Bonefield Dynamics
Measuring the Disarticulation and Dispersion of Skeletal Megacarcasses Overtime
Though scavengers play an important role in initial carcass break-down and nutrient redistribution, elephant bones can last for years. However, the position and distribution of the bones change over time, likely as a function of opportunistic scavenging and elephant density. Some larger carnivores like lions and in particular spotted hyenas drag bones as they gnaw them over the years. This probably means that skeletons found in areas of higher hyena density are more likely to be distributed further away from the site of death or crunched to pieces by powerful jaws.
However, scavengers aren’t the only large mammals that move elephant bones. Though some herbivores, like giraffes and kudu, may practice osteophagy (meaning they occasionally consume and move smaller bones), it is the behavior of other elephants that likely plays a significant role in skeletal disarticulation. Elephants have a fascination with the bones of other elephants, especially (it appears), the skulls, jaws, and tusks of their brethren. So, like hyena density, higher elephant density likely means more skeletal dispersion, though certainly less bone crunching.
Thus, our question is: What are the drivers of megacarcass skeletal dispersal through time?
We hypothesize that: The disarticulation of megacarcass skeletons and dispersal of the bones are governed by some combination of time since death, spotted hyena density, and elephant density.
In order to test our hypothesis, we mapped 37 different skeletonized megacarcasses throughout the park each with varying elephant and scavenger densities. To map these sites, upon arrival we marked the center of the carcass or “gravesoil,” and ran a 15-meter tape north, followed by a second tape south, then a third and fourth tape east and west. Next, using a 0.25meter quadrat, we walked the length of each line. Any bone that intercepted our path we weighed, identified (if possible), and recorded distance from the center of the gravesoil, direction (N, S, E, W), and physical damage, then returned it to its original location. Afterwards, we ran secondary tapes northeast, northwest, southeast, and southwest repeating the same methodology.
We are now in the process of analyzing our preliminary data. So far, we have found that sites vary widely in terms of total bone mass and relative dispersion. For example, some sites we visited have little to no bones, while others still contain a great deal. In some sites the bones are widely distributed away from the impact site, while others still have bones closely grouped together. Though we are still digging into what may be causing such patterns, we have much more to do in the field.
In the near future, we will return to “re-map” each of our 37 sites to see how much the bones have been moved in our absence. We will also map new sites in other areas of the park and continue our data analysis.