Posted by: Rob Viens | July 12, 2013

Darwin’s Naked-Headed Death Eaters

With a long trip on the horizon, Darwin was taking advantage of some time in “civilization”, i.e., a place were he could find some of the familiar supplies and services. His sole entry for the past two days states:

“Spent the greater part of these two days in the city, transacting business.” (July 11/12)

But there is still plenty to share from Darwin’s collecting trips in Maldonado, so today I thought I’d elaborate on a few more birds – specifically carrion birds.

Carrion birds, as Darwin refers to them are birds that feast on dead meat.  A classic example of these birds are vultures, and, in fact, two of the birds Darwin describes today are types of vultures. He refers to at least four species of carrion birds  in Voyage of the Beagle – the caracara, turkey buzzard, gallinazo (black vulture) and condor.  He doesn’t meet the condor for a little while, so I’ll concentrate on the first three. (The condor, another type of vulture, deserves its own post anyway!)

Southern Crested Caracara (Caracara plancus)

There are 11 species of caracara in the Americas, though most of them are found in northern or southern South America – i.e., not in Uruguay. Darwin describes several species of caracara, however, modern distribution would suggest that he was primarily referring to the  Southern Crested Caracara (Caracara plancus). Caracara plancus is only one of two living species of caracara in the genus Caracara – the rest are extinct – either recently, such as the Guadaloupe Caracara , or prehistorically. Some prehistoric remains have even been found in California’s La Brea tar pits (where they were probably caught while trying to feast on carrion). One other item of note – in Darwin’s time these birds were classified in the Genus Polyborus – hence the use of he term in his descriptions. (In Voyage of the Beagle, Darwin also describes the Chimango caracara (Milvago chimango) and some caracara observed in the Falklands.  However, since these are from other parts of the trip, I’m not going to write about the, today.)

Southern Crested Caracara near Buenos Aires (from Wikipedia Commons)

Southern crested caracara

Darwin spends some time describing this opportunistic raptor, so I’ll let you read a few of his observations for yourself (all quotes from Voyage of the Beagle):

“The Caracaras are, from their structure, placed among the eagles: we shall soon see how ill they become so high a rank. In their habits they well supply the place of our carrion-crows, magpies, and ravens; a tribe of birds widely distributed over the rest of the world, but entirely absent in South America.”

“After feeding, the uncovered craw protrudes; at such times, and indeed generally, the Carrancha is an inactive, tame, and cowardly bird. Its flight is heavy and slow, like that of an English rook. It seldom soars; but I have twice seen one at a great height gliding through the air with much ease. It runs (in contradistinction to hopping), but not quite so quickly as some of its congeners. At times the Carrancha is noisy, but is not generally so: its cry is loud, very harsh and peculiar, and may be likened to the sound of the Spanish guttural g, followed by a rough double r r; when uttering this cry it elevates its head higher and higher, till at last, with its beak wide open, the crown almost touches the lower part of the back. This fact, which has been doubted, is quite true; I have seen them several times with their heads backwards in a completely inverted position.”

“Azara states that several Carranchas, five or six together, will unite in chace of large birds, even such as herons. All these facts show that it is a bird of very versatile habits and considerable ingenuity.”

Southern Crested Caracara in Brazil (from Wikipedia Commons)

Southern crested caracara in flight

True to form, Darwin was not afraid to describe the taste of the Chimango caracara – though it would appear this is not one that he ate himself:

“The sealers say that the flesh of these birds, when cooked, is quite white, and very good eating; but bold must the man be who attempts such a meal.”

Turkey Vulture (Cathartes aura)

The turkey vulture (or turkey buzzard as Darwin calls it) can be found throughout the Americas – from southern Canada all the way to Tierra del Fuego. It is one of seven species of New World vultures (all part of the Cathartidae family).  Interestingly, they are not taxonomically related to the Old World vultures.  We have convergent evolution to thank for the fact that the two families of birds both evolved “vulture” characteristics.

