Mine too, though when the tomatoes were in season they preferred them to the grapes.My girls absolutely love grapes and tomatoes. They also love canned corn especially cream style. I purchase no salt.
Today they got cut up grapes, pear cores, and a little shredded Gouda. Then I cut the small oldest leaves from my collards plants and the chickens LOVED them, grabbing beakfuls of leaf as fast as they could, then swallowing them.
One of the Dominiques ran out the run door when I opened it, and tried to eat some weed leaves. She came right back when she realized the others were getting treats inside the hoop coop!