In Zimbabwe’s Gonarezhou National Park, elephants and reintroduced black rhinos eat the same plants in the same places
Competition from African savanna elephants might make reintroduction of black rhinos unsustainable in the long term in Zimbabwe’s Gonarezhou National Park.
According to Tim O’Connor, who has studied the relationship between herbivores and their resources for over 30 years, the success of black rhinoceros (Diceros bicornis) reintroduction depends on the species’ competition for food with African savanna elephants (Loxodonta africana).
Elephants and rhinos have always coexisted in the area. But in previous decades, elephants didn’t use the park in such high density as they do today. This is partly because in recent years, they have recovered from cullings and drought-induced population drops in the 20th century. In addition, the threat of hunting outside the park’s boundaries in some parts keeps the animals from straying too far.
“While Gonarezhou has been known to have been suitable habitat for black rhinos, it has been heavily impacted by elephants over the years,” said O’Connor, who now works as a contractor for the Gonarezhou Conservation Trust, a partnership between Frankfurt Zoological Society and Zimbabwe National Parks. The trust manages the 5,000-square-kilometer park, home to around 11,000 elephants. “We needed to know, will they have enough food considering there’s a very high elephant population?”
In a recent study published in The Journal of Wildlife Management, O’Connor and his colleagues investigated what black rhinos and elephants were eating within the park during the dry season, when each species heavily relies on woody plants for food.
The research team looked at the dynamics between elephants who have been using the area for a long time at a high density and rhinos that managers reintroduced recently and have a low density.
Black rhinos are native to Gonarezhou but were poached out of the park by 1938. Managers successfully reintroduced them in the 1970s, but once again, poachers pushed them to local extinction. Wildlife managers reintroduced some 29 rhinos again in 2021, sourced primarily from a nearby reserve managed by the Malilangwe Trust, a nonprofit conservation organization.
The rhinos were released into an intensively protected zone, a fenced-in 600-square-kilometer area that takes up about 10% of the park. Wildlifers herded a significant portion of the elephant population out of that zone via helicopter before rhino reintroduction.
“You cannot believe the infrastructure that’s being put in place to protect these rhinos,” said Vernon Visser, a research officer at the Centre for Statistics in Ecology, the Environment and Conservation at the University of Cape Town and a co-author on the study. “It really highlights the cost of keeping rhinos protected in Africa.” Pilots track collared individuals while on-the-ground staff monitor them 24 hours a day.
“The money is both well-spent and carefully spent and important in achieving results,” O’Connor said.
How to identify a rhinoceros bite
To move forward with reintroductions, researchers wanted to ensure that they were releasing rhinos into an environment where they would thrive. In the dry season of 2022, Marileen van der Westhuizen, a master’s student in conservation biology at the University of Cape Town in South Africa, sampled the browsed vegetation of the national park.
Within the plot they were working in, they recorded plant species and signs of predation. To a trained eye, elephant bites on vegetation look different than rhino bites. “The black rhino is known for its distinctive bite,” O’Connor said—they make sharp, clean bites at 45 degrees to the stem. Elephants, on the other hand, are known to rip off leaves and branches. “They aren’t subtle,” O’Connor said.
Between the rugged terrain and climbing temperatures, identifying the plants also proved challenging. Over 400 species of woody plants grow in the park. “These aren’t lovely specimens,” he said. “It’s at the height of the dry season, and they’ve been munched to hell and gone,” O’Connor said.
Browsing preferences
The team analyzed foraging patterns based on soil type, topography, and other environmental and physical factors. Soil type, in particular, dictates nutrient supply. “Nutrient availability is one of the key currencies by which herbivores operate,” O’Connor said.
Topography can also affect foraging of these larger, less agile animals. And plant height matters because elephants are taller than rhinos.
The researchers found that although some elephants were herded out, there were still high levels of elephant activity within the fenced zone. Both species tended to like similar areas when deciding where to browse. In Gonarezhou, the rhinos tended to forage closer to water sources, areas with higher shrub density, and on soils with higher salt content and lower acidity. But elephants also used these areas, and there was a large overlap in foraging height and the species of plants the animals were consuming.
While the large amount of overlap may make it unsustainable in the long term, O’Connor is hopeful about the success of the reintroduction efforts. “The study made us feel very comfortable about the fact that although there is a degree of competition, there’s also sufficient separation and food resources that rhinos utilize that elephants do not,” he said.
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