Turkey Vulture in Uruguay (from Wikipedia Commons)

Turkey vulture

Regarding the turkey vulture Darwin notes:

“It may at once be recognised from a long distance, by its lofty, soaring, and most elegant flight. It is well known to be a true carrion-feeder. On the west coast of Patagonia, among the thickly-wooded islets and broken land, it lives exclusively on what the sea throws up, and on the carcasses of dead seals.” (Voyage of the Beagle)

Unusual in birds, turkey vultures have a well-developed sense of smell, which they use to detect gases released by rotting meat. Also uncommon for birds, these vulture lack vocal organs (a syrinx), and therefore make very limited sounds – mostly just “hisses and grunts”.

Turkey Vulture in Florida (from Wikipedia Commons)

Turkey vulture in flight

Black Vulture (Coragyps atratus)

In his writings Darwin refers to a third carrion eater from Uruguay which he calls a Gallinazo.  It would appear that Gallinazo is the Spanish name for vulture, and based on the description Darwin provides, I am fairly confident that he is referring to the black vulture – a smaller relative of the turkey vulture (both are in the Cathartidae family). Darwin writes:

“The Gallinazo generally prefers a humid climate, or rather the neighbourhood of fresh water; hence it is extremely abundant in Brazil and La Plata, while it is never found on the desert and arid plains of Northern Patagonia, excepting near some stream. … These vultures certainly may be called gregarious, for they seem to have pleasure in society, and are not solely brought together by the attraction of a common prey. On a fine day a flock may often be observed at a great height, each bird wheeling round and round without closing its wings, in the most graceful evolutions. This is clearly performed for the mere pleasure of the exercise, or perhaps is connected with their matrimonial alliances.” (Voyage of the Beagle)

Black Vulture in Florida (from Wikipedia Commons)

Black vulture

One interesting things about both turkey and black vultures – when faced with a dangerous predator they vomit up undigested meat.  Really – nothing dulls the apatite like the putrid smell of rotting meat. (It also makes it easier for the vulture to take off and fly away, and if it hits the predator, the stomach acids may even hurt.) Other interesting factoid – both vultures have 40 pairs of chromosomes, compared to humans which have a mere 23 pairs.

Notice that all three of these carrion-eating species have naked heads. Can you guess why?

Yup – when you stick your head in a dead carcass, the last thing you want to end up with is a bunch of feathers covered in blood, rotting meat, sinew and associated bacteria. Let’s face it – a bare head, is a much cleaner and sanitary way to eat dead meat.

In talking about the caracara, Darwin summarizes the stigma often associated with all carrion eating birds and the slight unease they tend to bring out in humans:

“These false eagles most rarely kill any living bird or animal; and their vulture-like, necrophagous habits are very evident to any one, who has fallen asleep on the desolate plains of Patagonia, for when he wakes, he will see, on each surrounding hillock, one of these birds patiently watching him with an evil eye” (Voyage of the Beagle)

Of course, not everyone fears or dislikes the death-eaters. I am reminded of the words of Ed Abbey, who regularly gave kudos to his favorite carrion birds:

“Let us praise the noble turkey vulture: No one envies him; he harms nobody; and he contemplates our little world from a most serene and noble height.” (Ed Abbey)

Somebody has to defend the poor vultures – after all they serve an important function cleaning up all those dead things lying around the ecosystem … (RJV)

PS – An interesting pop-culture aside… “Carrion Birds” are a category of pet in World of Warcraft with the ability to emit a “demoralizing screech”.  Fun as that may sound, I’m guessing this is not something Darwin would have though much of.  I suspect he would prefer being out and about in the real world :).

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Responses

  1. “I’m guessing this is not something Darwin would have though much of. I suspect he would prefer being out and about in the real world.”
    Who knows how many Darwins have invested all their curiosity in the gaming universe rather than into the actual universe around them at this point?

  2. Good point! I think there are a lot of good aspects to gaming (I am a big fan of Jane MacGonigal’s ideas on using games to solve real-world and personal problems) but I suspect that inspiring people to become naturalists is not really one of the positives. I suppose it could hone some observation skills and require people to be good at making connections with the clues they might find in a game… Some potential transferable skills, anyway. – Rob


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