Green acorns contain high levels of pyrogallol. Don't ask me what that is, I'm not a chemist. What I do know is that the pyrogallol is poisonous to pigeons (as well as horses, and probably a variety of other birds and mammals.) Young pigeons seem most susceptible, possibly because they're small and still developing. They have less body mass relative to an adult. And young pigeons are still learning the 'food' vs. 'not food' life lesson. Too many acorns is definitely 'not food' for pigeons.
I found this young squab in the middle of the road, staggering about, and too disoriented to escape my slow, lumbering approach.
He still has baby fluff, and you can see all the feather casings he's shedding onto my plaid shirt. He's not yet grown into his beak so he's quite young. I've put him in a spare broody coop overnight to protect him from hungry foxes and village cats. He may live, he may not (my record for rehabilitating baby birds has been 0 for 3 this year). If he doesn't, we'll do a post-mortem and see if, in fact, he has a cropful of acorn shells.
I hope he's simply recovered enough to fly away, and smart enough to head for the barley fields instead of the woods for his breakfast.