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Bird's eye is a type of figure that occurs within several kinds of wood, most notably hard maple. It has a distinctive pattern that resembles tiny, swirling eyes disrupting the smooth lines of grain. It is somewhat reminiscent of a burl, but it is quite different: the small knots that make the burl are missing.
It is not known what causes the phenomenon. Research into the cultivation of bird's eye maple has so far discounted the theories that it is caused by pecking birds deforming the wood grain or that an infecting fungus makes it twist. However, no one has demonstrated a complete understanding of any combination of climate, soil, tree variety, insects, viruses, or genetic mutations that may produce the effect.
Bird's eye maple is most often found in Acer saccharum (sugar maple), but millers also find bird's eye figures in red maple, white ash, Cuban mahogany, American beech, black walnut, and yellow birch. Trees that grow in the Great Lakes region of Canada and the United States yield the greatest supply, along with some varieties in the Rocky Mountains. It is not uncommon in Huon Pine, which grows only in Tasmania. Although a tree's bark may offer a few clues that indicate the lumber might have bird's eye figure, felling the tree and cutting it apart is necessary to know for sure.