nest building: the bird roams around to look for materials, and it works with what it finds. beak by beak, it gathers, then it works. this tendency doesn’t disappear in the cage, yet it can only take place in the tree. we could call all that using a single word and think of it as a single entity, the same way we don’t call a hand a five-fingers-and-a-palm. maybe the one who had the idea of birds as pets lost a limb… in an accident or as punishment? hard to tell.