There are a lot of weeds and things that they will eat and unless they are starving, they will normally avoid what they shouldn't because it tastes bad. Just don't take them out when they are too hungry, at least at first. Sometimes I go around and find field weeds and bring them home for my sheep... They love Purslane, Amaranthus Spinosus (Spiny Pigweed), and wild lettuce, dandelions,thistles of various kinds... If you google these plants you can find pictures of them that will help you identify them. Around a lake, they will eat watercress and wild lettuce, they like any clover type weed if you find some of that growing somewhere and will eat most grasses (horsetail grass is not really a grass at all and is poisonous).