Rumors of a small bird with an amazing skill have enticed the Darwin team back to the Tama River Triangle, a wildlife kingdom in the Tokyo metropolis. Male streaked fantail warblers literally "sew" surrounding blades of grass together to form a cozy nest for potential mates and offspring. The "thread" used comes from a special spider silk the males specifically seek out. After passing this silk through the grass, the bird bunches up the end to form a kind of knot, ensuring the thread stays put.