Although India managed to counter a steep decline in its vulture population in mid - 1990s, these efficient scavengers are in danger of disappearing in many parts of the world primarily due to the presence of toxins in the carrion they consume.
Poisoning is the greatest extinction risk facing vultures, and impacts 88 percent of threatened vulture species, the study said.
Now, the center of the vulture crisis is in sub - Saharan Africa, the researchers noted.
In the mid - 1990s India experienced a precipitous vulture decline, with more than 95 percent of vultures disappearing by the early 2000s.
"That was a massive collapse that led a lot of people to really focus more attention on vultures, " said one of the researchers Evan Buechley from University of Utah in the US.
The cause was eventually traced to diclofenac, a veterinary anti - inflammatory drug that relieved pain in cattle, but proved highly toxic to vultures.
Hundreds of vultures would flock to each cattle carcass.
And if the cow had recently been treated with diclofenac, hundreds of vultures would die.
Because of this highly gregarious feeding behaviour, less than one percent of cattle carcasses contaminated with diclofenac could account for the steep vulture decline.
Fortunately, international cooperation led to a total ban on veterinary diclofenac use.
The numbers of vultures have stabilised, and are now showing signs of slowly increasing, Buechley said.
Losses of vultures can allow other scavengers to flourish, Buechley pointed out in a report published in the journa Biological Conservation.
For example, following the decline of vultures, India experienced a strong uptick in feral dogs - - by an estimated seven million.
The increase in dogs, potentially feeding on disease - ridden carcasses, is thought to have at least partially caused the rabies outbreak that was estimated to have killed 48, 000 people from 1992 - 2006 in India - - deaths that may have been avoided if not for the disappearance of vultures.
Members of the Parsi sect of Zoroastrianism experienced a different impact.
For thousands of years, the Parsi people have placed their dead on exposed mountaintops or tall towers for vultures to consume.
The practice is called "sky burial. "
But with few vultures and unable to properly handle their dead, the Parsis experienced a crisis within the faith.
Some constructed captive vulture aviaries.
Others talked about desiccating bodies using focused solar mirrors.
The Parsis' plight exemplifies the vultures' role in south Asian society - - and the various impacts if the vultures are not there.
Although the vulture crisis in Africa is ongoing, the researchers can predict what the outcome will be, based on previous experiences in India.
Crows, gulls, rats and dogs will boom.
And the rabies outbreak in India may just be a prologue, because several sub - Saharan Africa countries already have the highest per - capita rabies infection rates in the world, the researchers noted.
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