I was curious, so I analyzed the geometry of the peacock's tail-feather display. Turns out the shape is a symmetrical phyllotaxis, which is somewhat surprising. Most phyllotaxis patterns in nature (like on pinecones, pineapples and sunflowers) have spirals of adjacent Fibonacci numbers (usually 5, 8, 13 or 21), but the peacock's feathers have the same count of spirals in both directions!
83