Condors and vultures: their postures, their 'bald heads' and their sheer ecological importance

For no particular reason, here are some interesting raptor photos. Birds of many kinds often sit around with their wings only partially folded, partly hanging down at their sides; one reason for this is that they're sun-bathing and are using their wings to soak up heat. Among raptors, this behaviour is well known for Turkey vultures Cathartes aura in particular. But many others do it, and here's another New World vulture (cathartid), an Andean condor Vultur gryphus, doing the same thing [photo by Markus Bühler, taken at Berlin Zoo].


During cold weather, captive Andean condors are reported to mostly sit still, with their neck ruffs pulled up to the head. They expose the bare neck and naked breast patch in warmer weather. Occasionally, males kept with females will inflate their necks, at the same time changing the skin colour from pinkish-grey to "a distinct pale rose and sulfur yellow" (Gailey & Bolwig 1973, p. 60).

The condor's pose shown above reminds me of the pose adopted by this Lappet-faced vulture Torgos tracheliotos, photographed in captivity (I think in London Zoo) many decades ago.


I've used this photo before (in my review of Kaiser's The Inner Bird) because - one might argue - the pose helps remind people that a bird's wing is merely a tightly folded version of the maniraptoran arm. Anyway, I've always wondered why this bird was holding its wings like this: sun-bathing doesn't look likely on this occasion. Was the bird merely photographed in the act of folding its wings up, or was there something wrong with it? Torgos is an Old World vulture (an aegypiine accipitrid), apparently closely related to the Black or Cinereous vulture Aegypius monachus and the White-headed vulture Trigonoceps occipitalis (Lerner & Mindell 2005). The large size (wingspan up to 2.7 m) and robust bill of Torgos mean that it is dominant to other Afro-Arabian vultures at kills.

And while on the subject of aegypiine vultures...


This is the head of a griffon vulture (griffons: the eight or so Gyps species): I assume (based on the pale bill, straw-coloured iris and pale head and neck) that it's a G. fulvus (typically just called the Griffon vulture) [photo by Markus Bühler, taken at Berlin Zoo]. It serves to remind us well that most Old World vultures aren't 'naked headed' at all: they actually have a very respectable covering of fine, filamentous feathers. In fact, Torgos is the peculiar one in being naked-skinned. Rather than being anything to do with keeping clean at carcasses (the most usually proposed function for naked-skinned heads and necks), the peculiar head and neck feathering of griffons might be more to do with thermoregulation: these birds have to cope with rapid temperature fluctuations of as much as 70° C (Ward et al. 2008) as they move rapidly from soaring in cold, high-altitude air to running around on the hot ground in tropical environments. I've had some nice encounters with griffons in Spain, check out these photos (courtesy of Bob Loveridge)...



One really important point that needs emphasis whenever vultures (both Old and New World) are discussed is that they most emphatically are not sorry, garbage-eating consumers of leftovers. While it's - of course - true that they eat carrion, vultures are the primary consumers of this enormous resource, out-competing all other carrion-feeders simply by finding and consuming carcasses more rapidly than anything else (DeVault et al. 2003). Lord Geekington covered vultures back in 2009 (sorry, Cameron) and wrote "So forget the image of vultures cleaning up after lions on the savannah - they consume staggering amounts of biomass from carcasses the size of mice to elephants in temperate and tropical environments worldwide (except Australia...)".

Condors and their possible close relatives, teratorns, were previously covered here...

And for more on raptors of all kinds, see...

Refs - -

DeVault, T., Rhodes, Jr., O., & Shivik, J. (2003). Scavenging by vertebrates: behavioral, ecological, and evolutionary perspectives on an important energy transfer pathway in terrestrial ecosystems Oikos, 102 (2), 225-234 DOI: 10.1034/j.1600-0706.2003.12378.x

Gailey, J. & Bolwig, N. 1973. Observations on the behavior of the Andean condor (Vultur gryphus). The Condor 75, 60-68.

Lerner, H. R. L. & Mindell, D. P. 2005. Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution 37, 327-346.

Ward, J., McCafferty, D. J., Houston, D. C. & Ruxton, G. D. 2008. Why do vultures have bald heads? The role of postural adjustment and bare skin areas in thermoregulation. Journal of Thermal Biology 33, 168-173.

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sun-bathing doesn't look likely on this occasion

Why not? Shadows can be seen, so the sun seems to have been shining at the moment when that photo was taken.

I've had some nice encounters with griffons in Spain

Any particular reason why they were (apparently) circling above you? Were they fancying their chances of getting to consume your, erm, biomass?

