Black rhinos (犀牛) have terrible eyesight. Even so, these large African animals can fight against hungry lions and hyenas. With big sword-like horns, their large and thick-skinned body plan has proved to be good enough to survive in a place full of huge predators (捕食性动物). But those protective features are no match for humans with guns.
Today, the species is seriously endangered largely due to illegal hunting. But the rhinos may have an unlikely partner against hunters: the red-billed oxpecker (牛椋鸟). The chatty, sociable birds often hang out on the backs of rhinos, feasting on the ticks (虱子) on their bodies.
"And actually, research has shown that the tick is the favorite diet of an oxpecker. And if they feed on ticks, that is a good thing," said Plotz, a behavioral ecologist. He suspected that the rhinos put up with them because the oxpeckers make loud alarm calls whenever they see humans approach-giving the rhinos an early warning to flee.
To test whether the oxpeckers do, in fact, act as noisy lookouts, Plotz and his team placed radio transmitters (发送器) in the rhinos horns. The researchers found that rhinos without oxpeckers detected an approaching human only 23 percent of the time, at an average distance of 27 meters. But when oxpeckers were present, the birds warned the rhinos 100 percent of the time. And they sensed the human 61 meters away on average. And the more oxpeckers on the scene, the greater the detection distance— which means the earlier the warning.
It makes sense because the more eyes you have on your back, looking out for you, the more chance that you can pick up anything coming. What we think is going on, fundamentally, is that the rhino is listening to the alarm call. There can be no doubt of that. Listening to oxpecker alarm calls brings a really strong anti-human benefit.
Plotz thinks the oxpeckers may have gradually changed and developed their behavior because it protects their convenient food source. And the more lookouts, the better in what seems like a win-win for both species: the birds thrive and the rhinos survive.
