Abstract
In Great Tit song, a phrase of one to five notes is rapidly repeated in a strophe of a few seconds long. Great Tits sing up to 100 strophes of a single phrase version in a bout before a new phrase version is introduced. In 49 out of 69 phrase versions from 34 Great Tits analysed, phrases were repeated in a stereotyped fashion within strophes and within bouts. In the other 20 phrase versions, between 2 and 61% of the strophes showed song frequency plasticity (SFP). SFP is a phenomenon in which consecutive phrases within strophes are not 'identical' in structure because of abrupt differences in frequency characteristics across phrases. The percentage of strophes with SFP was significantly higher in phrase versions with (1) a higher note rate within strophes, (2) higher note frequencies (kHz), and (3) shorter notes. I suggest that motor constraints determine SFP and that these constraints play an important role in the manner in which Great Tit phrase versions are performed and composed.