You might be right about that Torgos. As for the Spanish griffons - funnily enough, these photos were not taken anywhere remote or wild, but in the middle of a town, right next to a supermarket.

I would love to hear some more about the ancestors of these fantastic creatures.
In the Pleistocene there was a large guild of old world vultures (?), cathartid vultures, condors and Teratorns.

But there is very little information about these fascinating birds in the pliocene, miocene, oligocene and eocene period.

Not familiar with European birds, but I think that those in the lower two photos were the star of this show (2004 in East Germany)...

... after that we got the pilots away in the comp and got on with the important business of the day (!). With the help of Sabine and Rolf we rigged the LS1 and I was able to take it on a quick local soaring flight. Off the Wilga at 600m I could see 3 big birds circling in the distance. I went over to them for a closer look and they seemed to be big buzzards. With a wingspan in excess of a metre or so they looked like pretty chunky birds, not the sort to have a disagreement with. After a short while one left and I continued to climb with the remaining two. We were all pretty close and they seemed to prefer sitting behind my wingtip (to ride the vortex) when they could. At times we were flying 5m or less apart. A really special climb as they either chose to stay with me the whole way or are a little less expert than the Aussie raptors (the former I think).

As we approached cloud base I cracked the brakes to stop going up into the cloud, but the buzzards went up into the gloom. Then they started doing something particularly spectactular which I've heard of but never seen. They would fly close together, one above the other, then the top one would roll around onto its back and underneath the other one. They would clasp talons and fall for a while, let go and do it again. When they started this they were well above me and I dropped 300m following them down until they disappeared below...


Vultures have always been my favorite birds, new & old world alike (though technically the New World vultures are storks, not raptors).

I actually saw a cinerous vulture at the prague zoo doing the whole 'drop-wing' pose, but on a cloudy day. I got the impression it was just one of those things animals do without necessarily having an adaptive purpose, like why greyhounds sleep on their backs with all four legs in the air, or why my turtle has been flashing my wife.

Sorry Mokele - NO, New World vultures are _not_ storks. This hypothesis was based on misinterpretation of some molecular evidence and is now out the window (as it has been for a few decades). New World vultures seem to be allied to other falconiforms after all. Search Tet Zoo using 'storks and New World vultures' for more.

I do love vultures, I dont think of them as creatures of ill will, but I have to admit that there is one that I think looks very intimidadting. The Red Headed vulture is what I mean, that combination of black and bright read really makes it look mean and foreboding.

By Tim Morris (not verified) on 24 Sep 2010 #permalink

Stephenk, as a glider pilot myself I'll confirm that encounters with soaring birds are not uncommon.

In the UK where I'm based I've had some very good views of buzzards, the best being once when I was sandwiched in a thermal between a parent bird above and two juveniles below. Usually buzzards rapidly climb past gliders but in this case the juveniles were more keen on chasing each others tails then getting centered in the thermal, so I was able to stay with them for several minutes...unfortunately I didn't have a camera with me that day. Soaring birds can often be a good marker of where the best lift is, very useful on days when the thermals are weak or broken.

Many species of raptor display the talon-grappling behavior you described, often during courtship (but also conflict). It' pretty spectacular to watch. March Harriers but on one of the best talon-grappling displays, but usually at low altitude so they are probably not what you saw. Could well have been buzzards you saw.

Apparently seeing vultures while soaring in Spain is quite common, though I've not been gliding there yet. The only time I've seen vultures in the wild is when I visited a colony of Griffon vultures recently established at the Gorge du Verdun...spectacular is probably the best word to describe them (and the gorge itself).

Vultures and condors also share a habit of curiosity.

In Tibet, when you stop your car and walk out, you quickly see a little dot coming on the sky. It is either Himalayan Griffon or Lammergeier, which make about three circles over your head, and after checking that this activity looks not likely to result in food, glides quickly back the same way to its usual post on the sky.

Another interesting thing is that vultures (and some other raptors to smaller extent) have a sort of aerial roads. They know a network of places - especially cliffs, ridges and bare sunny hills - where regular air uplifting occurs - and follow them as regularly as people follow roads.

Hm, now that you mention it, what DOES fill the carrion cleanup job in Australia? Corvids?

One immediate thought is that the Wedge-tailed eagle Aquila audax might do a lot more scavenging than other aquiline eagles.

Out of curiosity, are there any signs of vulture analogs in Australia's recent fossil record, given how much more megafauna there would presumably be for them to eat, as well as larger predators to bring down the bigger herbivores more frequently?

What does the literature say about vulture predation activities? I know I've read at least one report of a turkey vulture preying on a songbird, and I observed at least one turkey vulture predation attempt (though it was unsuccessful).

