Sexual dimorphism — differences in appearance between males and females — tends to be very visible in birds. Think of a rooster and a hen, or a peacock and a peahen: Females that spend a lot of time nesting need good camouflage, while males have a real need to show off. In the field, it can sometimes be easy to dismiss a male and a female of one species as being two separate species altogether, but in the case of this half-male, half-female cardinal, plumage dimorphism is impossible to miss.
Images via Why Evolution Is True
These photos were submitted to Jerry Coyne, an ecology professor at the University of Chicago, for his great Why Evolution Is True blog. The bird in question is a gynandromorph, or an organism that displays the characteristics of both a male and female. Gynandromorphy in many species is due to chromosomal anomalies, as Coyne explains. But birds have a different chromosomal arrangement, which means this type of bilateral gynandromorphy is still a bit of a mystery.
Update: Thanks to Twitter, I found a great post that explains bird gynandromorphism more in depth, but it also looks like this cardinal might be showing pigment loss, rather than being a gynandromorph.
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