Here's why:
* Rhinos are large and imposing: They don't typically have many birds that perch on them.
* Birds are opportunistic: They will perch where they find safe, elevated spots.
* African birds: Some birds found in the same habitats as rhinos might occasionally perch on their backs, but there's no specific association or name for such a bird.
If you're thinking of a specific bird, please provide more information about it.