It was the year when the Serengeti National Park’s music, or at least one section in its chorus-of-the-wild, died. In 1991, the twitters and whines of African wild dogs went strangely silent in Tanzania’s iconic protected area.
Scientists began tracking wild dogs, also called painted wolves, here in 1964. Over the next quarter-century, researchers watched as the wild dog population dwindled, then disappeared. Why did these canids effectively go extinct in a land where gazelles and other prey were plentiful?
Could the biologists themselves somehow be responsible?
The blame game
It’s anathema to researchers to think their actions might cause harm to an endangered species like the African wild dog. But in 1994, Roger Burrows of the University of Exeter unleashed the controversial idea that it was indeed scientists’ actions that led to the dogs’ demise.
Wild dogs became stressed, Burrows stated, when researchers immobilized and placed radio collars on them. The stress suppressed the wild dogs’ immune systems, he said, allowing diseases they already carried to kill them.
Burrows’ hypothesis rattled biologists who had long depended on radio collars to follow animals, especially endangered species. The implications went far beyond the Serengeti, say ecologists Craig Jackson of the Norwegian Institute for Nature Research, Eivin Roskaft of the Norwegian University of Science and Technology and colleagues at the Tanzania Wildlife Research Institute and Carnegie Institution for Science.
The team recently published a paper debunking Burrows’ thinking in the journal Ecology and Evolution. Serengeti wild dogs, the researchers found, weren’t the victims of science.
Life on the periphery
Although Serengeti National Park was, and is, without wild dogs, the dogs survived in the park’s outskirts. These outlier wild dogs have been studied since 2005. Many are outfitted with GPS collars; data show that the dogs sometimes briefly cross park boundaries. “Therefore, wild dogs could reside there,” says Roskaft. But they don’t.
There are now more than 100 wild dogs in 10 packs outside the park in the Ngorongoro Conservation Area and Loliondo Game Controlled Area. Between 2006 and 2016, Roskaft and colleagues report, 121 wild dogs from these locations were handled by researchers, with 45 of the dogs radio-collared.
How many of the 121 survived for a year or more afterward? Some 87.6 percent, or 106 wild dogs. Scientists’ “interventions did not evoke disease outbreaks, and the high survival rate does not support Burrows’ hypothesis,” the biologists write in their paper.
Ecologist Craig Packer, a National Geographic Explorer and director of the University of Minnesota Lion Research Center, has studied lions in the Serengeti for more than three decades. Packer, who was not involved in the study, agrees with its conclusions. “This paper,” he says, “nails the coffin on the whole debate.”
In: Hyenas and lions. Out: Wild dogs.
More than 25 years after wild dogs vanished from Serengeti National Park, none roam its grasslands. The answer, ecologists believe, is also the reason the dogs first faded away: hyenas and lions.
Rather than an extinction, Roskaft says, wild dogs’ disappearance was a shrinking of their range in response to increasing numbers of hyenas and lions. These carnivores often scare wild dogs away from their food.
The dogs moved out to the “far suburbs” — hillsides to the east of the park. The hills may offer safe places for wild dogs to den and raise their young.
With wild dogs out of the way, hyena and lion populations boomed. Any wild dogs brave enough to stay were left with slim pickings.
The evidence is clear, says Roskaft. “Increasing competition from hyenas and lions likely led to the downfall of the Serengeti National Park wild dog population.”
Packer and colleagues came to a similar conclusion. Between 1966 and 1998, the park’s lion population nearly tripled, they found, and wild dogs declined. Wild dogs once occupied park areas with low numbers of lions, which the dogs abandoned as lions “saturated” the region.
A seesawing Serengeti
The picture was once very different. In the 1960s, Serengeti National Park was recovering from the effects of rinderpest, a disease of cattle that infected ungulates such as wildebeest and buffaloes – lions’ prey. The park’s lion population declined, and its wild dogs increased.
As rinderpest was brought under control and ungulates returned, lions followed. Soon wild dogs were edged out.
“A large number of wildebeest and lions, however, is a more ‘natural’ state for the Serengeti than the conditions that once allowed wild dogs to occupy its plains,” says Packer.
The big puzzle, he says, “is why wild dogs are able to co-exist with lions in places like the Selous Game Reserve in Tanzania and Okavango Delta in Botswana. We suspect there’s something about the habitat that provides the dogs with ‘safe spaces.'”
With more answers needed, Roskaft is happy to put an end to the conjectures about radio collars. “Tools that help us understand endangered wild dogs and other species are important to protecting these animals,” he says, “especially in a world where carnivores are struggling in the face of a growing human population.”
No wild dog twitters and whines wend across Serengeti National Park. But, says Packer, “effective conservation requires multiple locations since species cannot always co-exist in all circumstances.”
To wild dogs traversing the Serengeti: at least for now, your melody is perhaps better sung in the savanna next door.