They'll eat the fruit, I know people who keep chickens in their green houses to take care of the slugs, the birds eat the tomatoes but less of them than the slugs. Don't know anyone who's lost a bird to tomato leaves though. Mine even ate a fox glove plant and where fine. The toxins in tomato plants block digestive enzymes in insects I don't know if it would have the same effect on chickens unless they ate a lot of the leaves. Plus if there's something better around like lettuce or kale or bugs they'll choose those instead. My ducks never touched the tomatoes just the squash leaves and borage, same with my bantam hen she never touched the tomato greens.