Field experiments published in the journal Current Biology have discovered that a species of rhino that is “blind as a bat” rely on their noisy oxpecker neighbors to alert them when humans are nearby. This evolutionary eavesdropping enabled the rhinos to evade detection by humans and even keep an eye on where they were most likely to be.
Black rhinos are currently under threat from organized criminal networks who are poaching the animals in order to trade their horns on the black market. The practice is illegal but hard to police, and uncontrolled hunting has led to a sharp decline in their population.
It’s long been known that rhinos and red-billed oxpeckers are familiar to each other. In Swahili, the red-billed oxpeckers are called Askari wa kifaru, or “the rhino's guard”, as they routinely perch on their backs to get a better glimpse of the environment. These small birds have long red beaks that they use to groom snacks off the rhinos’ hides, such as ticks, flies, and maggots. Beyond grooming, the birds also gain an advantage from being able to see further from the safe, raised position on the rhino’s back, but it wasn’t clear how or if the rhino benefited from its upstairs neighbor.
To test the relationship, researchers from Victoria University, Australia, decided to track the black rhinos with and without red-billed oxpeckers on their backs. They found that black rhinos carrying red-billed oxpeckers were better at avoiding humans compared to their birdless counterparts, with around 40 to 50 percent of those listening in successfully evading humans without detection.
The awareness went even further, as they found that after hearing the oxpecker calls, the rhinos would face downwind, which is the preferred position for hunters trying to avoid being given away by their scent. The number of birds also had an impact on how alert the rhinos were, with a greater number of birds allowing them to spot approaching humans at a greater distance.
It’s possible that this behavior is an adaptive one evolved to protect the oxpecker’s source of food, the rhino, from predation. The rhino benefits from surviving to see another day while the bird doesn’t lose its pantry. The research informs a greater need for conservation in the area, as falling numbers in oxpecker populations will put black rhinos at further risk from poachers.
The powdered horn of rhinos is considered a key ingredient for tonics, treating everything from cancer to hangovers. Their popularity as a pseudoscientific medicinal agent has recently spiked in Vietnam, where owning a rhino horn is also considered a symbol of considerable wealth. They're also a hotly sought target for trophy hunting.
"While we do not know that reintroducing the birds would significantly reduce hunting impacts, we do know oxpeckers would help rhinos evade detection, which on its own is a great benefit," said Dr Roan Plotz, a lecturer and behavioral ecologist at Victoria University, in a statement.
In the paper, the researchers state: “Conservationists might consider re-introducing oxpeckers to rhino populations or re-introducing the two species simultaneously to wildlife reserves to reinstate a proven anti-human sentinel for rhino.”
Oxpeckers aren't the only animals that enjoy riding around on rhino backs.