The Red-billed Oxpecker, also called a “Tickbird” because its diet consists mainly of ticks residing on the bodies of large mammals has an interesting relationship with those mammals. On the one hand it eats the pesky ticks, but it also sometimes tends to keep poking at existing tick bites, making them bigger looking for food. These mammals on the other hand can survive without the Oxpecker whereas the Tickbird is heavily dependent on on the mammals for food. There is an interesting debate on whether their relationship is mutualism or parasitism.
Red-Billed Oxpecker on a Giraffe