sort by best latest
I agree with Teresa.
This habit was also observed in the dynasaurs, which proves that birds are their direct descendants :-)
You can help the HubPages community highlight top quality content by ranking this answer up or down.
It helps them digest their food - the pebbles help grind some items of food.
Copyright © 2017 HubPages Inc. and respective owners. Other product and company names shown may be trademarks of their respective owners. HubPages® is a registered Service Mark of HubPages, Inc. HubPages and Hubbers (authors) may earn revenue on this page based on affiliate relationships and advertisements with partners including Amazon, Google, and others.
Copyright © 2017 HubPages Inc. and respective owners.