In Great Tit song, a phrase of one to five notes is rapidly repeated i
n 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 in
troduced. In 49 out of 69 phrase versions from 34 Great Tits analysed,
phrases were repeated in a stereotyped fashion within strophes and wi
thin bouts. In the other 20 phrase versions, between 2 and 61% of the
strophes showed song frequency plasticity (SFP). SFP is a phenomenon i
n which consecutive ph rases within strophes are not 'identical' in st
ructure because of abrupt differences in frequency characteristics acr
oss phrases. The percentage of strophes with SFP was significantly hig
her 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 im
portant role in the manner in which Great Tit phrase versions are perf
ormed and composed.