Thanks to awesome shows like “Matlock” (does anyone remember this show?), “Law and Order”, and “CSI” we all know the routine that police investigators follow when examining a crime scene. Find the victims, gain personal/demographic information, carefully sweep the crime scene for clues left by the perp, run evidence through fancy glowing machines in dimly lit club-esque police laboratories, then nab that killer. Easy enough, huh?
Honestly, investigating wildlife scenes is almost exactly like that…we don’t actually catch the animal that killed the other animal.
Our purpose investigating skeletons in the Okavango Delta was to determine what happened to animals from the time that they died until we arrived at that scene. And every skeleton we find, we will revisit on every trip to see how the bones may have changed over time.
First, after the death, what happens? There have been great studies where scientists watch a dead animal bloat as their insides fill with the gas of the bacteria that are decomposing the body from the inside out. If left unharmed by scavengers, the body will eventually rupture (no, I will not show a picture), and trust me, you don’t want to be near a body that does…it really stinks!!
Most often scavengers find the carcass and begin pulling meat away. Different scavengers feed differently, and most all of the skeletons that we find are scattered over large areas, hundreds of square meters. Smaller animals are consumed in one sitting by a single animal or one group so remains may not be as spread.
The bite marks left on the bones tell us who was eating what parts of the skeleton. Lions, hyenas, and vultures all leave very specific breaks and scratches on the bones because of feeding styles and the tools they have in their mouths.
So we have a body, we have the weapons of destruction, what next?
Time of death…
this can be trickier to determine. With a fresh carcass it is not that difficult, but the further away from the time of death the larger our error becomes. The easiest carcass we found was a leopard tortoise that died the previous night. We know this because one day the shell was not there on our drive, the next day it was. Yet, as years go by more and more evidence is destroyed, but that destruction can be a great clue. See, bones crack when exposed to the sun, and the pattern of cracking estimates the time of exposure. So we can determine if a skeleton was laid down up to 15 years prior!!
The killer. Sometimes we know what killed an animal because our guides saw it happen and can tell us. Or there are clues such the placement and size of carcasses that tell us leopards versus lions were the culprit. But a lot of times we can’t be sure. Once multiple animals begin feeding on a carcass bones get scattered and bites overlay one another. Still we try our best to determine patterns of predator behavior. Changes to the way predators feed can be wonderful indicators of ecosystem health.
Finally, game trails, or animal highways, can be a terrible disrupter to bone sites. As animals walk through a bone site they kick bones around, break them into pieces, or push them into mud. All around causing us grief. It was interesting though to see so many carcasses along game trails. Predator killing behavior? We need more data.
Lots of other information can be obtained from bone sites to help us understand the lives of the animals, including DNA sequences, stable isotopes revealing diet and travel of the animal, and amino acid decay to help time death. We hope to pursue many of these in the future on our quest to breath new life into old bones.