Specifying The Food Desired

Rainbow lorikeets feed on both seeds, which they crack with their beaks, and on nectar which they collect on their brush-like tongues (hence trichoglossus), though they prefer nectar.

To indicate the desire to be fed nectar rather than seeds, some birds will maintain eye-contact with the human feeder, open their beaks, and extend their tongues to their full length.

That is to say, this expression of the instrumental microfunction ('I want it') differentiates the desired object by the bodily action used to process it.