How do bird feathers stay dry?

And if the skin now has a hole ...

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The peculiarity of the bird skin is the fletching. The feathers not only serve the bird to isolate and maintain body temperature, to protect against water and to fly, but are also used for social behavior, such as B. at courtship, and important for nest building. Compared to mammals, the skin is - with the exception of the feathered areas - very thin. The feathers develop from skin invaginations, the so-called feather follicles. In contrast to mammals, the bird's skin has no sweat or sebum glands apart from the so-called rump gland located at the base of the tail (the latter are only found in the external auditory canal). A contoured spring consists of the quill, which is divided into the short spring coil and the spring shaft rising above the skin. The feather flag consists of innumerable, fine side branches, which are connected with each other with fine hooks. The individual feathers of the adult plumage can be roughly divided into contour feathers, down and thread feathers. With the contour feathers a distinction is made between the actual cover feathers, the flight feathers and the tail feathers. The down or down feathers are smaller, without hooks and lie under the cover plumage in the adult animal. Powder down is a special form, which breaks down to form a fine dust and is particularly pronounced in cockatoos, gray parrots and pigeons. Thread feathers are found on the eyelids to replace eyelashes, on the nostrils and in the corner of the beak. The change of feathers, the so-called moulting, is strongly influenced by the brood, rearing of the young as well as annual and location fluctuations. The moulting takes place in different rhythms depending on the species of bird. As a rule, the animal remains able to fly and there are no bald spots in the plumage. An increased need for sleep and a reduced resistance due to a 30% increase in energy expenditure as well as increased cleaning of the plumage are observed during this time. The starter moult is a protective reflex of the bird. Mechanical feather damage can often be traced back to incorrect housing conditions such as overly tight cages and overstocking. Secondary damage is also seen as a consequence or accompanying symptoms of serious illnesses, the sick animals sit on the bottom of the cage and for this reason show severely crushed tail plumage.