Tomato leaves, eggplant leaves and all of the brassica family can be harmful to ducks. This is from a vetinary textbook I have on poisonous plants with reference specifically to animal groups. So that includes cabbages, broccoli, bok choi, cauliflower etc. Obviously it would be in larger amounts or build up over time. I have chosen not to feed anymore after having sick ducks with no other explanation.