Why did the bird go to the hospital?

Not unaccompanied.

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EDIT: Of course! Although, some veterinary clinics may only take specific cases, such as household pets or farm animals. Different vets specialize in different groups of animals, but I think that many clinics will take in a bird, whether it be an injured hawk that needs medical care or a cockatiel that won't eat. Vet clinics accept a wide variety of cases because you shouldn't turn down an animal in need, even birds!