The oxpecker and the rhinoceros go for a ride
They hitchhike on the backs of black rhinoceros, but red-billed oxpeckers are doing more than just catching a ride across the African savannah.
Research by Te Herenga Waka–Victoria University of Wellington PhD graduate and rhinoceros expert Dr Roan Plotz shows the birds, called Askari wa kifaru in Swahili, meaning “the rhino’s guard”, are actually communicating indirectly with the rhinos.
The birds’ cries of alarm when a predator, especially a human, comes near can encourage the rhino to face downwind–their “sensory blind spot”–and assess the danger for themselves.
Dr Plotz, now a lecturer in environmental science and behavioural ecologist at Victoria University in Melbourne, is lead author of the research, which was recently published in Current Biology journal. He is one of the world’s foremost rhinoceros observers.
In the study, the research team discovered that black rhinos giving a lift to oxpeckers, which eat insects and parasites on their hide, were much better at sensing and avoiding humans than those without passengers.
Dr Plotz, who was born in South Africa, says the rhinos are “as blind as a bat” and hunters, if downwind, can get as close as five metres away.
The research was carried out while Dr Plotz was a PhD student at the University in Wellington under the supervision of Associate Professors Wayne Linklater and Peter Ritchie in the School of Biological Sciences. Professor Linklater is now at California State University in Sacramento.
Dr Plotz says for his PhD he was keen to go back to Africa where he grew up.
“An opportunity presented itself for ongoing rhino research because Wayne had been doing post-doctoral work there for several years.
“It was a perfect fit–I had become an ecologist because I spent my time as a child going to game reserves and seeing these mammals.”
Dr Plotz finished his Wellington PhD in 2014, after spending three years in Africa tracking rhino. “Our study was in a game reserve called Hluhluwe-iMfolozi Park in the northeast corner of South Africa in an area called Zululand. Between 2007 and 2010 I tracked rhino to study their behaviour and interactions with species like oxpeckers.
“While studying the park’s rhino we noticed the alarm calling by oxpeckers on rhino. We predicted that, if the birds were acting as an anti-human sentinel for the rhino, the ones we were able to see out there in the landscape should have very low numbers of oxpeckers on them–because if the birds were telling them the humans were coming, the ones with the birds on the backs should be able to avoid us.”
Dr Plotz only found birds on the backs of rhinos on 17 occasions out of 100 searches.
“During my PhD, I was able to put horn-implant radio transmitters into the horns of 14 black rhino. Because we could then approach these tagged rhino undetected, and creep up and avoid detection right until the last little bit, we realised we could use them as a control to better estimate how many oxpeckers are on rhino more generally.
Their research suggested oxpeckers are generally present on black rhino for about half the time. “Because we found it so much harder without radio telemetry to find rhino with oxpeckers on their back, this strongly suggested that untagged rhino with oxpeckers were avoiding us altogether.”
The team tested this with human-approach trials. “In only 23 percent (11 out of 48) of approaches without the birds on the back did they detect my colleague, Bom Ndwandwe, who approached from a cross-wind direction with a laser rangefinder to measure how close he could get before being detected. But with the birds on their backs, rhino detected his approach every single time.”
Dr Plotz says it is still not known if the birds are calling specifically for humans or whether they do the same for lions, hyenas and other threats.
“We also don’t know that oxpeckers are alarm-calling on behalf of the rhino or for themselves. Whichever way it is, the rhino have learnt to eavesdrop on the birds’ alarm calls, presumably in response to their vulnerability to humans.”
The number of critically endangered black rhino has risen since about 1990, at which time it had dropped as low as around 2000. There are now around 5000, but poaching is still an ever-present danger.
“Unfortunately there has been a recent poaching spike again. We’ve shown clearly that, at the very least, the birds help rhino avoid and/or improve detection of humans, and while we don’t know if it will stop poaching pressure, we do know that the birds will at least make it a lot harder.”