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Yesterday night/morning an animal buried this acorn in my 5th floor balcony flower pot
(sh.itjust.works)
Photo of flower pot with red houseleek and some grass coming out between the remnants of the Edelweiss that died a few months ago and a fresh hole with a single acorn in it.
Yes, other species of Jays would also be capable of doing this.
Thinking about it more, the EU has another more probable species: Woodpeckers.
When I lived in Spain, there were half a dozen woodpeckers who would eat acorns. I have zero doubt that a woodpecker would do this.