Hello, I'm Daven Hiskey, you're watching the TodayIFoundOut YouTube channel.
In the video today, we're looking at why vultures don't get sick when they eat dead animals.
While it's important to note that many animals eat carrion, vultures are fairly unique in
that they're able to eat carrion that has succumbed to the effects of decay and disease,
a feat few stomachs in the animal kingdom can match.
As an idea of just how ridiculously hardy vultures are, experiments have shown that
they are all but immune to botulism and that they can happily chow down on the flesh of
an animal coated in Bacillus anthracis which is better known as the bacteria that causes
anthrax!
They also have no problem eating an animal infected with rabies, hog cholera and numerous
other diseases that would ultimately be lethal to most other scavengers.
So how do they do it?
Vultures are able to comfortably eat diseased carrion thanks in large part to their highly
acidic gastric juices which are sufficiently strong enough to kill most bacteria before
they ever become an issue.
For example, as you probably remember from high school chemistry, the pH scale goes from
0 to 14, with 0 representing a highly acidic substance, 7 representing an approximately
neutral one, like pure water, and 14 representing a highly alkaline one.
While the pH of human stomach juice can vary quite dramatically depending on what you've
eaten, it tends to stay between around 1.5 and 3.
In contrast, the stomach acid of a turkey vulture (one of the hardiest members of the
vulture family) has a pH of almost 0.
It should be noted here that the pH scale is logarithmic, which means "each whole pH
value below 7 is ten times more acidic than the next higher value."
In other words, in the extreme a turkey vulture's stomach acid could technically be in the ballpark
of 1000 times more acidic than yours at a given instance.
In fact, it's so acidic that it can dissolve many metals.
For further reference, battery acid has a pH of about 0.8.
Even when bacteria does survive the gauntlet that is the turkey vulture's digestive system,
it then has to compete with its amazing immune system.
In regards to the latter, vultures are noted as having one of the "strongest immune systems
of all vertebrates" and there are few food-borne diseases that truly pose a threat to it.
As for why humans don't have the same abilities, vultures spend almost all of their eating
time in close proximity to decaying, sometimes disease filled flesh, so it's understandable
that members of their ancestry who could handle these sorts of things better would, over time,
dominate the species' gene pool and be able to eat progressively more decayed flesh without
consequence.
Humans, on the other hand, spent many thousands of years using their brains to develop ways
to avoid long dead, uncooked, rotting flesh.
That said, humans can eat raw meat provided it's very fresh and human gastric acid is
strong enough to kill many types of microbes, but there are some bacteria that have no problems
surviving our digestive juices, such as the kind that causes ulcers see our video on the
subject here which covers the Fascinating Saga of Nobel Prize Winner Dr. Barry Marshall
and His decades long Fight to Convince the Medical World What Actually Causes Ulcers.
Of course, there is a point at which even a vulture will say no and flesh will be deemed
too putrid or foul to eat.
However, this doesn't necessarily stop the vulture from eventually eating some of the
remains.
For example, the bearded vulture can live on a diet of 70%-90% bone if it needs to.
In fact, the ability to thrive on this diet is a huge boon for them in lean times as bones
contain a significant amount of calories and will last indefinitely, unlike flesh.
So long after the flesh has gone, the remaining bones are still fair game for the bearded
vulture.
Perhaps the most surprising fact about vultures is that despite their near-universal reputation
as disease carrying pests, they are considered by experts to be the exact opposite and it's
observed that when vulture populations decline in an area, the rate of disease will usually
go up, sometimes dramatically.
Why?
As we've already covered, vultures' digestive systems kill off most microbes present in
carrion making them "dead-end hosts".
So if a vulture eats a diseased animal, the spread of the disease ends there because it
will likely be neutralised by the vulture's body.
This, combined with the vulture's propensity for picking carcasses completely clean, means
that in areas with a lot of vultures, the risk of disease spreading from dead bodies
is relatively low.
However, when a vulture population is displaced, the rate of disease will climb as the bodies
of animals are inevitably left to rot and are consumed by, not dead-end hosts, but potential
carriers.
Further, vultures notably urinate and defecate all over themselves while they eat which,
thanks to the highly acidic nature of their bodily waste, kills most bacteria that makes
its way onto the vulture's legs.
This also has the side effect of sterilising the area around the carcass, also stopping
disease from spreading.
To illustrate what can happen without the vultures in some areas, in India, a massive
decline in vulture populations (such as 80 million white-rumped vultures in the 1980s
vs. only a few thousand now) led to an explosion in the population of feral dogs (estimated
to be about 18 million today in India) and rats with whom the vultures formerly competed
for carcasses.
These animals, unlike the "dead-end" vultures, are vectors for numerous diseases including
rabies.
The remains of the carcasses that were formerly picked clean by the vultures are also now
contaminating water supplies causing further disease issues.
This is more of a problem in India than it would be in many other nations as only about
4% of their 500 million or so cattle are eaten by humans when they die, with the rest in
the past primarily being eaten by vultures.
This has become such a widespread issue that significant research was done to determine
why the vultures were dropping dead.
In the end, it was determined by Dr. Lindsay Oaks et al in 2003 that it was the anti-inflammatory
drug diclofenac that was highly toxic to vultures.
This drug was relatively commonly given to livestock, the carcasses of which the vultures
would eventually eat.
Given the many thousands of extra human lives lost per year in India due to the vulture
population decline, diclogenac was banned in India in 2006 with a substitute being developed
called meloxicam that is not toxic to the vultures.