Long-term spring arrival dates of 37 migratory bird species as recorded in Moravia (Czech Republic) during 103 years between 1881 and 2001 were evaluated for pairwise correlation (i.e. co-fluctuation in migratory timing) between avian species. Cluster analysis of the correlation matrix revealed a number of clusters (called ‘migrons’) of co-fluctuating migratory bird species. All short-distance migrants with the European (Mediterranean) winter range clustered together in migron A (Alauda arvensis, Motacilla alba, Vanellus vanellus, Sturnus vulgaris, Corvus frugilegus, Columba palumbus, Phoenicurus ochruros, Phylloscopus collybita, Remiz pendulinus, Erithacus rubecula, Turdus philomelos, Larus ridibundus, Serinus serinus, Sylvia atricapilla), while six other, smaller clusters were formed exclusively of long-distance migrants having an African (sub-Saharan) winter range: (B) Cuculus canorus, Streptopelia turtur; (C) Hirundo rustica, Jynx torquilla, Luscinia megarhynchos, Apus apus, Sylvia curruca; (D) Acrocephalus schoenobaenus, Riparia riparia, Upupa epops; (E) Anthus trivialis, Delichon urbica, Motacilla flava, Hippolais icterina; (F) Ciconia ciconia, Phoenicurus phoenicurus, Ficedula albicollis, Acrocephalus arundinaceus, Lanius collurio; (G) Oriolus oriolus, Muscicapa striata, Locustella fluviatilis, Coturnix coturnix. Results of the co-migration analysis pose interesting questions about possible varying underlying mechanisms of the migration timing in different migrons of birds.
The North Atlantic Oscillation (NAO) has been used as a simple approximate descriptor of the global weather fluctuation over Europe. Spring arrival dates of 37 migratory bird species (summer visitors) recorded in Moravia, Czech Republic during 103 years between 1881 and 2001 were correlated with the seasonal NAO index. Bird arrivals occurred significantly earlier following positive winter/spring NAO values (causing a warmer spring than normal in Central Europe) in all short-distance migrants with a European (Mediterranean) winter range (Alauda arvensis, Anser anser, Columba palumbus, Larus ridibundus, Phoenicurus ochruros, Phylloscopus collybita, Remiz pendulinus, Saxicola torquata, Serinus serinus, Sturnus vulgaris, Turdus philomelos, Vanellus vanellus). On the other hand, the timing of arrival did not correlate significantly with seasonal NAO in long-distance migrants having largely an African (sub-Saharan) winter range (Acrocephalus schoenobaenus, Anthus trivialis, Apus apus, Ciconia ciconia, Cuculus canorus, Ficedula albicollis, Hippolais icterina, Hirundo rustica, Jynx torquilla, Lanius collurio, Luscinia megarhynchos, Muscicapa striata, Oriolus oriolus, Phylloscopus sibilatrix, Riparia riparia, Streptopelia turtur, Sylvia atricapilla, S. curruca, Upupa epops). The prevailing positive phase of winter/spring NAO conditions observed in Europe at the end of the 20th century has obviously determined the trend of an earlier than normal arrival of short-distance migratory species.