We've lost some of our hazelnuts.
To the juvenile Greater-Spotted woodpecker [and he'll become a Greater-Splatted if I lay hands on him!] we've seen around... or to the Nuthatch we've heard.
Seriously though, the method seems to be as follows...
Rip a bunch of nuts from bush and drops down onto the concrete base rail of the fence.
Use this as an anvil....
|Anvil & nuts
but [and this is where the "symbiosis" aspect comes in] he doesn't get much of a meal, as the noissettes are still very unripe and absolutely tiny.
[And they'll probably stay small unless we get some rain.]
So he leaves them where they are.... and our little rodents come along and find that someone has supplied some nuts for them.
So we've got a bunch of nuts that have a couple of hammered openings with nuts that have been chewed open.
This is all purely conjecture as I haven't seen the woodpecker or nuthatch at work... I am going on the evidence.