Filoplumes have a long shaft with a little tuft of barbs at the end. There are usually two associated with each contour feather. They probably serve a sensory function, letting the bird know if the contour feathers are lying flat or are twisted. They may be 1/2-2 cm long. On many songbirds the filoplumes on the back of the neck stick out beyond the contour feathers and can be seen if you look closely. They can often be seen on fresh chicken wings from the grocery store.