There are four other main types of feather. Semiplumes are half-way between a contour feather and a down feather. These occur between the contour feathers and help to supply insulation and a certain amount of form as well. Filoplumes and bristles are much smaller. Filoplumes hove only a very few barbs at their tips and are believed to have a sensory function, helping birds keep their feathers in order.
Bristles have practically no barbs at all and are stiff.
They occur around the eyes and mouths of some birds and are protective in function. The fourth main types of feathers are Powder Feathers. These are unusual in that they grow continuously and that they disintegrate at the tip. The barbs breaking down into a fine powder that in Herons at least us useful in mopping up the slime and dust that gets on their fronts during feeding. Thus they help keep the plumage clean.