Curious to know how frequent those kinds of things are.

By Tor Bertin (not verified) on 24 Sep 2010 #permalink

Those head feathers on that griffon vulture are interesting. Could they provide a artistic or functional model for the "proto-feather" structures on basal coelurosaurs?

By Zach Miller (not verified) on 24 Sep 2010 #permalink

Also, in Florida during the summer I've seen egrets assume the same posture as the Torgos, flapping their throats too.


What does the literature say about vulture predation activities?

It says that the American black vulture Coragyps atratus, in particular, is a pretty serious predator of surprisingly large animals. See this comment, and try to find the references that I cite. (Also see what Darren says about lammergeier vultures in the blog post.)

I've noticed that the Lappet-Faced vulture has a large, hooked beak compared to other vultures. Could this be an adaptation to feeding on the carcasses of thick-skinned mammals like elephants and rhinos?

By gray Stanback (not verified) on 24 Sep 2010 #permalink

I have heard that New World vultures do indeed defecate on their feet as a cooling mechanism. IIRC this was argued as a a character in common with storks.

FYI SACC currently treats New World Vultures as their own order, although of course all that linean rank stuff is a tad arbitrary

By Morgan Churchill (not verified) on 24 Sep 2010 #permalink

Paul B,
I have flown with birds (and used them as thermal markers) many times. Of course that was what I was doing on that, my first trip to Europe. I didn't recognise them then as I had no good access to any sort of field guide, and have always wondered what they really were. The wing shape and white underneath marking is very similar (from memory) to the photos above. The birds I am most familiar with through soaring are the Wedgetail Eagle and the Black Kite [can't lay my hands on my Simpson and Day and don't remember their scientific name]. I have been in a thermal with 15 (that I could count) Black Kites in close vicinity. I have also seen Australian Eagles and Nankeen Kestrel [Falco enchroides] (there was a pair of Nankeens who actually nested at the gliding club for a couple of years, then another pair, which I assume included one of their offspring)

RhysD (and DarrenN),
The Black Kites I mentioned do seem to scavenge. Along with Silver Gulls (!) they were the predominant birds at our local rubbish dump.
I would imagine Wedgetails do scavenge as well. When I was a very small boy they had a very bad reputation with farmers for taking lambs. I recall seeing dead (shot) Wedgetails strung up along fences. I believe that they are protected now and farmers don't complain too bitterly about them, so I assume most of the old stories were based on seeing eagles with dead lambs that probably died naturally or were killed by other predators. (I still think it likely that Wedgetails kill lambs, just that it was an exagerated problem).


Another little taxonomic quibble. NW vultures are indeed more closely related to falconiforms than to storks, but they are not falconiforms, the only real falconiforms being falconids. NW vultures are accipitriforms (I restrain myself here from saying that they're basal accipitriforms), and the evidence seems to show that falconiforms and accipitriforms are not closely related within "land birds".

Once last year, at Big Sur, a group of four California condors flew by about 20 feet over my head. Now that's an impressive bird. And then, this spring in Belize, I saw king vultures: not so big but prettier.

By John Harshman (not verified) on 24 Sep 2010 #permalink

Wedge-tailed eagles do indeed do a lot of scavenging. Whilst driving on the highway from Perth to Carnarvon two years ago, much of the roadkill we saw by the side of the highway was being attended to by one or more eagles. As far as scavengers in Australia are concerned, I'd be positing Thylacoleo and Sarcophilus as past and (at least in Tasmania) present scavengers since the former is thought to have been and the latter is known to be capable of crushing bone.

The drooping wing posture is common in Gyps and Aegypius vultures not only when loafing but as displays of aggression and dominance around carcasses. Lappet-faced Vultures when approaching a carcass will lower their wings and head and rush the Griffons that have gathered. Once scattering them the Lappet-faced stands up straight with wings lax as in the photo and walks away with a slow swagger (and a hint of smug satisfaction) usually without showing any interest in feeding.

Predation behavior has anecdotal evidence mentioned for almost all species of vultures but this is often exaggerated especially in the Condors and Bearded Vulture. The Griffons are among the least predatory of all vultures and are known only to attack living animals when they show signs of distress.

The New World Vultures with their straight toes and short hallux cannot grip or carry anything and would be limited to pinning small animals down with their feet and dispatching them with their beak. As Dartian linked above, the Black Vultureâs boldness makes up for its apparent lack of armament.

