Vultures fill a critical niche in India as scavengers, so when they began dying out due to an unknown toxin, wild dogs filled that role in their urban food web. Vultures feed on the carcasses of cattle which, in India, are left in carrion dumps and not eaten. After a medical agent used in cattle was found to be poisoning the vulture population, wild dogs and rats quickly filled the niche the birds vacated; however these new scavengers meant big trouble for the human population of India.