Width of the distal portion of the gnathothecal tomia (tip of lower beak) in six species of Macrolobium-eating psittecines.

The six species that eat Macrolobium fruits use thier lowe mandibles as a gouge to open fruits and access seeds. Feeding activity leave marks on the hard fruits.

These measurements show that the means of the end o the lower bills are different and that there is very little overlap in range, so, if you have a fruit with a parrot bill mark on it, you can tell wich species was responsible (at least in this case)