Red-billed oxpeckers on an impala in Mpumalanga, South Africa

Relationship status: It's complicated

By posing for us, are these red-billed oxpeckers imposing on the impala? Well, science hasn't quite decided on this one. The relationship between parasite-eating birds and hoofed mammals was once considered a textbook example of mutualism, with oxpeckers cleaning up the ticks and fleas that bug the bigger beasts. Which is what we'd like to think is going on here.

But research in the last few decades suggests the oxpeckers only seek out ticks that have had their fill of mammalian blood—making their benefit to impalas and similar animals minimal. So is our impala friend getting a free cleaning or being taken for a ride? We'll let you decide.