We Should Embrace Scavengers and Predators
They’re being lost at an unprecedented rate, and that’s not good for human health and well-being
By Christopher O’Bryan and James Watson
March 13, 2018
[Note: This story is reprinted with permission of Scientific American.]
When we hear of vultures or dingoes or big cats such as lions, leopards and tigers, our first instinct may be to recoil. Like the grim reaper, vultures circle overhead when death draws near. In 1980 a dingo famously made off with the infant child of an Australian couple on a camping trip. And from a young age we develop an awe of our big cats in the wilds of Africa, India and the Amazon. For those who manage to get an up-close view, it’s an awe inseparable from fear.
So perhaps it will come as a surprise that many scavengers and predators are increasingly vulnerable today. That’s bad news for us all.
Let us explain: Many of these animals are being lost at an unprecedented rate, with more than three quarters of vulture species in decline; leopards disappearing across 78 percent of their historic range; and African lions predicted to decline by half in the next two decades. If these losses continue, the consequences could be catastrophic, based on what we know about the role these animals play in nature.
Even as predators and scavengers face new and growing threats, we are only just beginning to understand their value to human well-being — from disease regulation and agricultural productivity to waste disposal. In a paper published in Nature Ecology & Evolution we surveyed multiple studies demonstrating that such services are being provided by species ranging from mountain lions and bats to vultures and jackals.
Animals host over 60 percent of known human diseases, and predators and scavengers help prevent their spread by consuming the animal hosts of these ailments. For example, we found that by reducing the density of stray dogs in suburban Mumbai, leopards in turn reduce the human exposure to rabies, a virus that kills thousands every year.
We also found studies that point to foxes reducing Lyme disease risk by consuming rodents that host the pathogen. Insect-eating frogs may play a global role in reducing dengue fever by preying on mosquito eggs. Similarly, vultures and other scavengers may substantially reduce disease spread by rapidly consuming carcasses that would otherwise benefit stray dogs, rodents and other disease carriers.
In agricultural lands predators can reduce the need for pest control. We found studies that pointed to bats reducing corn crop pests by nearly two thirds, meaning a savings of over a billion dollars globally in pest control. Coffee plantations in Sulawesi, Indonesia, have significantly more crop output as long as birds and bats are eating pest insects. This has huge implications in nations where corn and coffee crops are substantial contributors to the economy.
We found in Australia dingoes benefit cattle farmers by reducing the number of kangaroos competing with cattle on grazing land. Likewise, falcons help the winery industry by preying on small bird species that feed on grapes, and frogs in Nepal increase the health of rice crops by feeding on problematic insects.
Scavengers play a particularly useful role by feeding on nonliving animals and other organic matter. Golden jackals have been shown to reduce an astounding 13,000 tons annually of domestic animal waste across Europe that would otherwise be both expensive to remove and present a great health risk.
Vultures in Spain can save the livestock industry $50 million a year by consuming carcasses that would otherwise need to be transported to processing facilities. Farther east in Yemen vultures in the rural villages on the islands of Socotra dispose more than 22 percent of organic waste. There is no reason to believe similar services are not being provided elsewhere across the globe.
In addition to these direct and indirect benefits provided by current predator and scavenger populations, conservation initiatives could provide additional benefits. For example, research suggests that if mountain lions were recolonized to the eastern U.S. over the next three decades, they would consume enough deer to reduce deer–vehicle collisions by 22 percent every year in the process saving 150 lives and 21,000 injuries while offsetting more than $2 billion in damage
Even though there are many tangible services documented from predator and scavenger populations, we understand the costs as well. Large carnivores in developing nations are a source of conflict, and many species pose real or perceived threats to humans. Nevertheless, many of these species are in a desperate state of decline due to their poor reputation, habitat loss and a changing climate.
It is time the conservation conversation moves from merely evaluating the societal costs of predators and scavengers to a serious discussion of the critically important services these animals can provide to humans in areas we occupy together. Only then may we acknowledge that although we may rightly or wrongly fear the vulture, the dingo or the leopard, there’s no question we need them.
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Christopher O’Bryan is a PhD student in the School of Earth and Environmental Sciences at The University of Queensland, Australia. James Watson is a professor in the in the School of Earth and Environmental Sciences at The University of Queensland, Australia, and director of the Science and Research Initiative at the Wildlife Conservation Society.