By Rajasvi Gandhi
In the 1990s, India experienced a crisis where the vulture population dropped by about 95%. This was the fastest decline of any avian species in history. Within a few years, there was a sharp increase in the population of feral dogs that temporarily replaced vultures as scavengers in the ecosystem. A massive outbreak of rabies soon occurred, mainly caused by the dogs feeding on diseased carcases, and killed 48,000 people between 1992-2006. Such a tragedy could have been avoided had the vulture population survived. Vultures easily manage to avoid being affected by most toxins. At the same time, scavengers such as dogs become carriers of these diseases, circulating them across species.
Why do we need scavengers?
Scavengers are organisms that consume dead and decaying animal and plant matter. Instead of hunting other animals like most carnivores, they eat animals that either die of natural causes, or are killed by other animals. Hence, they perform an extremely important function in the food web—that of keeping the ecosystem free of carrion. They also prevent contamination of water by keeping disease-causing microorganisms in check.
The organism does not need to be dead to be a food source for scavengers. In the case of rats and blowflies, scavengers consume the flesh around the wound, leaving the animal relatively healthy. By breaking down the compounds present in matter, they ensure the recycling of nutrients in the environment. This is a vital and delicate ecological balance that is essential for the survival of the world.
What makes vultures indispensable?
Vultures have biologically evolved to excel at scavenging. This allows them to keep the disease-causing microorganisms in check, preserve the balance of nutrients, the number of species and water bodies in an ecosystem. Their many adaptations include a strong digestive system unaffected by many common diseases (like rabies, bubonic plague, anthrax). The extremely low pH of their digestive enzymes dissolves a majority of the microorganisms found in their meals. Most vultures also have a keen sense of smell (such as the turkey vulture), sight and aggression (such as the black vulture) that allows them to locate a rotting carcass from thousands of feet away.
Many vultures have little to no feathers on their heads. This keeps them free of contamination and allows the elements to wash away the remaining toxins. They possess weak talons as opposed to predators like raptors, which provide them with better balance. They have a sharp beak for tearing into the flesh and bones of carrion. In order to cleanse their talons of germs, they simply urinate on them to dissolve the putrid remains. They have no possibility of carrying pathogens like various other scavengers due to their biological adaptations. Therefore, the reduction of vultures from an ecosystem that depends on them for the disposal of carrion disrupts its equilibrium.
Vultures under threat
The population of vultures faces threat all over the world, especially in Africa, Asia, and the United States of America. There are about 23 species of vultures—classified into Old World and New World vultures, out of which 14 are under threat, and nine are critically endangered. Threats to vultures include lead poisoning from consuming animals with gunshot wounds, electrocution, pesticide usage, and poisoning due to animal medication.
Revisiting the Indian vulture crisis, we find that the sudden drop in vulture population was attributed to kidney failure. This was caused by the liberal usage of Diclofenac as a painkiller for domestic livestock—a major food source for vultures. This drug accumulated in the bodies of cattle and contributed to the decline of India’s vultures, which lack a certain enzyme that prevents them from digesting Diclofenac. Although the drug was banned in 2006, its usage continues.
Is the damage irreparable?
Unfortunately, all efforts to sustain the vulture population in India are now considered unprofitable. Breeding vultures in captivity is a painstaking process since vultures take up to five years to mature and have a slow rate of reproduction. The arbitrary presence of Diclofenac in their food also prevents their self-sustained survival, leading to vultures being declared functionally extinct. The extinction of such an important species of scavengers has forced us to re-examine the crucial process of waste disposal carried out by vultures in the environment. The highly specialised diets and slow mating cycles of vultures make it less likely for other emergent species to replace their position in the food web.
According to recent research conducted by the International Union for Conservation of Nature and Natural Resources, scavenging birds are crucial for leading other scavengers to carcasses and limiting the spread of disease. As a result, the rapid decline of vulture populations coupled with highly virulent diseases and high population density can increase the occurrence of anthrax, bubonic plague, and rabies. Often, the importance of such a species is realised only after their loss. Investment in their conservation and study will surely have positive impacts on the environment, but only if carried out in a timely manner.
Featured Image Credits: Visual Hunt
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