Order Chiroptera is characterized by great variability in foraging, roost and social strategies. Greater mouse-eared bat (Myotis myotis, Borkhausen 1797) is a model species of a bat in Europe and his seasonal organisation of population represents typical temperate bat cycle with females aggregated in large maternity colonies and solitery roosting males. Although the M.myotis is a model species, the majority of studies were focused on different aspects of maternity colonies biology and the biology of males is still poorly known. Recently founded aggregations of males of M. myotis in highway bridges allow to study social behaviour and acoustic communication of males on between individual level and discuss these findings with known information. While the bridge in Bernartice was inhabited by aggregation of males in individual roosts, in Voznice bridge we found besides males also a maternity colony of M. myotis. Harems of males were established from august until october. We found different pattern of seasonal roost occupancy in males with males with the highest level of mean occupancy having the highest level of female presence in roost. Vocalisation activity of males increased in august with highest level of activity in september. Males roosting closer to the flight entrance tended to have higher...