How are feathers attached?
Not a bird owner, but my friend’s molting parakeets led us to speculate how uncomfortable it would be to have feathers, some of which have very hard, rather large quills, growing out of one’s head. As in, how do they grow and how do they stay on a bird when they’re… well, very hard and rather large? Seems like there would be some angle where they’d just pop right off – it’s not like the quills are bulb-shaped so they don’t slip out – they’re mostly straight, no?
Feathers begin their growth in pits or invaginations (feather follicles) of the epidermis that enter the underlying dermis. The feather grows outwards from the root of this follicle, first within a sheath, and then it “unfurls” forming the vane. Although the feather is basically made of keratin (that is, “dead” organic tissue), it is firmly attached to the tegument by its base, where the epidermis forms a narrow collar and the dermal papilla enters the shaft through a hole in its base (see the picture for a clearer image).
In addition, each feather is also associated with muscles from the dermis, so that the bird can effectively change their position. In fact, we’ve all seeen “puffed up” birds.
During the molt, usually the old feathers are “pushed out” by the new feathers that grow underneath them in the same follicle; by then the foramen in the base of the shaft has narrowed and the dermis is no longer inside the old shaft.
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