By Robert Mulvihill / National Aviary ornithologist
This is one of a series presented by the National Aviary, America’s bird zoo. The National Aviary works to inspire a respect for nature through an appreciation of birds.
When they’re afoot, vultures may appear ungainly — even ugly — but they are the epitome of grace and beauty when they are on the wing. Their aerial mastery is an essential adaptation because vultures often must travel hundreds of miles and many days in search of an animal carcass on which to feed. The uncertainty of their food supply in both time and space has selected for energy-saving flight morphology and behavior. The broad slotted wing tips of vultures provide exceptional lift, even at the slow flight speeds needed for turning tight circles within rising air thermals. Consequently, vultures can soar for several hours over many square miles in search of their next meal.
A vulture circling over a potential meal often attracts the attention of other keen-eyed vultures. So, when a carcass is discovered, it can turn into a gluttonous free-for-all as vultures fall all over one another to grab pieces of anything edible. At a single feeding, a vulture can easily down more than two pounds of meat, animal hide and bones, the added weight of which can render it temporarily flightless. Fortunately, all vultures have extremely potent digestive juices, so not only is the food that they eat digested quickly, but also potentially harmful bacteria in the meat are killed in the process. In this way, vultures help curb the spread of disease on every continent where one of the 15 species of Old World vultures and seven species of New World vultures lives.
Presently, scientists believe that New World and Old World vultures probably are not closely related, despite the fact that they look and act alike. They instead think that the two groups have a different ancestry and that their many similarities are a product of what is called “convergent evolution.” In the same way that you can build a plane that will fly out of wood or metal or plastic, nature can build a large avian scavenger out of different genomes. So, New World and Old World vultures share several traits — sparsely feathered heads, hooked beaks, large, broad wings and keen eyesight — not because they are closely related, but because they evolved through natural selection into a similar niche, or ecological role. It is a good thing for humans that they did, because the vital role that all 22 species of vultures fulfill by consuming dead animals helps to preserve the health of our environment. And that makes it a very bad thing that half of the world’s vulture species are threatened or endangered with extinction.
Two New World and one Old World vulture species call the National Aviary home: our black vulture and Andean condors are New World vultures; the hooded vultures that appear in many of our free-flight shows are an Old World species. You can come and see all three species during a fun “Vulture Weekend at the National Aviary” on Saturday and Sunday.
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