The Oxpecker mainly feeds on parasites that suck blood, like ticks and fleas, they can be seen riding on the backs of hoofed animals such as buffalo, rhinoceros, warthogs and giraffe. Whilst feeding on parasites from open wounds on the animal. They are also known to peck at animals to create a wound to suck some blood.
There appears to be a symbiotic relationship between the Oxpecker and hoofed animals, with the Oxpecker providing a wound cleaning service to the animals. The fact that they essentially feed of another living organism could also classify them as a parasite.