I heard a great podcast last night about birds and their penises:

https://www.wnycstudios.org/podcasts/radiolab/articles/beauty-puzzle

The gist of it was that once upon a time, 100% of male birds had penises. Some of them evolved these huge long penises and were raping female birds. Female birds were like nope. They essentially stopped breeding with rapist male birds and went for the kindest, most gentle, non-rapey ones.

Now, 97% of male birds only have a hole called a cloacal. And the birds mate by putting their holes together in what's called a "cloacal kiss." Sperm can't enter a female unless she cooperates and turns her cloaca inside out. If she doesn't budge, fertilization won't happen. Female birds can also keep the sperm inside her body for quite some time until conditions are right for her to have baby birds.

Female birds demanded gifts and effort and good looks and good nest building and co-parenting. That's how most modern birds are when it comes to mating. The female birds call all the shots. Also why male birds are generally so colorful and pretty, with fancy plumage, dancing and singing, while female birds can look drab in color.

None of the material I've read talks about why female birds get all this privilege, but I had a shower thought: it's because birds can fly. Female birds can just fly the hell away from an asshole male bird and not mate.

Female choice is so powerful that it can remove penises from almost an entire species. Knowledge is power, ladies!