Solving the mystery of Serengeti's endangered wild dogs

In 1991, a strange thing happened in the wilderness of Serengeti National Park in Tanzania.

The Serengeti World Heritage Site is home to a spectacular array of carnivores, cheetah lions and more. And with more than a million and a half zebras, wildebeest and gazelles migrating annually through the park, there is plenty to eat.

One of the least known predators of the park is the African wild dog, Lycaon pictus. They are not pets of the family, but an entirely separate species. Researchers began looking for the number of wild dogs in 1964 and, over the years, have observed a decrease in the number of wild dogs in the park.

But in 1991, the dogs simply disappeared from the plains of Serengeti and a huge scientific debate ensued.

Why did wild dogs in the park suddenly disappear?

Blame the researchers?

In 1992, a British researcher, Roger Burrows, had put forward a controversial hypothesis: it was the researchers themselves who led to the deaths of the dogs.

The "Burrows Hypothesis", as it was called, suggested that wild dogs were stressed when the researchers immobilized them and put on radio collars.

This stress resulted in the suppression of the animal's immune system, suggested the hypothesis, which then allowed the rabies hidden in their blood to kill them eventually. This badumption has shaken the world of conservation, which has used tools such as radio collars to detect critically endangered and often elusive species.

Since Burrows put forward his controversial hypothesis for the first time, the debate continues to rage.

"The consequences of this hypothesis go beyond wild dogs in the Serengeti," said Craig Jackson, a researcher at the Norwegian Institute of Nature Research (NINA), who was the first author of the study. a new document refuting Burrows' hypothesis. "Not only has the immobilization of wildlife been periodically suspended in some countries immediately after, but the notion of extinction caused by a researcher persists in the scientific literature."

Jackson studied the wild dog in the great ecosystem of Serengeti-Mara for his doctorate. at the Norwegian University of Science and Technology (NTNU). He has worked with his colleagues at NINA, NTNU and the Tanzania Wildlife Research Institute (TAWIRI) to examine all of Burrows' arguments and re-evaluate them using an alternative approach.

These three research institutes are all part of AfricanBioServices, an EU-funded project that studies the effects of climate change, population growth and land use on biodiversity and communities. localities of the Greater Serengeti-Mara ecosystem, with the aim of designing new approaches. sustainable development.

Their article, published in the scientific journal Ecology and Evolution, shows that wild Serengeti dogs have not been victimized by well-meaning seekers, but have probably left the park for another reason: lions.

Missing, not extinguished

Although a number of other studies have attempted to demystify Burrows' argument, proponents of this hypothesis have discredited these studies because they had been conducted in other ecosystems and not in the Serengeti.

The Burrows hypothesis indicates that one of the main reasons for the disappearance of wild dogs is that their life situation in the park has put them in contact with rabies and canine distemper. So, how do you refute that, especially since wild dogs have disappeared from the park?

Jackson says it's easier than you think.

"Although much of the scientific literature has evoked the" disappearance of the population "in Serengeti National Park," the population has never gone extinct in the area, "Jackson said.

In fact, he said, the wild dog population has actually survived in the eastern part of the Greater Serengeti Mara ecosystem. This population has been studied and monitored since 2005. Some of these wild dogs even had a GPS collar, which showed that animals occasionally visited the park. This information is very important because it shows that wild dogs have access to the park. And if they had access to the park, they could have chosen to install it – at least in theory.

But they did not do it.

This gave the researchers an ideal opportunity to review all the arguments put forward by the Burrows promoters, to re-evaluate them and then to show why they are wrong.

A lot of rabies, canine distemper

Wild dogs living outside the National Park, in the Ngorongoro Conservation Area and in the Loliondo Game Play Area, are exposed to rabies and distemper at levels as high as even higher than those inside the park when they disappeared. new paper explains.

This means that the wild dogs that Jackson and his group examined had a similar exposure to the disease, or worse, than the wild dogs that Burrows and his colleagues say were exterminated by the researcher who manipulates them.