Several of the Old World Vultures on the other hand have very strong gripping eagle-like feet especially the four king-style Aegypius vultures. Following Amadon & Bull (1988) the Cinereous (A. monachus), Lappet-faced (A. tracheliotos), Pondicherry (A. calvus), and White-headed Vultures (A. occipitalis) are all very similar and closely allied both physically and behaviorally. The Arabian subspecies of the Lappet-faced Vulture (A.t.negevensis) is very similar to the Cinereous Vulture in plumage, beak color, and in having a downy white head and in its large body size. Hybridization in the middle-east in the past might account for these intermediate characteristics.

Predation is most commonly attributed to the Lappet-faced and White-headed Vultures with a substantial part of their diet apparently coming from hunting and kleptoparasitism. Mundy et al (1992) believed the White-headed Vulture possibly specializes on predation for its food supply and mentioned the most exceptional instances being of a pair killing an Oribi in Mozambique and a group of four bringing down an old Impala in Zimbabwe. Both species are known to raid flamingo colonies to prey on eggs, chicks, and adults. Mundy also mentions many instances of both species have been found on freshly killed and still warm small animals including guineafowl, mongoose and dik-dik. Both species nests are full of remains of a large variety of small mammals, reptiles, and birds suggesting regular predation. In several cases the vulture in possession of a small carcass had an eagle perched nearby (Martial and Tawny usually mentioned), apparently an act of piracy. Jane Goodall mentioned seeing a Lappet-faced Vulture attack an eagle in flight while the latter was clutching a still living jackal.

Below is a link to youtube showing a Lappet-faced Vulture eating a live Black-backed Jackal in the Serengeti. Whether the bird tackled this jackal or found it already injured is not clear from the video.

Mundy, P. et al. 1992. The Vultures of Africa, Academic Press.
Wilber, S. & Jackson, J. 1983. Vulture Biology and Management, University of California Press.

By Bill Unzen (not verified) on 24 Sep 2010 #permalink

Hey Darren,
Another excellent post.
On the topic of maniropteran/avian arms: has anyone ever looked at why stem-maniropteran wrists became oriented to bend 'sideways'? What is the phylogenetic extent of this wrist posture in theropods?
So after walking by someone jogging in an incredibly comical, awkward posture today- arms flapping loosely and asymmetrically at the sides (which also seems inefficient in countering the torque exerted by the hips)- it occurred that while there may be no default arm/wrist posture in (human, at least) bipeds, it may matter significantly to the biomechanics of running and agility. I kind of feel like we humans typically carry our arms with crooked elbows around chest-high, but that exact position and flexion of hand, wrist and elbow varies, particularly the hand/wrist- it kind of requires some individual decision on the part of the user, as it were. There is no natural, relaxed, anatomically enforced posture for the wrist while running, as there is for e.g legs while standing (lock one/both knees). But we humans are only recently derived bipeds and for various reasons we have probably not (conservative statement) perfected it. But, if there is some biomechanically optimal hand/wrist pose, wherein the organism doesn't have the option to settle on a possibly suboptimal pose, perhaps the maniropteran wrist would be it. While running, the arm can be neatly tucked in, while when turning suddenly it can be extended neatly and incrementally to alter the angular momentum of the body. Anyways, any thoughts on the whys of maniropteran wrist posture, which is still so evident in the shape of avian wing today?

Concerning the scavenger guild in Australia

Though Sarcophilus, the australian crows and the wedge-tailed eagle are known scavengers i think that the myriade of monitors are probably the most efficient scavengers.
I remember an australian monitor feeding on a turtle carcass which was so putrifid the flesh was almost liquid.

In another case I saw a Kookaburra eating from a kangaroo carcass.

But we humans are only recently derived bipeds and for various reasons we have probably not (conservative statement) perfected it.

Also, we descend from climbers. Our arms are extremely unusually mobile. Theropods in general were and are incapable of fully extending their elbows and of twisting the forearm (like in locking/unlocking a door).

Moreover, because of our climbing ancestry, we have extremely long limbs and no tail, so we need (to some degree) our arms for balance.

By David MarjanoviÄ (not verified) on 25 Sep 2010 #permalink

@John Harshman

I haven't read the Auk or other reliable source for some time, but I don't remember hearing about Falconiformes being split. Do you have a good source for me to read about it?

By David Houston (not verified) on 25 Sep 2010 #permalink

For a great programme about the environmental importance of vultures I recommend you watch "India's Silent Killer", an episode in the current series of Nature Shock on Channel 5 in the UK. Overall it's a good series and takes a grown up look at the science behind animal events, the last one was about Crocodiles in Kruger NP dying off due to pansteatitis.
The last episode (in the UK)is on Tuesday 28 September.

