![]() ![]() Hooper says sex determination in birds is a little different than in mammals. (Further reading: This yellow cardinal is one-in-a-million.) HOW DOES IT HAPPEN? “Cardinals are one of the most well-known sexually dimorphic birds in North America-their bright red plumage in males is iconic-so people easily notice when they look different,” Hooper says. They likely occur across all species of birds, Hooper says, but we’re only likely to notice them in species where the adult males and females look distinct from each other, a trait known as sexual dimorphism. Gynandromorphs, known as “half-siders” among ornithologists, are uncommon but not unheard of. “This remarkable bird is a genuine male/female chimera,” says Daniel Hooper, a postdoctoral fellow at the Cornell Lab of Ornithology, in an email. ![]() In plain language: Half its body is male and the other half is female. The anomaly is known as a bilateral gynandromorph. “Never did we ever think we would see something like this in all the years we've been feeding,” Shirley Caldwell says. In fact, they weren’t sure they saw it correctly until it came in closer. But the lifelong Erie, Pennsylvania, residents have never seen a creature so wondrous as the half-vermillion, half-taupe cardinal-its colors split right down the middle-that first showed up a few weeks ago in the dawn redwood tree 10 yards from their home. Jeffrey and Shirley Caldwell have been attracting birds for 25 years with carefully tended backyard feeders. ![]()
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