During the Niku IIII expedition, forensic anthropologist Dr. Karen Burns
conducted an experiment intended to provide some initial rudimentary data
on the rate at which dead animals decay in the island environment. Our
interest in the subject stems from the discovery, in 1940, of the partial
skeleton of a castaway suspected at the time as being that of Amelia Earhart
(see Amelia Earhart’s Bones and
Shoes).
In his April
1941 report (see The
Bones Chronology), Dr. David Hoodless, the British colonial
physician who examined the bones, stated that the remains found
on Gardner Island consisted of: |
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1. |
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a
skull with the right zygoma and malar bones broken off; |
2. |
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mandible
with only four teeth in position; |
3. |
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part
of the right scapula; |
4. |
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the
first thoracic vertebra; |
5. |
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portion
of a rib (? 2nd right rib); |
6. |
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left
humerus; |
7. |
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right
radius; |
8. |
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right
innominate; |
9. |
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right
femur; |
10. |
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left
femur; |
11. |
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right
tibia; |
12. |
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right
fibula; |
13. |
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the
right scaphoid bone of the foot. |
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Dr.
Hoodless noted that “From this list it is seen that less than
half of the total skeleton is available for examination.” Considerably
less than half. Officially there are 206 bones in the human body, but
that includes 2 kneecaps, 6 tiny bones in the ears, 54 bones in the hands
and 52 bones in the feet – so 79 of the 92 larger bones were missing,
including 10 of the major bones, such as the left innominate (the left
half of the pelvis). Where did they go? |
In
a telegram to his superiors dated October 17, 1940 (see The
Bones Chronology), the colonial officer who found the bones, Gerald
Gallagher, wrote:
All
small bones have been removed by giant coconut crabs which have also
damaged larger ones. Difficult to estimate age bones owing to activities
of crabs but am quite certain they are not less than four years old and
probably much older.
Doctor Hoodless later
concurred:
All
these bones are very weather-beaten and have been exposed to the open
air for a considerable time. Except in one or two small areas all traces
of muscular attachments and the various ridges and prominences have been
obliterated.
And
another colonial doctor who saw the bones, Dr. Lindsey Isaac, was of the opinion
that the “bones
have been in sheltered position for upwards of 20 years and possibly much longer.”
There is nothing
in their backgrounds to suggest that any of these men had experience in
assessing the age of bones found on Pacific islands. How accurate were
their judgments? Do coconut crabs (Birgus latro) really remove
bones? If so, how long does it typically take them to reduce a human skeleton
to the condition of the one found by Gallagher? Clearly some experimentation
was called for.
Above, a strawberry land hermit crab. TIGHAR photo by R. Gillespie.
Right, coconut crab, mid-sized; photo courtesy Walt Holm.
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Birgus
latro, the Coconut or Robber crab, is the world’s largest land
crab and is now considered an endangered species. We’ve seen adults
on Nikumaroro that are easily 18 inches across the back. It is believed
that individuals can live up to 60 years or longer – no one really knows.
The large adults tend to be elusive. The much more numerous strawberry
land hermit crabs, coenobita perlatus, are everywhere. |
The team’s dedication
to scientific inquiry did not extend to sacrificing one of our expedition
members so we had to find a substitute for a human body. The preferred
stand-in for such experiments is a pig because pigs are hairless omnivores
with roughly the same body mass and bone size as humans. Our plan was
for Dr. Burns to procure a suitable porker in American Samoa and our ever-gracious
hosts aboard our chartered expedition vessel, Nai’a, had even constructed
a cage for the purpose of transporting the subject of the experiment to
Nikumaroro. Unfortunately for TIGHAR (but fortunately for Porky) negotiations
for the purchase of the pig broke down when the patriarch of the Samoan
family learned that the animal would not be eaten by people but by crabs.
Such a fate was deemed unsuitable and the deal was off.
Plan B was less
satisfactory but more politically correct. A shoulder of lamb from the
butcher shop would have to do. On August 29, 2001 Dr. Burns laid out the
lamb shoulder at the foot of a coconut palm about fifty feet back in the
treeline from the beach and a couple hundred yards south of the landing
where we came ashore everyday. The idea was to pick a spot that was convenient
for monitoring but far enough away so as not to be influenced by the team’s
other activities. The photos below show the progression; click on each
picture to open a much larger version in a new window.
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August 29 – Day 1
Fresh meat.
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August 31 – Day 3
Attention from several hermit crabs and one purple “teenager”
(just to the right of the lamb shoulder) who is almost ready to
go without his shell.
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September 1 – Day 4
Feeding frenzy. The teenager doesn’t seem to have moved since yesterday.
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September 2 – Day 5
The flesh is gone but the ribs and the limb (shoulder blade and
leg bones) are still attached to each other by ligaments.
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September 3– Day 6
The ligaments have been eaten away exposing bare bone.
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September 4 – Day 7
One week. The bones begin to move.
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September 6 – Day 9
The joints between individual bones are being attacked and the limb
is becoming disarticulated (disconnected).
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September 10 – Day 13
In less than two weeks everything is gone.
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The lamb shoulder
experiment, rudimentary as it was, produced some surprising results and
raised some important questions.
- No adult crabs
were ever seen at the site. It appears that the devouring of the meat
and the disarticulation and removal of the bones was carried out entirely
by hermit crabs and young coconut crabs, but we do not know this for
sure. It’s not that the adults outgrow their taste for meat. We’ve seen
a big adult coconut crab dining on a dead rat that he had hauled high
up onto a tree limb leopard-style (yes, coconut crabs are great tree
climbers). But the adult coconut crabs are definitely more reclusive
than juveniles and hermit crabs. They may be appearing only under cover
of night – a question that could be answered by a nighttime video during
the next experiment.
- In most environments
the first-on-the-scene scavengers are blowflies but on Nikumaroro the
hermit crabs beat them to it and so completely cover the carcass that
the flies have almost nowhere to land.
- Something on the
island can and does go off with bones of the size of those in the lamb
shoulder. We suspect that it was the young coconut crabs but we did
not actually see them do it. We’ve seen them carry off smaller (pork
chop) bones but we’ve also seen a dead fish completely skeletonized
by tiny hermit crabs without a bone disturbed. The coconut crabs weren’t
interested. Do they not like fish? One does not usually think of crabs
as picky eaters.
Interesting
as the lamb shoulder experiment was, it doesn’t tell us how long it takes for
a human body to reach the state of skeletal scattering as the one found in
1940. The lamb shoulder was only about a tenth of a human’s weight and was
not protected by a layer of skin, nor were hair, teeth, internal organs, large
amounts of blood and other fluids present. (Expedition members who slept on
the island can attest, however, that all kinds of crabs have no difficulty,
and are not shy about, perforating the human epidermal layer.) What is clearly
needed is the full-fledged pig experiment, monitored by videocamera, with infrared
illumination at night.
The
results of the preliminary experiment suggest that the island’s reductive
environment acts far more rapidly than the British colonial officials
imagined. Indeed, the major accelerating factor appears to be the presence
of a large population of crabs. Further research
may establish that the castaway whose bones were found on Nikumaroro had
almost certainly been dead a matter of months, not years. If so, the
implications are disturbing. The island was continuously inhabited from
December 1, 1938. The skull was found in late April 1940 – nearly a
year and a half later. Was the castaway alive after the island was inhabited
but so mentally incapacitated as to avoid contact with strangers? Such
a reaction to prolonged isolation is not unheard of.
As always, more
research is needed. The full decomposition experiment is one of the tasks
planned for the Niku V expedition.
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