STOP! Why you should start loving and valuing VULTURES, HYENAS and other scavengers
Vultures are highly adept at cleaning up carcasses, making them the most efficient scavengers in the animal wo
Vultures and hyenas play a vital role in preserving ecosystems and preventing diseases such as rabies. Should we value them more?
Scavengers are vilified and often feared. Around the world, creatures including vultures, hyenas and beetles that feed on animals that are already dead are considered unpleasant, dirty and dangerous.
In his novel The Green Hills of Africa, Ernest Hemingway described the hyena as a “devourer of the dead, trailer of calving cows, ham-stringer, potential biter-off of your face at night while you slept, sad yowler…”. And since ancient times, vultures have been viewed as harbingers of death and symbols of bad luck.
But the more scientists find out more about these consumers of the dead, the clearer it becomes that we should be valuing and protecting scavengers far more than we do today. They play a vital role in preserving the ecosystems they inhabit and provide important health and economic benefits. By devouring carcasses, they prevent pathogens from spreading to humans and wildlife and contaminants from leaching into the environment.
New studies are revealing the enormous health, environmental and economic benefits that vultures, hyenas and other scavengers provide and highlighting the costs associated with losing these vital creatures.
Vultures are highly adept at cleaning up carcasses, making them the most efficient scavengers in the animal world, says Vibhu Prakash, principal scientist at the Bombay Natural History Society who oversees its vulture conservation breeding programme. “They can eat almost 40% of their body weight in bulk, whereas other animals can only eat about 5%,” he says.
But these scavenging birds are disappearing at an alarming rate in South Asia and Africa.
The decline of India’s vulture populations began in the 1990s and happened very quickly. In the early 1990s, there were between 100 and 160 million vultures in the country.
“They were absolutely everywhere in India,” says Bowden. “They were doing an amazing job of cleaning up carcasses on a huge scale.”
But by the turn of the century, tens of millions of the birds were mysteriously dying. The populations of India’s three most common vulture species together fell by more than 97% between 1992 and 2007.
The vultures were tested for heavy metals, pesticides and other pollutants but no single cause of death could be identified. Eventually, autopsies revealed that many of the dead vultures had suffered from a type of gout caused by kidney failure. Researchers realised that vultures were being poisoned by the painkiller diclofenac – widely used as a veterinary drug to treat cattle – when they were feeding on livestock carcasses.
“There’s something unusual about vultures’ metabolism…they can’t [process] diclofenac and that causes kidney failure,” says Bowden.
India’s feral dogs soon benefitted from the vultures’ decline, he says. Due to the fall in vulture populations, cow carcasses piled up and the number of feral dogs surged as they became the main scavengers.
This had a knock-on effect on human health as it led to a rise in rabies deaths, says Prakash. “There has been an increase in rabies in India over the past 20 years,” he says.
According to a study by scientists at the University of Bath, the vulture decline made way for at least 5.5 million extra feral dogs in India, responsible for an additional 38.5 million bites between 1992 and 2006.
Using a national survey which showed that 123 out 100,000 people who are bitten by dogs die of rabies, the scientists calculated that at least 47,395 people died as a result of feral dogs becoming the dominant scavengers in India.
“Vultures provide a number of benefits to Indian society, from waste disposal to spiritual values,” says Tim Taylor, an author of the study and a senior lecturer in environmental and public health economics at the University of Exeter. “Waste disposal is particularly important, as they can reduce the food available for stray dogs and hence help to keep dog populations in check.”
Taking account of the average cost of treating rabies patients and dealing with the additional deaths, Taylor and his colleagues concluded that the vulture decline caused by diclofenac indirectly cost India $34bn (£28bn) between 1993 and 2006, equivalent to 3.6% of the country’s GDP in 2006.
“It is important that vultures be restored, as they are a valuable resource for India and hold an important place in the ecosystem,” says Taylor.
In Africa, vultures are also dying rapidly, but for different reasons.
Across the continent, vulture populations have shrunk by up to 97%. Seven out of the 11 African-Eurasian vulture species are at risk of extinction.
Here, vultures are the unintentional victims of poisoning aimed at killing large predators, such as lions, says Darcy Ogada, Africa director of the Peregrine Fund, a non-profit that protects threatened and endangered birds worldwide.
Farmers who lose cows to a pride of lions spread highly toxic pesticides on the carcasses in the hope of killing the predators, but often the lions never return and the vultures are the ones that suffer, she says.
Poachers also sprinkle pesticides on dead elephants to kill vultures and stop them from alerting park rangers by circling overhead, she adds.
Many vultures are also killed because of religious beliefs. Vulture heads are used for traditional medicine and in “black magic”, especially in southern Africa, says Ogada.
Vultures’ decline in Africa has also created a health risk, according to Ogada’s research. In a 2012 study carried out in Kenya, Ogada and her colleagues found that more scavenging mammals gathered around carcasses when vultures were not present, especially hyenas and jackals.
“When there are no vultures, there are a zillion other things on the landscape that want to eat the carcass,” says Ogada. “But none have the ability to clean the bones the way the vultures do, so that there’s not even a fly on it.”
