![]() In short: most mesoptile feathers don’t sprout from natal down pores. Having said that, we don’t know if the small, shallow follicles that produce natal down die to make way for new follicles, or enter a resting phase in which they restructure themselves to grow juvenile or adult down. So feathers don’t sprout from pores that produce down. We know that follicles with smaller diameters produce down, and follicles with larger diameters produce all other feathers, although follicular size, shape, and complexity may vary in accordance with the size, shape, and complexity of the feathers the follicle grows. While an eaglet’s thermal down appears, well… downy, it includes down and downy-looking precursors ( pennaplumae) to wing, tail, contour, filoplume, and semi-plume feathers. Does thermal down sprout from natal down pores?įor the most part, no – but it’s complicated. ![]() Most juvenile feathers emerge from the same pores that produce mesoptile feathers, although it’s unclear whether all down feathers do. What we call juvenile feathers – the fully-formed feathers that begin to replace mesoptile feathers between roughly 20 and 28 days of age – are also known as juvenile feathers to people who research feathers, although any given species of bird may have more or fewer stages between natal plumage and juvenile feathers than the one stage that bald eagles have. In altricial birds like bald eagles, follicles that become active after hatch can grow down or specialized feathers. Nestling eaglets grow feathers three times – once in the shell and twice after hatch – and molt them twice. As the name suggests, mesoptile feathers are intermediate feathers – more complicated than the natal down they replace and simpler than the juvenile feathers that will replace them. While we don’t see mesoptile feathers right away, mesoptile feather germs ‘wake up’ and begin the work of assembling feathers shortly after hatch. What we call thermal down – the greyish plumage that begins to replace neoptile feathers at about eight days of age – is known as mesoptile feathers to the same people who call natal down neoptile feathers. In altricial birds like bald eagles, follicles that become active prior to hatch can only grow down. Those that do produce natal down, which is symmetrical, uniform, and general in purpose. ![]() All feather follicles develop in the egg, but in altricial birds like bald eagles, most follicles don’t activate prior to hatching. What we call natal down – the adorable fluffy white plumage that covers hatchling eaglets – is known as neoptile feathers to people who research feather development. April 28, 2022: Happy 22 day, DH2! DH2 weighs about 3.3 pounds and its footpad is about four inches long. ![]()
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