From marking and recoveries, it has long been known that some bat species migrate between summer and winter haunts, e. g. Myotis dasycneme, Myotis lucifugus (e.g. Egsbaek and Jensen 1963; Davis and Hitchcock 1965). It has also been shown that some species undertake long distance seasonal north-south migrations, e. g. Miniopterus schreibersi, Nyctalus noctula, Pipistrellus nathusii, Vespertilio murinus in Europe and, e.g. Tadarida brasiliensis, Myotis sodalis in North America (Aellen 1983; Griffin 1970; Masing 1988, 1989; Petersons 1990; Strelkov 1969; Yalden and Morris 1975). It is also well known that bats are able to cross the sea since several species have been reported from many more or less remote Islands, oil rigs and ships (Baagoe and Bloch 1994; Petersen 1994; Stansfield 1966). Among these records, migratory species prevail.