Check out this website http://science.jrank.org/pages/3421/Hummingbirds-Biology-hummingbirds.html
After many years of pressure and possibly heat it will be compressed back into a form of rock such as sediment.
hope this helps
I do think that they close to not allow too much of either water or air from entering.
the hollow tube allows water to flow easily.
https://www.bbc.co.uk/bitesize/guides/z28g7p3/revision/1
