route are relevant factors influencing trends dates migratorybirds southern fringe Europe. Possible long-term consequences for arriving springmigrantsarediscussed.Key-words: bird migration, climate change, ENSO, Mediterranean, NAO, NDVI, northernAfrica,SahelIntroduction