New World Vultures; something entirely different

Pretty much wherever you go in South America (and a fair bit of North America too I understand) there seems to be a vulture (or several) overhead, or just loafing about. 

Turkey Vulture Cathartes aura, Pisagua, northern Chile.
Typically, this one was soaring along the coast line on big broad wings. The bare head, typical of all American
vultures (and most Old World ones) both prevents contamination of feathers while feeding on - or in - a carcass,
and exposes the skin to dehydration and UV light to kill bacteria.
It is also a means of shedding heat where necessary.
Another characteristic of all vultures is the hooked bill.

But while the vultures encountered in parts of Africa and Asia behave almost identically and look very similar indeed, this is due to a shared lifestyle in two quite unrelated bird groups. If you didn't know that, there's no need at all for any embarrassment - many professional ornithologists have been unwilling to accept it too, though the great English zoologist Thomas Huxley back in 1876 saw that the New World vultures were quite different from all other birds of prey. This view was confirmed by the radical DNA-based reassessment of all bird group relationships by US scientists Charles Sibley and Jon Ahlquist in the 1970s and 80s, and since refined.

White-backed Vultures Gyps africanus, northern Cameroon.
These are typical Old World vultures, and closely resemble their American equivalents in appearance
and behaviour, living almost exclusively by scavenging carcasses.
However unlike the Americans, these are part of the huge line of birds of prey - hawks and eagles. 

So, what are the New World vultures then? Well for a start they're apparently in an entire Order of their own, derived from a stork-like ancestor. (However even now there is dissent, with some authorities believing that they actually do belong in the same Order as hawks and eagles, but separated very early in the history of the group.)

Marabou Stork Leptoptilos crumenifer, Lake Victoria, Uganda.
This big African stork regularly joins vultures at carcasses, and it is not hard to imagine a similar stork
being the ancestor of the New World Vultures. The two groups share many skeletal (in both skull and other bones)
and muscular characteristics.

A shared characteristic of New World Vultures and storks is the unusual habit of defecating liquid onto the
legs to assist in keeping cool. This Black Vulture Coragyps atratus, on the beach on the island of Chiloé
in southern Chile, seems to have been practising this somewhat off-putting behaviour (though keeping cool
isn't a priority in this part of the world!). One of the few consistent obvious differences from Old World vultures
can be seen here too, in the flat feet, which are relatively weak, and a hind toe which is basically useless
in grasping.

Another physical difference is in the beak, though my pictures don't show it. There is no separation of the nostrils, so from exactly side on you can see right through the beak of an American vulture!

Nor is it simply that the two lines of vulture arose in different parts of the world and stayed there. Old World vultures were found in the Americas until very recent times. Fossils from the Le Brea tar pits in California, of vultures which were trapped trying to feed on other victims, tell us that they were present until only 10,000 years ago. On the other hand, while New World vultures used to live in the Old World, there is no fossil record more recent than 20 million years. So in the Americas at least, the two groups lived side by side well within the time of human occupation.

There are seven species of vultures in the Americas. The only one restricted to North America (and the only one I can't illustrate here) is the Critically Endangered Californian Condor Gymnogyps californianus. Four are restricted to South (plus in two cases Central) America, and two extend into North America - indeed the Turkey Vulture breeds from Canada to Tierra del Fuego.

All are primarily scavengers of carcasses, though the smaller species (including Turkey and Black Vultures) do take a range of small prey, including insects, small lizards, nestlings and turtle hatchlings. Curiously, only the three species in the genus Cathartes - Turkey Vulture and two yellow-headed vulture species, which we'll meet shortly - are able to find food by smell. The others must follow them to find food which is hidden under a canopy. The sense of smell of those three species is remarkable, and almost no animal dies in the forest without the vultures soon finding it. 

The authoritative Handbook of the Birds of the World states that they "are the major meat-consuming animals in the forests, probably taking more food than that taken by all of the predatory animals combined".

Andean Condors Vultur gryphus on the carcass of a young Guanaco, probably killed by
a Puma the previous night. This was a remarkable sight, with at least a dozen of the huge birds
present - there was certainly not enough food present for all.
In earlier times when condors (both species) were far more abundant they played a key role
in opening large carcasses which the smaller species could not otherwise access. 

Black Vultures on cow carcass, Pantanal, Brazil. There's not much action here because their bills
are too weak to access the bonanza. No condors here, and only King Vultures locally would have
a chance at such a tough hide, and they are scarce. The Black Vultures must wait for mammalian scavengers
to start the job for them. It is probably because of this that they take more live prey (all small and 'safe')
than other vultures. They must also wait until larger birds (and mammals) have finished, and specialise
in cleaning up scraps left on the skeleton when others have finished with it.
Like the condors they can't smell, but their eyesight is good and in open country they are often the first on the scene.