Thus, if the manipulation caused enough stress in wild dogs in these two regions to weaken their immune system and make them vulnerable to rabies or canine distemper, there was sufficient source of disease in the area to infect them. .

Radio collars and relocation stress

Currently, there are approximately 120 animals in the region in 10 packs, most of them in the Loliondo controlled area. TAWIRI researchers have been studying these animals since 2005, including using radio collars.

Between 2006 and 2016, 121 wild dogs in this region were immobilized and manipulated by researchers. Forty-five were stuck on the radio.

The Burrows group argued that wild dogs that had been handled by researchers "were significantly less likely to survive for 12 months after the date of first manipulation". Jackson and his colleagues looked at the ability of the 121 wild dogs outside the national park to survive a year after handling them.

When they looked at the numbers, 87.6% of the 121 dogs, or 106 animals, had survived at least 12 months after handling them. They also looked for figures on the transfer of 67 wild dogs from 6 packs to Serengeti National Park between 2012 and 2016.

As a general rule, when animals are transferred, they are monitored in pens for a period before release. In this case, dogs were held on average 313 days and 95.5% survived 12 months or more after being handled. In contrast, when the researchers examined another group of 54 wild dogs from the same area that had been immobilized but not captured or transferred, they found a lower survival rate of 77.8%.

"Therefore, long-term stressful interventions have not caused outbreaks, and the high survival rate does not support the Burrows hypothesis," the researchers wrote.

A lot of play and a lot of space

More than two decades after their disappearance, there are still no wild dogs in the plains of Serengeti National Park, although there is plenty of game and a lot of space. Why not?

Roel May (NINA), one of the co-authors of the study, thinks the answer to this question also explains why the park's population has disappeared in the first place – lions and hyenas.

"The movement behavior and use of the home range of wild dogs suggest that they face a trade-off between forage availability and landscape features that provide a refuge, which means that they can not be found anywhere." they are key determinants of wild dog occurrences in the Serengeti, "said May.

Wild dogs are predators, it is true, but they can also be bullied and killed by larger predators, such as lions and hyenas. In particular, lions and hyenas are effective at scare wild dogs so that they can eat them themselves, a phenomenon called kleptoparasitism.

The Serengeti is so rich and full of game for a reason. This is a high quality and mostly flat habitat, as lions and hyenas, as top predators, may prefer to live.

Lower level predators such as wild dogs move to lower quality habitat, such as the hilly terrain on the east side of the park. Researchers say that mountainous habitat also protects wild dogs when they are born and raised young.

"When the wild dog population of Serengeti was declining, the spotted hyena population in the park grew from 2200 to 5500, and the lion population grew in a similar way," Jackson said. "When hyenas scare wild dogs of their killings, they can not get enough calories to reproduce."

Researchers say the evidence is very clear: the growing competition from lions and hyenas, combined with an epidemic, is probably what struck the final blow to the Serengeti wild dog population in 1991, not to induced deaths by the researcher.

"Instead of local extinction, the disappearance of wild dogs in the Serengeti plains was more likely a contraction of their range in response to increased competition with these large carnivores," said May.

In addition, the use of radio collars and other tools to understand animals such as wild dogs is an important tool to help protect the species. Although some cases of animal mortality result from handling, the overall benefit to the species is positive, said Eivin Røskaft, NTNU biologist and coordinator of the AfricanBioServices project.

"Of course, there is a balance between disturbances and important knowledge about the conservation of large carnivores, especially in a world where all large carnivore populations are in rapid decline," Røskaft said.

"Although animal welfare and ethical considerations remain paramount, most information relating to the management and conservation of endangered species would be impossible to obtain in the absence of radio-telemetry and other techniques. requiring the intervention of researchers, "said Mr. Jackson.

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More information:
Craig R. Jackson et al., No evidence of handling mortality in the Serengeti African Wild Dog population. Ecology and Evolution (2018). DOI: 10.1002 / Ece3.4798