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.