By David Kelly (not verified) on 25 Sep 2010 #permalink

All last phylogenetic studies split "traditional" Falconiformes into Falconiformes (only with Falconidae) and Accipitriformes (with the rest, Cathartidae incluse or not). Falconiformes (falcons) are nested in a nice Gondwanic clade uniting Passeriformes, Psittaciformes and Cariamae; Accipitriformes in another, maybe of African origin, including Piciformes, Coraciiformes, Trogoniformes, Coliiformes and Strigiformes. Cathartidae are posited in the base of Accipitriformes clade. Maybe Cathartiformes descend from proto-Accipitriformes who crossed Atlantic from Africa to South America near the end of Eocene.

By J.S. Lopes (not verified) on 25 Sep 2010 #permalink

To complete that thought :) (was moving my computer), David- good points about the exceptional mobility of human wrists related to climbing ancestry. But transitioning from a quadrupedal to bipedal form, one would expect the hand to continue to flex such that it splays forward when flexed, as it does in quadrupedal form. Why did it switch to flex in the same plane as the elbow? I mean, xenarthrans walk on the sides of their feet, but that is clearly due to (or which enabled) their signature long hand and foot claws. Why then do theropod hands bend sideways i guess (if all theropod hands do so).

For falconiform polyphyly, try Hackett, S. J., R. T. Kimball, S. Reddy, R. C. K. Bowie, E. L. Braun, M. J. Braun, J. L. Chojnowski, W. A. Cox, K.-L. Han, J. Harshman, C. J. Huddleston, B. D. Marks, K. J. Miglia, W. A. Moore, F. H. Sheldon, D. W. Steadman, C. C. Witt, and T. Yuri. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320:1763-1768.

Which you can get here:

Or you might try the Tree of Life Web Project:

By John Harshman (not verified) on 25 Sep 2010 #permalink

It seems like it might just be coelosaurs that have sideways-bending wrists. pls excuse my lack of knowledge of dinosaur phylogeny and anatomy, that could be wrong..

vultures are the primary consumers of this enormous resource, out-competing all other carrion-feeders

Not over vast areas, though. At least in North America, vultures don't get much above the 50th parallel. They're also restricted temporally, retreating in winter to Mexico and the southeastern U.S.

carcasses the size of mice to elephants

Now I'm curious to know just how important small vertebrate carcasses are to vultures. I assume their major competitors for this resource would be Nicrophorus burying beetles, which share many traits with vultures - exceptional sense of smell, ability to fly long distances, resource partitioning between species and general intent to consume an entire carcass themselves. If vultures are a major consumer of small carrion, perhaps the beetles remain competitive simply by being nocturnal.

Chelydra: you should definitely check out DeVault et al. (1993), cited above - they discuss all of the things you've just mentioned. Data from pellets show that New World vultures eat a lot of shrews and rodents, leading DeVault et al. to note that "small mammal carrion must be available to vertebrate scavengers at least to some degree" (p. 228). As for competition with burying beetles, the data compiled by these authors shows that vertebrates are by far more significant as consumers of carrion, though I'm not pretending that all vertebrate scavengers are vultures.

And, yes, vultures and condors are not ubiquitous... but I think the point is that they are hugely important in the places where they do occur.

the Wedge-tailed eagle Aquila audax might do a lot more scavenging than other aquiline eagles

I'm not familiar with other aquilines, but wedgies are most often seen* on or beside roads feeding on large items of fresh roadkill. When there's a possum or small wallaby on the road, you most often see crows on it; large wallaby to grey kangaroo, you get black kites; red kanga or pig will bring the eagles (anecdotal, not quantitative - though someone ought to have numbers on this stuff). Oddly, I've rarely seen anything feeding on dead cattle.

*(The other places I've seen them were in forested and relatively mountainous parts of the south-east, soaring or kiting over cliff-tops and ridges. You don't see black kites in that region, so the eagles presumably don't specialise so much on larger items)

One time in northern South Australia, a red kangaroo on a rare bend in the road resulted in the deaths of at least three eagles feeding on it, as they have a pretty slow take-off. Especially since seeing that, I've frequently stopped to drag dead roos off the road.

Black kites are certainly the main occupant of the 'vulture' niche in these parts, rarely seen on the ground except at roadkill, though in fact they mainly eat small stuff (I've seen them grab displaying male Lophognathus dragon lizards from my back yard, and got Pogona, Chlamydosaurus and locusts as gut contents of road-killed kites).

Walter Boles has described bits of several extinct raptors from the Mocene of Riversleigh, but we don't know enough about their ecology (the intriguing exception being Pengana, the 'flexiraptor', which convergently shares features of the leg joints with living species that capture prey within crevices and tree-holes).