Greater Yellow-headed Vulture Cathartes melambrotus, Tambopata River, southern Peru.
This species is a rainforest specialist, relying on its nostrils to find hidden corpses beneath the foliage.
(Despite the name, the head colour of the two yellow-headed vultures varies considerably between individuals.)
As mentioned, they find any dead animal on the ground quickly - and this is as well because,
contrary to common supposition, they are not fond of over-ripe carcasses.

The great US nature-painter John Audubon failed to appreciate this in the 1820s when he ventured into field experimentation. Trying to determine whether Turkey Vultures had a sense of smell, he hid a rotting pig carcase in a gully and watched the vultures, which soared overhead and moved on. He concluded that the birds couldn't smell the odiferous hidden body - what he should have considered is that they could smell it perfectly well, and didn't like it at all! Four days of ripening is about the limit of what they'll eat (though carcass less than a day old is hard for them to detect). Sadly, Audubon's foray into ornithological research pretty much killed experimentation into the olfactory senses of birds for the next 150 years.

All vultures spread their wings out to catch the sun, especially (but not only) in the morning. This is in part because some of them drop their temperature at night to save energy, and this is a cheap way of raising it again. There is another reason too; hours in the air soaring can bend the flight feathers upward, and by sunning on landing they can soften the keratin so that the original feather shape is regained more quickly.

Black Vultures catching the morning sun, above and below, Amazon River, northern Peru.

We'll finish with a brief introduction to the six South American species, some of which we've already met. By far the largest is the mighty Andean Condor, which can have a three metre wingspan and weigh up to 15kg, which seems to be the cut-off point mechanically for the largest a bird can be and still fly. Unlike ‘true’ birds of prey male condors are larger than females. Adults are black with a white collar; younger birds are brown (see the photo above, with a red-headed male to the left and a couple of young birds on the right). 

Female Andean Condor, Colca Canyon, northern Peru (this is probably the best place outside of
Patagonia to see this magnificent species - see here for more about it). Females have black heads.
The size, fingered wings and black and white patterning make this bird unmistakable.

Like all vultures, condors save energy by soaring on rising air currents - at Colca Canyon they roost in the depths of the canyon and rise with the morning air. Large vultures don't have the musculature to maintain powered flight for extended periods, but can cover huge distances without flapping and using minimal energy.

Andean Condors rising out of Colca Canyon on the morning thermals.

Andean Condors don't breed until five years old, then produce only one egg every second year. This is a strategy that relies on very low adult mortality, so persecution by pastoralists has been disastrous for them.

Next in size is the King Vulture, huge (unless alongside a condor!) with a two-metre wingspan and weighing up to four kilograms.

King Vulture, dwarfing a Black Vulture, catching the morning light in Brazil's Pantanal.
It is a beautiful bird, mostly found in forests, but uses open country in places like the Panatal.
Their size and huge bill means that they can open carcasses that the others in their area can't;
they also seem to focus on tough parts like skin and tendons and sinews, for which there is minimal competition.

The two yellow-headed vultures were only separated from each other in the 1960s. An important difference between them is in habitat - Greater Yellow-headed Vultures are forest specialists, while Lesser Yellow-headed Vultures Cathartes burrovianus are associated with open country - grasslands and wetlands. They are not otherwise easy to distinguish because both are variable, though there is a definite size difference.

Greater Yellow-headed Vulture, southern Peruvian Amazonia.

Lesser Yellow-headed Vulture, Pantanal, Brazil.
The head may be pure yellow, or with patches of blue (as here) or orange.

Turkey Vultures are probably the most familiar, being found across most of the Americas, from desert coasts to tropical rainforests. 

Turkey Vulture preening, Ballasteras Islands, Peru. They are commonly found in such coastal situations where the
desert meets the sea. While almost exclusively carrion eaters, Turkey Vultures in such situations will eat booby eggs
and fish regurgitated by boobies. They are more interested however in dead fish, seabirds and sea lions.
Overall they are timid birds, and while often first on a carcass due to their excellent sense of smell, they
will retreat when competition arrives and come back later.

Turkey and Black Vultures, and Kelp Gulls Larus dominicanus on the beach of western Chiloé Island,
southern Chile. This is a common sight.

Black Vultures are found across most of South America and north along most of the length of the US east coast.

Black Vulture, Lima, Peru. The slender, relatively weak bill is evident here,
as is the characteristic warty head and neck skin.

If you're not predisposed to like vultures, I don't suppose I've persuaded you to do so. However perhaps we can agree that they are fascinating birds, and without their massive clean-up role, their part of the world would be a much less healthy place. 

King and Black Vultures, Tambopata River, southern Peru.

THERE WILL BE A HIATUS IN THE BLOG FOR A FEW WEEKS NOW,
WHILE I'M IN AFRICA (EAST AND SOUTH); I'LL COME BACK WITH LOTS
MORE BLOGGABLE MATERIAL THOUGH.
I HOPE YOU DON'T FORGET ME MEANTIME!

NEXT POSTING THURSDAY 20 JUNE
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