Red-billed oxpeckers hitching rides on the backs of black rhinos are a common sight in the African bush. The birds are best known for feeding from lesions full of ticks or other parasites on a rhino’s hide. But new research suggests that the relationship between the two species is much more mutualistic (SN: 10/9/02). Shouty and shrill oxpeckers can serve as an alarm bell, alerting black rhinos to the presence of people, scientists report April 9 in Current Biology. That could help the endangered animals evade poachers, the researchers propose.

“Rhinos are as blind as bats,” explains Roan Plotz, a behavioral ecologist at Victoria University in Melbourne, Australia. Even in close proximity, a rhino might struggle to notice lurking danger by sight. But the oxpecker easily can, unleashing a sharp call to warn of intruders.

In South Africa’s Hluhluwe–iMfolozi Park, Plotz and his colleague Wayne Linklater of California State University, Sacramento approached 11 black rhinos (Diceros bicornis) by foot on the open plain on 86 occasions. The team found that those rhinos with a red-billed oxpecker (Buphagus erythrorhynchus) tagging along were much better at detecting the researchers’ presence than those without.

“Rhinos without oxpeckers on their back were able to detect our approaches just 23 percent of the time whereas rhinos with oxpeckers detected them every single time,” Plotz says. Rhinos listening to an oxpecker’s heads-up also picked up on the approaching scientists from 61 meters away, more than twice as far as when the rhinos were alone.

The red-billed oxpecker serves as an alarm bell for black rhinos, signaling nearby danger. The birds often eat pests like ticks from the backs of rhinos and other mammals, including livestock. Due to the practice of applying pesticides to livestock, the oxpecker has seen its numbers decline. Jed Bird

All rhinos responded to the oxpeckers’ alarm calls by becoming vigilant — standing up from a resting position, for example — and turning to face downwind, their sensory blind spot. The rhinos then either ran away or walked downwind to investigate the potential danger.

Black rhinos were once the most numerous species of rhino in the world. But poaching for traditional Chinese medicine has devastated the species (SN: 11/17/79). Though poaching has slowed since its peak in 2015, just 5,500 black rhinos remain in the wild and conservationists are searching for solutions that could permanently protect the critically endangered species.

The red-billed oxpecker has also declined. The birds feed on ticks, including those burrowed in cattle, but for decades, farmers treated their livestock with pesticides to kill the parasites. This inadvertently transferred the poison to oxpeckers, causing them to die out in some regions in Africa. In turn, many black rhinos must navigate the landscape without their avian companions. Given the study’s findings, Plotz thinks conservationists should consider reintroducing oxpecker sentinels to rhino populations.

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“The oxpeckers are clearly adding a new depth and dimension to rhino awareness levels,” says animal ecologist Jo Shaw, Africa rhino program manager at World Wildlife Fund South Africa. “This emphasizes further the complex webs between species within ecosystems and the need for conservationists to work to ensure all functions remain intact.”

However, wildlife ecologist Michael Knight, chair of the International Union for Conservation of Nature’s African Rhino Specialist Group, cautions that a lot of poaching takes place during full-moon nights when sleeping oxpeckers would be of less assistance.