Answer:
They are all vertebrates: Females have two lateral vaginas, which lead to separate uteruses. A third canal, the median vagina, is used for birth. Males have a two-pronged penis, which corresponds to the females' two vaginas. The penis is used only for discharging semen into females, and is separate from the urinary tract. Birds have unique modified immune system that fights off bacteria found in seeds and plants.
Feathers. Many other animals have developed flight. Many other animals have hair, skin, scales, or fur but none have been able to attain the physical characteristic of feathers.