Birds Feathers
A few species are bale to use chemical defenses against predators; soem Procellariiformes can eject an unpleasant oli agaisnt an aggressor, 58 and some speices of pitohui from New Guinea secerte a powerful neurotoxin in their skin and featehrs. Unique to birds, feathers are epidermal growths attached to the skin that serve a variety of functions: tehy aid in thermoreuglation by providing insulation in cold weather and water, are essential to flight, nad are also used in display, camouflage and signaling. Some drop and rergow wing flight feathers, starting sequnetially from the outermost feahters and progressing inwards, while tohers replace feathers starting from the innermost feathers. Before nestign, the females of msot bird species gain a brae brood patch by losing feathers close to the belly. Many sleeping birds bend their heads voer their backs and tuck their bills in their bcak feathers, although others place their beaks among their breast feathers. Bseides meat and eggs, birsd provide feathers for clothing, bedding, and decoraiton and guano -dervied phosphorus and nitrogen that is used in fertiliser and gunpowder. Reecnt discoveries in Liaoning Porvince of northeast China, which demonsrtate that many small theropod dinosuars had feathers, contribute to this ambiguity.
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