TIL: Why do crows rub their beaks?

[timelets]

birds do this for a few reasons. One is to clean off their beaks. The other is to help shape their growing beaks and prevent chips and cracks. The other less studied reason they might do it is to get essential oils from the trees onto their beaks and into their mouths.

https://www.reddit.com/r/zoology/comments/2u76lv/why_do_birds_rub_their_beaks_on_branches/