Oxpecker and Bison
Bison
A bison is a big mammal that has a bad tick problems and lets birds pick them off of it.
Oxpecker
The ox-pecker is a bird that goes around and eats ticks and fleas off of mammals.
How a bison and ox-pecker help each other
A bison and ox-pecker help each other when the ox-pecker eats the ticks on the bison and gets a good meal from all of the ticks.