Changes with Time in the Songs of a Population of Chaffinches

A comparison has been made between 23 song types recorded from Chaffinches in Stanmer Great Wood, Sussex, U.K. in 1960, and the total of 36 that were sung there in 1978. Eight of the earlier song types showed clear similarities with those present in 1978: in three of these the differences were minor, but in the other five they were substantial enough for the songs to have been classified as different types had they been found in the same population at the same time. With all other song types, the differences were too great for song types to be compared between the two sets of recordings. While at any one time some song types are shared in more or less identical form among many individuals in a population of Chaffinches, these results show that the form of song types changes through time. These changes may occur because rare song types are not copied by other birds and become extinct in the area, because new song types are introduced from elsewhere by birds moving into the area and because mistakes in copying may lead to new song types being generated.