The most important factor contributing to the loss vulture population in India is

The answer is C, the administering of pain killers to cattle. The culprit is diclofenac, an NSAID given to cattle for inflammation and fever. Vultures that feed on carcasses of treated cattle absorb the drug, which causes visceral gout and kidney failure. Within a few years in the 1990s, three Gyps species (white-backed, long-billed and slender-billed) fell by over 95 percent.

Why the others are wrong:

• A and B: Viral and bacterial infections were studied as possible causes, but no single infection was shown to explain the collapse across regions. The drug link was established through post-mortem and field studies.
• D: Estrogen injections are not the documented cause. Oestrogen-type drugs are not linked to vulture mortality in this literature.

The concept is pharmacovigilance and the ecological effects of veterinary drugs. The Government banned veterinary use of diclofenac in 2006, and the Vulture Action Plan followed. This is a useful Mains point on One Health and regulation.

Trap: Aspirants pick infection options because vultures are often linked to disease. The question asks for the most important factor, and that is the veterinary drug.