The spring timing of arrival of migratory birds: dependence on climate variables and migration route

Abstract

We analyzed the relationships between the spring arrivals of 42 migratory bird species breeding in Estonia, and mean March and April air temperature, the start of three spring-time climatic seasons, and two seasonal North Atlantic Oscillation (NAO) indices during the period 1957–1996. Regarding the spring arrival of migratory birds, we found two gen-eral clusters and six sub-clusters of species. All 23 species in one general cluster were short-distance migrants and all 19 species in the second one were long-distance migrants. The first arrival dates of short-distance migrants were strongly related to the seasonal win-ter NAO index (XII–III), mean March air temperature, the start of late winter, and the start of early spring. Generally, the first arrival dates of long-distance migrants were weakly correlated with climatic variables, but the first arrival dates of eight of these species was strongly related to the start of the climatic spring and/or mean April air temperature. The first arrival dates of eight species showed a significant trend over the observation period. The trends in the spring timing of arrival of the Rook and Whooper Swan were signifi-cantly related to the trend in the seasonal winter NAO index, while the trends in the spring timing of Mallard and Common Gull were significantly related to the trend in seasonal winter NAO index, mean March air temperature and start of early spring.