David- good points about the exceptional mobility of human wrists related to climbing ancestry.

Not so much the wrists as the shoulders and the elbows.

But transitioning from a quadrupedal to bipedal form, one would expect the hand to continue to flex such that it splays forward when flexed, as it does in quadrupedal form.

The hand does not point forward in quadrupedal forms other than therian mammals, sauropods, and apparently some ornithischians. :-) It points sideways. This problem is normally solved by sprawling the forelimbs: the hand points forward when the elbow points outward. The ability to twist the forearms so that the hands can point forward when the forelimbs are held parallel is an adaptation to walking on top of thin branches and came about late in the common ancestry of marsupials and placentals. The monotremes still sprawl.

Putting your hands on a keyboard requires crossing radius and ulna. This ability is not normal.

The sauropods solved the problem by having the ulna grow around the radius so that the radius ends up lying sort of on the medial side (for its entire length, not just part of it!) and the ulna on the lateral side, much like tibia and fibula.

Plateosaurus and Camptosaurus were incapable of holding their hands forward while holding the arms parallel. Camptosaurus appears to have been about as quadrupedal as a large kangaroo, and Plateosaurus was an obligate biped.

Ceratopsids held their hands mostly outwards. The first two fingers pointed forward on average, the third sideways, and the remaining two (pointing sideways and backwards) didn't even touch the ground.

By David MarjanoviÄ (not verified) on 26 Sep 2010 #permalink

What about things like rauisuchians? Did their hands point outward?

By Andreas Johansson (not verified) on 26 Sep 2010 #permalink

Thanks. I've bookmarked the U Florida site. There's some fun reading there.

Back when I went to AOU meetings (in the 70s), Joel Cracraft was my favourite speaker.

By David Houston (not verified) on 26 Sep 2010 #permalink

There are vultures that nest on the English/Humanities building at my school in the spring. Me and my friends like to make jokes about them waiting for the departments to die. Kind of sad, actually...

Re: "Camptosaurus appears to have been about as quadrupedal as a large kangaroo" (D.M., #38):
Not immediately relevant to the point, but my sense is that kangaroos, when moving slowly (e.g. when nibbling at the lawn) are sorta quinquepedal: the gait is move forefeet forward, then support body on proximal tail while lifting the hind feet and moving them forward. (I don't think I've seen a really big kangaroo do this, but at least medium size ones.) I suspect this is NOT a good model for Camptosaurus: it responds to the very special configuration of the Macropod hind limb, with its big foot.

By Allen Hazen (not verified) on 26 Sep 2010 #permalink

John S.:

I'm not familiar with other aquilines, but wedgies are most often seen* on or beside roads feeding on large items of fresh roadkill.

The golden eagle Aquila chrysaetos, at least, occasionally feeds on small roadkill (e.g., hares and foxes).

When there's a possum or small wallaby on the road, you most often see crows on it; large wallaby to grey kangaroo, you get black kites; red kanga or pig will bring the eagles (anecdotal, not quantitative - though someone ought to have numbers on this stuff).

*shudders at the thought of the carnage on Australian roads*

The obvious interpretation of your observation would be that differently-sized avian scavengers prefer differently-sized carrion. However, I can think of two alternative explanations:

-Perhaps it's simply a function of the relative abundance of the respective scavengers, and of the time it takes to consume carcasses? The corvids, which usually are more numerous than either kites or eagels, tend to discover the carcasses first; and, if the dead animal is small, they will usually consume it before larger raptors arrive on the scene and displace the smaller scavengers. (Ditto for kites vs. eagles.)

-On the rare occasions when an eagle is the first (or among the first) to discover a small-sized roadkill item, perhaps the eagle might prefer to simply grab the carcass and transport it somewhere else, to be consumed in privacy? I've heard of one case of a golden eagle which, at the approach of a car, tried (unsuccessfully) to carry away the road-killed hare it was feeding on.

Oddly, I've rarely seen anything feeding on dead cattle.

Odd indeed. Beef is good eatin'.

What about things like rauisuchians? Did their hands point outward?

No idea.

However, some of those beasts were bipedal. What is known of the hands of Postosuchus is tiny.

I suspect this is NOT a good model for Camptosaurus: it responds to the very special configuration of the Macropod hind limb, with its big foot.

Its tail couldn't work like a macropod's, that's clear. I'm talking about how the short forelimb is, as shown in this paper (pdf), adapted to bearing weight, but the range of motion was very limited and twisting the forearm was impossible. Quadrupedal walking (let alone running) would have been difficult, but apparently Camptosaurus stood around on all fours a lot.

