Our results provide direct evidence that in both estrildids and
fringillids husking time is directly related to bite force and that
husking time decreases exponentially with increasing bite
force. To get a good estimate of the relationship between bite
force and husking time we aimed to collect data over the whole
range of bite forces within the two families investigated.
Unfortunately we were not able to find an estrildid species
large enough to crack hemp very easily, and to confirm
experimentally the estimate of minimum husking time. For a
few species only one individual was measured. However, the
interspecific variation in husking time is much larger than the
intraspecific variation. This is illustrated by the analysis of the
data according to a nested ANOVA design (individuals nested
within species, and species within family). For the species for
which more than one individual was measured it shows that
intraspecific variation of the ln transformed data is only 4% of
the total variation (restricted maximum likelihood estimate),
and that variation between species is 13 times larger than
intraspecific variation.