I actually watched my comet chicken jump up and pick off holly berries and all 5 chickens scratch all around a big holly tree. Funny thing, 2 of my chickens were acting ill - I could not figure out why and thought they were really sick - look almost drugged. I'll never know if it was the Holly tree but it's the only thing I could associate w/their illness.
I had set up a forage area several weeks ago that included 2 areas under a dogwood and holly --- I was really worried when 2 of the chickens were acting the same sick way - standing w/tails down, egg yolk poo --- still eating and drinking but not as much. I thought perntonitis but I had another chicken euthanized from that so know a bit about that. I find it unlikely that both chickens would come down w/that 3 days apart. It seemed more like a toxin or virus.
They both seem to be improving after a week and I don't allow them under the Holly - we'll see ------