By David MarjanoviÄ (not verified) on 27 Sep 2010 #permalink


Oddly, I've rarely seen anything feeding on dead cattle.

Around here, whenever a raven removes the eyes, lips, genitals, perianal tissue.. of a fresh dead cow with surgical precision with its sharp beak, the welfare ranchers all swear that it must've been satanists or space aliens that were the culprit.

By darwinsdog (not verified) on 27 Sep 2010 #permalink

Well my understanding - perhaps inaccurate - is that the skin of some larger mammals (including cows) presents a serious challenge even to a Gyps beak and that Gyps vultures in Africa or Spain will do like those ravens until a Torgos or Aegypius shows up to tear the thing open. Perhaps this explains the uneaten Australian cows.
One thing that does surprise me though, when you put them all together is that the beak of that condor at the top looks pretty mincy compared to either of the old world vultures underneath. The Californian condor's beak seems to be a similar size and shape to the Andean. I thought this might be an illusion created by the wattled and bulbous condor heads but a google image search for the skulls seems to confirm it. So why no flesh-tearing beaks for the condors? Are the New World prey just not thick-skinned enough? What about Teratorns?

By farandfew (not verified) on 27 Sep 2010 #permalink

Wow, badly timed vacation on my part.

They're also restricted temporally, retreating in winter to Mexico and the southeastern U.S.

Only about half of the turkey vultures on the East Coast migrate - I've seen them during winter in New England.

What about Teratorns?

They had skulls adapted for swallowing live prey whole. Facultative scavenging isn't out of the question, but it's doubtful they could tear through the skin of large animals.

So teratorns were giant storks too? Ecologically I mean. Even though they still looked like raptors? I can't get hold of the Campbell and Tonni paper on the skull for some reason but the one on locomotion (free online) seems to suggest this. It seems like a surprising conclusion. I mean Azhdarchids kind of look like storks (except that they're pterosaurs obviously) while Teratorns really don't (except obviously they do because they're birds).
I mean if something can look basically like a raptor but behave like a stork then...well.. why do storks look like storks? And not like raptors?
I duz science talking good, heh?

By farandfew (not verified) on 28 Sep 2010 #permalink


So teratorns were giant storks too? Ecologically I mean. Even though they still looked like raptors?

In principle at least, there's nothing particularly strange about that. Accipitriforms are not evolutionarily constrained to remain 'raptorial' in their feeding habits. For example, the honey buzzards Pernis are mostly insectivorous and the palm-nut vulture Gypohierax angolensis is mainly a frugivore.

I mean if something can look basically like a raptor but behave like a stork then...well.. why do storks look like storks? And not like raptors?

Because usually, it takes a while for morphology to catch up with ecology (so to speak).

Interesting! I wondered why there is no Marabou equivalent in tropical Americas and whether Jabiru could be prehistoric scavenger which turned to live prey after megafaunal extinction. But it seems that this niche was filled by teratorns.

I don't think teratorns were stork-like in the strict sense. Sure, they may have eaten living prey, and they may have done more walking than cathartids and aegypiine vultures do, but I don't see any evidence showing that they were behaving in stork-like fashion. Anyway, in response to comment 50, there were marabous in South America: the large species Leptoptilos patagonicus was described from the Miocene of Chubut Province in 2008. See...

Noriega, J. I. & Cladera, G. 2008. First record of an extinct marabou stork in the Neogene of South America. Acta Palaeontologica Polonica 53, 593â600.

Could the Jabiru be to a lesser extent Marabou's equivalent
in South America ?

By Longfinmako (not verified) on 29 Sep 2010 #permalink


the honey buzzards Pernis are mostly insectivorous and the palm-nut vulture Gypohierax angolensis is mainly a frugivore

good point

Because usually, it takes a while for morphology to catch up with ecology (so to speak)

I feel that's maybe not so much of a good point. Argentavis is Upper Miocene and I feel like that's quite a long time to not evolve longer legs and a straighter bill if they would have been useful. And I'd forgotten about Marabous. Not only is it allegedly possible to be a vulture (-ish thing) to behaves more like a stork than a vulture, it's also definitely possible to be a stork that behaves and looks a lot more like a vulture than most storks do. And it seems they've been around since at least the Miocene too. Any measurements of divergence times for the Honey Buzzards?

But anyway the Marabous clearly present a problem to the idea that, just because a bird can only swallow things whole and can't tear flesh, then it must be a catcher of live prey as opposed to a scavenger.
So maybe the teratorns were quite vulture-like scavengers after all but just not adapted to tearing open carcasses? But then why weren't there any New World birds adapted to tearing open thick-skinned carcasses? Or could a lesser-known Teratorn have been doing so.

