Monday, 6 April 2015

My vulture's got no nose

. . . Q. how does he smell?
A: "Terrible".
It may be from his habit of urinating on his legs either a) to keep them cool or b) to kill off the bacteria from the carcasses he wades through or c) both.  I was having a rant at my rellies for getting into a naming-of-parts argument that could be quickly resolved by using Latin/Linnaean binomers instead of common language when referring to members of the natural world.  But they would not be the first to get in a tizz-wozz because the two parties were talking about different things.

There are two families of vultures a) Old World Accipitridae and b) New World Cathartidae. The two families are related but not closely and many would put them into different Orders as well as different families. Orders are a higher classification equivalent to mammalian primates vs rodents vs carnivores. In the early 19thC when science started to be widely applied to the study of birds, there was a ding-dong war by letters about how vultures found something good to eat.

One school led by John James Audubon held that birds in general and Turkey Vultures Cathartes aura [L] were unable to smell and hunted solely with their eagle-eyes.  The metaphor is appropriate because eagles are also members of the family Accipitridae. The assertion of Audubon, the most famous birder of the 19thC, perhaps the most famous birder of all time, had weight.  We've met him before counting passenger pigeons Ectopistes migratorius and he is tribbed by the enormously successful [$90million a year!] bird-hugger's Audubon Society.  But he didn't rely on ex cathedra comment, in 1826 he carried out an 'experiment' putting out a) an odour-free stuffed deer-skin in plain sight and b) a decidedly dead, indeed rank, pig covered up with brush; and sat some distance away with a telescope. It's a real crap experiment - more of an anecdote - with not enough data, too many variables, and expecting one particular answer. His vulture savaged the deer and ignored hog . . . case proved . . . not!

There is even a suggestion that Audubon, not knowing his hawks from a handsaw [Shagspere], made his observations on the Black Vulture Coragyps atratus,[L] rather than Cathartes aura. Other birders, notably Charles Waterton, waged a "Vultures can SO smell" campaign over the next several years but their experiments were not notably better structured than Audubon's. Over time, the Can-Smell lobby has more or less won the war but only for New World vultures, Old World vultures are widely seen as being if not ansomic at least micro-osmic. So when a great white hunter wrote from his tree-house in the Serengeti, his remarks had nil bearing on what actually happened in the Rockies. For edutainment, and not only for twitchers, you could read the published version of Ken Stager's 1960 PhD thesis The Role of Olfaction in Food Location by the Turkey Vulture [pdf warning] on the matter. So it shows that, even if you use Latin names, you can still be barking up the wrong tree. It transpires that the reason Audubon's vultures avoided the vaporising dead pig is because they thought it didn't smell very nice - they prefer more recently killed meat - not hung quite so long. My father's Uncle Hardress used to hang his pheasant until the carcase dropped off its own feet. Stager also found that the chemical compound which vultures followed up-wind was ethyl mercaptan - the same thing that is added to natural gas so leaks are detectable.

I think I feel a final year research project coming on: searching bird genomes for olfactory receptor genes.


No comments:

Post a Comment