The column Why do vultures circle dead stuff? (06-Jun-2001) made me remember another vulture-related question I’ve always wondered about. Namely, if you observe turkey vultures soaring, you’ll notice that they sort of “rock” side-to-side, as if they were unstable. In fact, this is an easy way to differentiate between vultures and hawks that are a long way off. Why do vultures do this? I assume that there is some real reason; i.e., the side-to-side motion allows the bird to smell the air easier. Anyone know?
I always thought they were simply riding the higher air currents, the warm air streams.
Might it have something to do with buzzards’[sup]*[/sup] longer wingspans?
[sub]* Yes, I know that they’re also called turkey vultures, but I’m from Northeast Ohio. They’re buzzards, demmit, regardless of what everyone else calls them.[/sub]
I’m certain that red-tailed hawks, which are somewhat smaller than turkey vultures, do not exhibit this kind of “unstable” flying behavior. As far as I know (i.e., on the occasions that I’ve seen them), bald eagles, which are somewhat larger than vultures, don’t waggle their wings, either. Again, as far as I know, all three types of birds ridfe thermals in the same way.
I seem to recall, although I could be mistaken, that vultures (turkey vultures only?) are the only North American birds that exhibit this behavior, thus making this a reliable way to positively identify a vulture. My guidebook semi-supports ths by noting that a turkey vulture “rolls and sways from side to side” while soaring. No such note for other birds.
Card-carrying birdwatcher checking in here.
Yes, you can use this to tell the difference in the air between a turkey vulture and a black vulture. Turkey vultures have a V-shaped wingspan and tilt back and forth. Black vultures have a level wingspan and don’t tilt.
Dunno why this should be, but the most plausible explanation, to my mind, is that female turkey vultures think it looks kewl. Like the “bowerbird female choice” thing.
It’s also possible it allows them to drop out of the thermal and get down to where the food is, quicker.
Also want to point out that New World vultures are considered to have evolved from storks, and are not very closely related to raptors (hawks).
I’ve heard that operators of natural gas pipelines add a rotting-meat odor to their product. If they see vultues circling over some lonely spot, the operators know to check the pipe for leaks.
It’s an interesting idea, but the odor added to natural gas is actually based on skunk spray, and the purpose is to warn any humans who might be in the presence of a leak. The methane itself is odorless, so nobody would know to evacuate.
I don’t think they’d bother, with the transport pipelines: Out in the open, there’s very little fire hazard, and if enough is leaking out to cut into profits, they’d probably be able to pinpoint it by measurements of pressure and flow. Besides, there’s plenty of genuine rotten meat to attract vultures, so they’d have a lot of false positives to check.
My SWAG is that the “unstable” flight of the Turkey Vulture is a direct result of their ability to make use of even small areas of rising air for lift. There are two ways a soaring (non-flapping) bird can obtain lift: from thermal bubbles of warm air rising from a surface heated by the sun; and by updrafts produced when moving air is deflected by a barrier such as a mountain ridge (or on a smaller scale even by a tree or a rock). Turkey Vultures have a relatively low wing loading (ratio of body weight to wing area) and hence can exploit small or weak thermals or tiny updrafts. I suspect that they wobble as they move between these unstable and variable areas of lift. Here in Panama TVs typically fly only a few meters above the forest canopy, using the miniscule updrafts produced by variations in canopy height. On migration, however, TVs make use of strong thermals or updrafts off ridges, and their flight is then steady and level. (Nearly the entire North American population migrates through Panama on its way to South America, most of them passing right over Panama City, along with Swainson’s and Broad-winged Hawks. A couple of years ago we did a count and registered 1.5 million raptors in six weeks - the biggest one-day count being 400,000.)
The Black Vulture, on the other hand, has a higher wing loading and usually must flap every few seconds to stay aloft, unless there are very strong thermals. I suspect that most hawks and other raptors also only soar when thermals or updrafts are strong and hence show more stable flight than TVs.
No, a few others do this as well (although TVs are the only large birds that do so). The Northern Harrier (formerly known as the Marsh Hawk) also has a low wing loading and flies with its wings in a dihedral, and also shifts from side to side as it quarters low over grassland or marsh. And the Zone-tailed Hawk of the American southwest (and Central and South America) is thought to mimic the Turkey Vulture in order to lull its prey into a false sense of security - although it is much smaller, it has a very similar flight style, profile, and coloration (except for its banded tail). It can easily be mistaken for a TV in flight at a distance.
I doubt this one, as females fly exactly the same way as males.
I was going to mention this in the column, but it was getting a bit long. The most obvious feature in which they differ from true raptors are the feet, which are non-grasping and have relatively blunt claws, much like those of storks. Several storks, notably the Marabou of Africa and the Adjutant of Asia, are vulture-like carrion-eaters.
As Chronos stated, the compound, ethyl mercaptan, is added to odorless methane for safety so that leaks can be detected. However, the chemical is also emitted by rotting meat and attracts vultures. This has sometimes fortuitously been used to find pipeline leaks. From this site:
Ever been to the Hinkley, Ohio, Buzzard Festival?
George
Straight Dope Science Advisory Board (Curator of Birds)
Hasn’t everyone?
Not I.
-sigh- 
It’s one of my fondest dreams.
Hello folks.
In my humble opinion, my only credential being a modest interest in aviation, turkey
vultures fly in circles simply to take advantage of thermal and/or slope lift. If there is food
to be had, the turkey vultures would be on top of it. But to search for food with minimum
effort, and to gain the altitude necessary for a good search, the “buzzard” will circle in the
“sweet spots” of rising air to gain altitude, then fly off to search for food when their
altitude permits the potential energy to reach their destination. We call it “coring a
thermal” in glider speak.
I’ve had experience flying RC gliders among buzzards in thermal and slope lift. As long as
I keep the sailplane below them, they are not threatened, and will accept the company. As
well as they fly, it is near impossible to get above them anyway… They are true masters of
the air.
I’ve never witnessed turkey vultures circling above a food source, although I’ve been told
all my life that it is why they circle, my observations of the fascinating creatures have
proven otherwise to myself.
Once again, just my humble opinion, any arguments are welcome!
Welcome to the Boards, sparky!
You are correct in that most of the time, when you see vultures circling, they are just using thermals to gain altitude before they glide off to search for food or to travel. (However, in my experience vultures sometimes seem to circle just to “hang out” even when they are not hungry. They are such efficient soarers that it may not cost them much in energy versus perching, and in the meantime they can check out the other vultures in the neighborhood, or perhaps keep an eye on things just in case something interesting turns up. Or maybe they just enjoy basking in the sun while soaring.)
They definitely do sometimes circle over a food source, as a visit to Panama City’s garbage dump or fish market would amply demonstrate to you. If they locate a carcass out in the open, they will often make a few passes over it to check it out; if there is already a crowd of vultures around they may circle a bit, probably in order to assess their chance of getting a share before they settle. And if the carcass is hidden below the forest canopy, Turkey Vultures may need to make several passes or circle around for a while in order to zero in on the source of the odor. They don’t want to descend below the forest canopy until they have the location pinpointed.
In any case, the question was, “Why do buzzard circle above dead stuff?,” not, “Why do they circle in general?”