Many a frustrated birder has griped about the difficulty of telling the neotropical black-chinned tanager from its neighbor, the blue-winged tanager. “It’s just slight color variation on the back,” said Robert Bleiweiss, a zoologist at the University of Wisconsin-Madison. But new research shows the visual differences are greater than those that meet the birder’s eye. Indeed, if you hold them up to an ultraviolet light, the bird species become recognizably different.
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