Environmental and geographical constraints on common swift and barn swallow spring arrival patterns throughout the Iberian Peninsula

摘要: Aim  Still poorly understood, the main migratory pathways for most trans-Saharan species pass through Iberian Peninsula, which acts as a gateway to European–African system. Arrival patterns in this region common swift (Apus apus) and barn swallow (Hirundo rustica), of similar morphology flight capabilities, were described, environmental geographical factors best explaining them examined, search ecological constraints on these two species. Location  Latitude ranged from 36.02 43.68°N, longitude 9.05°W 3.17°E, altitude 0 1595 m a.s.l. 482 812 Spanish localities spread widely over breeding grounds species. Methods  Our data set, covering years 1960–1990, consisted 3206 first-arrival dates swifts 6036 swallows. Forty topographical, climatic, river basin, spatial variables used explanatory general regression models (GRMs). GRMs included polynomial terms up cubic functions all when they significant. A backward stepwise selection procedure was applied until only significant remained. steps. First, we searched model each one five types (topographical, spatial). To cope with unavoidable correlation between variables, relative importance type variable assessed by hierarchical variance partitioning. Secondly, that able explain maximum amount observed variability arrival date. obtain subjected jointly GRM. Spatial then added take any remaining structure into account. Moran's I autocorrelation coefficient check autocorrelation. Results  Both arrived earlier south-western where summers are warmer drier. From there, both followed southern basins towards north-east; however, several mountainous regions impede colonization eastern Iberia. The explained 19–47% 14–44% dates. Variance partitioning indicated climatic variability. predictive built accounted 52% 50% swallow. Residuals not spatially autocorrelated, an indication major structured variation had been for. Main conclusions  Spring highly dependent configuration Peninsula. This constraint forces converge very closely their spring migration, because swallows subject trade-off optimum territories ecologically suitable breeding.