Scarlet rosefinches have shown a distinct expansion pressure towards Middle and Western Europe throughout the last decades. The reason for this phenomenon appears to be complex. Bioacoustics in general and the occurrence of dialects in particular might give some hints for recognition of certain aspects of it. The investigations were carried out in Middle European areas such as Hiddensee Island, Lower River Oder and Warthe and southern Bohemian Forest in 1994 and 1995. Male scarlet rosefinches have a well-structured song repertoire that is used depending on situation and level of learning process. Each male develops two song types, defined as short and long song type. Particularly the short song type shows a certain population specificity. Juvenile males in general have a more distinct deviation from the population dialect than have adults. That points to a possible link between dialect development and expansion tendencies.