[mcbits]

That points to a well developed individual memory. I don't think they're using the locations of nuts to encode knowledge for each other and future generations. (If they are, that's tremendous.)

But imagine if the birds also carved symbols into tree trunks and taught their friends how to interpret the symbols to find hidden caches of nuts, or to share techniques for building more durable nests, etc.

Written language allows us to store, access, and share information beyond our individual memory limits. It is sort of a collective memory as well as an expansion of individual memory. I can write down the locations of 21,000 nuts, and I can hand that book off to you.