By farandfew (not verified) on 30 Sep 2010 #permalink


Any measurements of divergence times for the Honey Buzzards?

Not really, at least not AFAIK. Honey buzzards have no fossil record to speak of, but on morphological grounds, Pernis has traditionally always been considered a 'basal' accipitrine. And molecular data mostly support that contention - see, e.g., Gamauf & Haring (2004) and Griffiths et al. (2007). In other words, the extant honey buzzards seem to belong to a raptor lineage that diverged very long ago (probably in the Paleogene).

the Marabous clearly present a problem to the idea that, just because a bird can only swallow things whole and can't tear flesh, then it must be a catcher of live prey as opposed to a scavenger.

That problem may actually be more illusory than real. I rather suspect that we tend to somewhat overestimate the extent to which marabous (for simplicity, I'll refer here to all Leptoptilos species collectively as 'marabous') rely on scavenging. They are really not that vulture-like in their habits, I'd say.

Marabous do, of course, scavenge to some extent. But large game carrion is hardly their main source of food. Like most ciconiids, marabous are first and foremost predators of small vertebrates ('small', in their case, meaning up to the size of an adult flamingo or so) that they catch both on land and in the water. As for their scavenging, marabous typically feed on small carrion, such as dead fish, prey items that they pirate from other birds, or (nowadays) stuff that they find at garbage dumps. Large animal carcasses are not really their speciality; their feeding on them is more occasional and opportunistic.

I suspect that our perceptions of marabou feeding habits are overly influenced by 1) nature documentaries which so often show them squabbling with vultures at megafaunal carcasses, and 2) their 'bald' heads, which have traditionally been thought of as specific adaptations for scavenging on large animal carcasses. As Darren wrote in the main post, the idea that scavenging habits are the main reason for the loss of a feather covering on the head and neck is a doubtful explanation for vulture baldness; for marabous, that explanation seems even more unsatisfactory. There are non-scavenging stork species (the wood stork and the jabiru) that also have naked heads. And, thanks to their long bills, when they do feed on large animal carrion marabous don't usually need to stick their heads or their necks deep into the body cavities anyway. Thermoregulation would thus seem like a more likely explanation for the baldness of marabous (and those other storks).

To put it differently, I don't think that marabous have 'failed' to evolve a hooked, vulture-like bill that's suitable for scavenging. I think it's more likely that because they're not really primarily scavengers, there just hasn't been any strong selection pressure during their evolutionary history to evolve such a bill.

But then why weren't there any New World birds adapted to tearing open thick-skinned carcasses? Or could a lesser-known Teratorn have been doing so.

Or a phorusrhachid, perhaps?


Gamauf, A. & Haring, E. 2004. Molecular phylogeny and biogeography of honey-buzzards (genera Pernis and Henicopernis). Journal of Zoological Systematics and Evolutionary Research 42, 145-153.

Griffiths, C.S., Barrowclough, G.F., Groth, J.G. & Mertz, L.A. 2007. Phylogeny, diversity, and classification of the Accipitridae based on DNA sequences of the RAG-1 exon. Journal of Avian Biology 38, 587-602.

Further to my comments at #37, some observations from a drive of several hundred km through the Gulf country yesterday: a moderate amount of fresh roadkill (yes, the absolute quantity of carnage is shocking; but the density of roads and traffic relative to land area are very small compared to the places where most of you live) attended by flocks of crows, kites and eagles more or less in line with what I said before.

It's around dusk that the roos come out to feed on the roadside and when most of the carnage happens, but there are cattle about at any time of day and night (and it has generally not been economically viable to fence off the roads, only separate paddocks with grids and occasionally gates). On these roads, much of the traffic is very large trucks with three trailers (road trains) supplying, among other places, Century mine near Lawn Hill; they do not brake for animals on the road. We did see a large flock (roughly 50) of kites around a cow... or approximately half a cow; lets just say the tough skin of the rear half no longer presented an obstacle to their beaks. Saw no eagles for most of the day despite plenty of large carcasses, then relatively late in the day (further south) three on a large kangaroo at the roadside (and around sunset, one more that swooped out of nowhere across the road and nearly brushed the windscreen with its wing).

Dartian's suggestions (#43) make perfect sense, but note that our crows (Torresian crows, nearly raven-sized) mostly travel in discrete mobs at relatively low altitude, so they're not nearly as visible as the soaring kites even if they are more abundant.

By John Scanlon, FCD (not verified) on 01 Oct 2010 #permalink

Funny. I took a picture of a similarly posed Vulture last summer at the Atlanta Zoo. Such amazing animals (and personally I think they are adorable)