A decaying carcass which isn’t cleared acts as a “hub for disease transmission”, where infected animals gather and spread pathogens, says Ogada. “There were three times as many [moments of] contact [between different animals] at carcasses that didn’t have vultures.”
Hyenas and jackals are also far more likely to come into contact with humans than vultures and act as a vector for disease.
While the health benefits of vultures often remains underappreciated, it’s perhaps even less well known that vultures’ unpleasant (to us) habits also may have benefits for the climate. In fact there may be serious environmental risks associated with the decline of vultures worldwide.
In India, the feral dogs can’t match the efficiency and speed of vultures when it comes to disposing of carcasses, says Bowden. This means that many carcasses are left to decompose naturally or, in some cases, are incinerated.
Carcasses release greenhouse gasses when they decompose, including CO2 and methane. But most of these emissions are prevented if the vultures dispose of them, according to a study released earlier this year by scientists at the National University of Comahue in Argentina.
The study estimated that a single vulture consumes between 0.2 and 1kg (7 and 35oz) of decaying carcass meat per day, depending on the species. When it’s left to decompose naturally, each kilogram of carcass meat emits about 0.86kg of CO2 equivalent, or CO2e. Using these estimates, the scientists calculated that the 134-140 million vultures worldwide could be preventing tens of millions of tonnes of emissions per year, an amount comparable to the emissions of some countries.
“This ecosystem service contributed by vultures to humans and nature cannot easily be replaced by other species, including humans,” the study notes.
However, due to the absence of vultures, rotting carcasses in India are now often buried, dumped at landfill sites, or thrown in the river, where they risk contaminating the water and result in odour pollution around cities, says Prakash.
In 2004, after scientists discovered that diclofenac was responsible for vultures’ rapid decline, they launched breeding programmes to help boost populations across India, with the first captive-bred birds released in 2021. But it’s slow progress – vultures mature when they are about five and release only one egg a year, says Prakash, and just half of the birds reach adulthood.
Bombay Natural History Society plans to release about 20-30 birds each year through the programme. But the survival of these birds depends on ending the use of diclofenac, says Prakash. India banned the drug for veterinary use in 2008 but a recent study found that it was still widely available and continued to pose a high risk to vultures.
Scientists are working to create vulture safe zones, where they are monitoring the availability of diclofenac and carrying out population surveys.
Vultures aren’t alone among scavengers in being often unfairly maligned despite the huge benefits they provide humans – hyenas also provide valuable ecosystem services. The shrieking pack hunters play a vital role in protecting humans and animals from diseases, such as anthrax and tuberculosis.
Due to the fall in India’s vulture populations, cow carcasses piled up and the number of feral dogs surged
A 2021 study by the University of Michigan in the US found that scavenging hyenas provide significant health and economic benefits to the African cities they roam. Spotted hyenas collectively remove 207 tonnes (456,000lb) of animal carcass waste annually in Mekelle, the capital of northern Ethiopia’s Tigray region, the researchers calculated. The hyenas feed on livestock carcasses dumped in landfill sites on the outskirts of Mekelle. The researchers wanted to understand whether by devouring these carcasses, hyenas helped prevent pathogens from spreading to people and livestock.
They compared the public health and economic outcomes of times when hyenas were present to when they were absent, and found that their scavenging annually prevented five infections of anthrax and bovine tuberculosis (TB) in Mekelle’s residents and 140 infections in cattle, sheep and goats.
“We found that hyenas are contributing to the management of disease and controlling the spread as well,” says Chinmay Sonawane, lead author of the study who is currently completing a PhD in biology at Stanford University in California.
Anthrax and bovine TB are responsible for about 6,000 human deaths and 500,000 cattle deaths annually in Ethiopia, the study authors note.
“These are just two diseases out of dozens, if not hundreds, that might be out there,” says Sonawane. “The sanitation services provided by hyenas might also be preventing the transfer of novel diseases to people.”
The hyenas’ scavenging also saved Mekelle $52,000 (£44,000) annually in health treatment costs and livestock losses avoided, the study found.
“There are really big economic benefits for the local community,” says Sonawane. People living in villages around Mekelle therefore “reap the benefits” of having hyenas around, he says.
Communities on the fringes of Ethiopian cities “have coexisted with hyenas for as long as they’ve both been present, and certainly understand the sanitation services they provide”, says Sonawane. “But that additional step of disease control might not be as tangible for them.”
Despite the services they provide, vultures and hyenas aren’t valued worldwide, scientists say.
“Hyenas are regarded as Africa’s most successful predator…So that also causes a lot of conflict and maybe adds to the [negative] narrative,” says Sonawane. “Films like the Lion King probably don’t help,” he adds.
“Vultures are associated with death and there are superstitions and beliefs about them in lots of countries,” says Bowden. “In Nepal, if a vulture sits on your house, it is considered bad luck and means someone is going to die. We are battling to highlight the important and positive role that vultures play.”
By raising awareness of scavengers’ ability to eliminate harmful toxins from the environment and prevent the spread of dangerous diseases in humans, however, conservationists hope to boost the recovery of these critical species. In doing so, perhaps they can help humans end our vilification of scavengers once and for all, and instead value them for the many benefits they provide us.