What makes birds two-sided like this, both male and female in the same body?
It’s a very rare condition and it only happens when there’s an embryo error in the bird’s sex chromosomes, W and Z. The resulting oddity is a “bilateral gynandromorph.”
Learn how it occurs in this last-day-of-the-year article … Anatomy: W and Z
(photo credits: evening grosbeaks at the Smithsonian by ap2il via Flickr, Creative Commons license. Northern cardinal courtesy of Western Illinois University. Click on the captions to see the originals.)
Fascinatingly strange. Thanks, Kate
Off-topic, but WOW! Just now, a bluebird at my heated birdbath. No, not a bluejay, an American Bluebird. Poor thing, he must be cold.