Old World vultures are not closely related to the superficially similar New World vultures and condors, and do not share that group's good sense of smell. The similarities between the two groups of vultures are due to convergent evolution rather than a close relationship. They were widespread in both the Old World and North America, during the Neogene. Old World vultures are probably a polyphyletic group within Accipitridae, with Palm-nut Vulture, Egyptian Vulture and Lammergeier separate from the others.
Both Old World and New World vultures are scavenging birds, feeding mostly from carcasses of dead animals. Old World vultures find carcasses exclusively by sight. A particular characteristic of many vultures is a bald head, devoid of feathers. If vultures had head feathers, they would become spattered with blood and other fluids when the vultures ate flesh from carcasses, and thus would be difficult to keep clean.
Some species of vulture are very susceptible to diclofenac poisoning, which causes the birds to suffer from renal failure and death, and this had caused a very marked decrease in wild vulture populations in the Asian subcontinent, where diclofenac used for farm animals has directly led to poisoning of vultures. Often farm animal carcases containing diclofenac in their flesh are left out in to open for vultures to eat and tidy up. Meloxicam has been found to be harmless to vultures and should prove an acceptable alternative to diclofenac.