The links between ecology, behavioural plasticity and brain size are o
ften tested via the comparative method. Given the problems in interpre
tating comparative tests of learning and cognition, however, alternati
ve measures of plasticity need to be developed. From the short notes s
ection of nine ornithological journals, two separate, exhaustive data
sets have been collated on opportunistic foraging innovations in birds
of North America (1973-1993; N=196) and the British Isles (1983-1993;
N=126). Both the absolute and relative frequencies (corrected for spe
cies number per order) of innovations differ between bird orders in a
similar fashion in the two geographical zones. Absolute and relative f
requency of innovations per order are also related to two measures of
relative forebrain size in the two zones. The study confirms predicted
trends linking opportunism, brain size and rate of structural evoluti
on. It also suggests that innovation rate in the held may be a useful
measure of behavioural plasticity. (C) 1997 The Association for the St
udy of Animal Behaviour.