Can I move the com.apple.bird directory to an external drive? I'm looking to save some space on my internal drive and noticed that com.apple.bird takes lots of space - 76 Gb to be exact.

As I understand from What is com.apple.bird? Why does it grow so big? it's part of the iCloud stuff and should only keep the data temporarily. This wasn't true for my machine in the past 3 years. No matter what I did to it it just kept growing to the same size.

Now my question is whether it is safe to move com.apple.bird to an external drive and just create a symlink to the folder on the external drive?
This process contains cache for Apps using iCloud-Backup. Might check to see which applications are using the most space in your Library/Caches/com.apple.bird folder. 

There is a script available here https://github.com/bwesterb/blame-bird to help with that.