Many studies on the efficiency of feeding in finches
concentrate on husking time in relation to average seed
size and bird size. Large species are capable of eating
larger seeds and are able to husk large seeds faster than
smaller species. It is generally assumed that husking time
is related to bite force. However, there are very few studies
that investigate the relationship between husking time,
seed hardness and bite force directly.
In our experiments we measured the seed husking time
and the maximal bite force of two taxa of seed cracking
birds. Husking time is related to maximal bite force in a
highly non-linear way and differs between estrildids and
fringillids. Fringillids with the same bite force as estrildids
take less time to crack seeds, but only when the strength of
the seed coat is close to their maximal bite force. For seeds
that are relatively soft the difference in husking time
becomes very small. A preliminary jaw motion analysis
provides evidence that this difference in husking time
between estrildids and fringillids is paralleled by a
difference in husking technique. This difference in
technique does not affect bite force as such, but decreases
the chance of failed cracking attempts.
The selective advantage of a small increase in maximal
bite force may be related more to the decrease in husking
time for seeds with hardness below the maximal bite force,
than to the increase in range of seed hardness that the bird
is able to crack.
Key words: bite force, feeding performance, seed hardness, jaw
movement, finches.