I heard a story from a reliable source, who in turn heard it from a fairly reliable source. So believe it or not:
One day a resident of a Nairobi, Kenya — a fairly well off person who liked to collect things — called the police to report that his leopard had gotten out.
So, the police called around and got some leopard traps. Not hard in a place like Nairobi.
They put a dozen, maybe two dozen, traps around the area, in town.
That night and the next, they caught a half dozen or so leopards. None of them were the missing animal. All the caught leopards were wild.
(How can you tell a wild vs. a tame leopard caught in a leopard trap? Do you really have to ask that question.?)
Meanwhile, there are the dogs. Dogs that are feral in that region of Africa, in any of the savanna regions of Kenya, Tanzania, and Uganda, or for that matter the Eastern Congo, have a high probability of having rabies. Most of my personal encounters with rabies were in that region (not counting the Great Rabid Raccoon Rage of New England a few years back, an interesting story of its own).
In India, there is exactly the same problem. Lots of feral dogs, rabies abound, but there are also a lot of leopards.
But leopards find feral dogs easy prey.
A study has found the world’s densest population of leopards may be saving human lives by feeding on feral dogs.
The international study, led by University of Queensland researchers, shows that leopards may reduce bites and subsequent rabies risk for people by consuming feral dogs in Mumbai, India.
School of Earth and Environmental Sciences PhD students and authors Christopher O’Bryan and Alexander Braczkowski found that a small population of 35 leopards in Mumbai may consume about 1500 dogs per year, preventing around 1000 bite incidents, and 90 potential rabies cases.
“Stray dogs are the leading cause of rabies deaths in India, killing 20,000 people per year, so if there’s a natural predator in the landscape that can reduce that risk, it’s worth investigating,” Mr Braczkowski said.
The researchers compiled previous studies and found the average leopard diet in Mumbai contained 40 per cent stray dog.
“These results highlight the need for more research on the impacts of predators on harmful pest species, such as feral dogs,” Mr Braczkowski said.
“Leopards are frequently persecuted throughout the region with conflict often arising over livestock, but we show these unique predators can also be beneficial to human societies,” Mr O’Bryan said.
“Our paper discusses the role of leopards at reducing the density of stray dogs around the Sanjay Gandhi National Park in Mumbai, a protected area located in the middle of the sixth most populated city in the world.”
The researchers stress the importance of evaluating both the negatives and the positives of large carnivores in human-dominated areas.
“While it’s very important that we evaluate the benefits of these leopards and similar large carnivores, it’s equally important to assess the costs of these species to local communities, such as attacks on people,” Mr O’Bryan said.
“The real challenge is navigating the costs with the benefits, and identifying those cases of net-benefit.”
Leopards have lost nearly 80 per cent of their global historic distribution, and are under threat from conflict with people, competition for prey, and habitat loss, according to the International Union for the Conservation of Nature.
Research fellow for the Global Change Institute Dr Hawthorne Beyer was also a senior author of the article.
The article Leopards provide public health benefits in Mumbai, India appears in the March 2018 edition of Frontiers in Ecology and the Environment journal (DOI: 10.1002/fee.1776).