Feather filaments of birds connect to each other with interlocking hooks.

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“A central shaft carries on either side a hundred or so filaments; each filament is similarly fringed with about a hundred smaller filaments or barbules. In downy feathers, this structure produces a soft, air-trapping fluffiness and, therefore, superb insulation. Flight feathers have an additional feature. Their barbules overlap those of neighbouring filaments and hook them onto one another so that they are united into a continuous vane. There are several hundred such hooks on a single barbule, a million or so in a single feather; and a bird the size of a swan has about twenty-five thousand feathers.” (Attenborough 1981:173)

“Disarranged feathers are carefully repositioned. Those that have become bedraggled or have broken vanes are renovated by careful combing with the beak. As the filaments pass through the mandibles and are pressed together, the hooks on the barbules reengage like teeth of a zip-fastener to make a smooth and continuous surface again.” (Attenborough 1981:179)

Life on Earth: A Natural HistoryBoston (MA): Little, Brown and Company 319 p.October 1, 1981
Attenborough D

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