New World Vultures Essay, Research Paper

Compare and Contrast: New World Vultures vs. Old World Vultures

Old morphological classification grouped all diurnal raptors together, into one large order named the falconiformes. Within that were five broad families, of which were the New World vultures, the osprey, accipitrids (hawks, eagles, owls, and the Old World vultures), the falcons, and the secretary bird of Australia. With modern technology, and through a process known as DNA-DNA hybridization, taxonomists have been able to see that Old World vultures and New World vultures are completely unrelated. In fact, New World vultures have been found not to be related to any other raptors, they have been placed with the storks in the taxonomic order. Biologists have also noted many physical differences that American vultures share with storks. The vulture lacks the powerful hind toe (hallux) of other raptors and they have “perforate” nostrils, with a hole through the beak from side to side. Most American vultures also have an excellent sense of smell, which is lacking in other raptors and the Old World vultures alike.

The similarities in both classes of vultures are not due to being related, but to convergent evolution. Vultures on both sides of the Atlantic have bare heads because they feed on carrion. Feathered heads would become matted with blood from feeding inside large carcasses, while bare skin is much easier to keep clean. Since their prey doesn’t require killing, vultures lack specialized feet and talons. Some New World vultures cannot completely close the foot to grab. Unlike Old World vultures, American vultures have a well-developed sense of smell. Their sense of smell is even able to discriminate between meat that is merely spoiled and that which is completely putrefied. The Old World vultures probably haven’t evolved a sense of smell because most species live on open plains or in mountains, where carcasses are easily found by sight. Biologists have found these vultures to have up to eight times the amount of receptor cells in the eye than the human, while New World vultures may have only two to three times the amount. The New World vultures, just like their stork relatives, lack a syrinx and therefore can only hiss and grunt. All other vultures have the ability to produce a full call.

One unusual behavior observed in the American vultures not observed in others is the way they keep themselves cool. Sharing the behavior with their cousins, the storks, they will defecate on their bare legs, which keep them cool as the wind blows over the damp surface. For this reason, these birds are banded with wing tags rather than normal leg bands because the excreta builds up in a heavy, dangerous ring. Another behavior observed in Old World vultures but not in American vultures is the production of pellets. Other raptors will periodically regurgitate indigestible parts of prey such as bones and feathers. This has never been observed in American vultures.

All vultures are carrion specialists. Both the Old and New clans are extremely efficient at finding and using carcasses. Vultures have a much greater tolerance to pathogens than most animals. They are highly resistant to botulism, and hog cholera viruses. Thus, their feeding activities can help stem the spread of disease, especially in tropical climates. Although uncommon in most raptors, piracy of food is commonly seen amongst all vultures. In places where the food source is not as abundant as usual, this behavior becomes prominent.

The social structure in vulture families is unique. Many are social in their feeding and roosting habits. Unlike American vultures, Old World vultures are completely gregarious, roosting, feeding, and breeding in flocks. A clear dominance hierarchy is observed in flocks of feeding vultures. During the feeding process dominance shifts, one individual and then another asserts itself, only to lose preeminence to other, hungrier vultures.

Over time, these two groups of vultures have filled the same niche on different hemispheres of the globe. Evolution has made the two converge to share many similar features and many different ones. Each individual species has become specific to its habitat but they have all become alike at the same time.