Rooks

Hi, I wonder if anyone else has noticed that rooks have a pouch just under their beaks which fills up with any food they are eating, presumably so that they can transport it back to feed their young at this time of year?  We get several in our garden feeding on fat balls and I noticed this for the first time recently, thought the bird was deformed at first until I saw what was happening. 
Hope someone else has noticed this as I can't find any information anywhere else about it.

Hello from Cornwall.