The effect of atmospheric circulation on spring arrival of short- and long-distance migratory bird species in Estonia

The aim of this study was to analyse and identify preferred atmospheric circulation conditions for migratory birds during their spring arrival in Estonia (for Tartu and Kuressaare). A total of 47 circulation classifications and 42 common bird species were studied. The analysis identified a clear division of species into two general clusters according to their preferred circulation conditions. Short-distance migrants preferred predominantly cyclonic conditions with winds from the south-west, while for long-distance migrants windless anticyclonic conditions were preferred. The former were also less dependent on circulation than the latter. Short-distance migrants reaching Tartu were more dependent on circulation than those reaching Kuressaare. The classifications created by the methods CAP, CKM and SAN indicated stronger associations with bird arrival than those based on the methods NNW, PXK and SOM. Clear species sub-clusters were identified for the Tartu migrants only, distinguishable in the strength of the dependence on circulation or the preferred circulation conditions.