Another example of cranial kinesis
We've had a few threads before on BPN showing images of the extreme tip of the upper bill of various shorebirds bending upwards. This is an example of rhynchokinesis. Rhynchokinesis is a particular type of movement in the general class of skull bone movements called "cranial kinesis", which just refers to skull bones moving in relation to each other. Perhaps the best example of cranial kinesis is shown by snakes when they have to swallow a big prey item.
I thought I'd show what gannets can do by way of cranial kinesis. Quite infrequently, they show a stereotypical behaviour akin to a yawn where they open their gape to it's fullest extent and then bend their upper mandible upwards like the image shows. The gannet skull has a hinge of thinner bone at the base of the upper mandible which allows it to do this.
I'll post a "yawn" sometime today in Avian.
It would be interesting to see examples of this from other species.
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