As cute as tuxedo-patterned penguins would look sporting oversize loafers, footwear is not part of the dress code for these warm-blooded birds. Bare feet prevent these stately ice emperors from burning up in their suits.

Most of the penguin body is kept cozy by its warm, waterproof plumage. Beneath the skin, blubber adds to the insulation. Together, fat and feathers work so well that a careless bird might overheat on a sunny day. The naked beak and feet allow heat to escape, helping the body to maintain a steady temperature.

A little biological ingenuity keeps the extremities from icing over. Certain arteries in the penguin leg can adjust blood flow in response to foot temperature, feeding the foot just enough blood to keep it a few degrees above freezing.

Not that all species need such a system—on the equator, Galápagos penguins contend with sweltering sun and heat with much help from their cool feet.

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