Flying around Northern Illinois is a very pretty bird with unusual colouring. The cardinal is half red, half drab grey. That's because it is a very rare split-sex gynandromorph, being half-male, half-female. It's also very lonely. Researchers from Western Illinois University observed the bird for several weeks, and it kept to itself a lot of the time. "The bird never paired with another cardinal, and the team never heard it vocalizing," reports iflscience.com. The team also noticed "unusual agnostic behaviors" from other birds.
While most mammals have XY or XX chromosomes and the release of hormones to determine gender, birds "have a ZW sex determination system--with females having ZW and males being ZZ--and hormones don’t play nearly as big of a role." In 2003 a study of a group of zebra finches discovered that the birds' brains "were literally half genetically male and half genetically female," and that "the sex differences were neural in origin, and not gonadal." This is all fascinating, but it doesn't really cheer up the cardinal, does it?
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