nearly all piciformes have parrot-like zygodactyl feet—two toes forward and two back, an arrangement that has obvious advantages for birds that spend much of their time on tree trunks. an exception are a few species of three-toed woodpeckers. the jacamars aside, piciformes do not have down feathers at any age, only true feathers. they range in size from the rufous piculet at 8 centimetres in length, and weighing 7 grams, to the toco toucan, at 63 centimetres long, and weighing 680 grams. all nest in cavities (holes) and have altricial young, meaning they have to look after their chicks for quite a long time.