This high death rate in the crossing made me wonder what to compare it to. I am more of a biologist than a historian so the fate of migratory birds and butterflies in their epic seasonal journeys seemed a good comparison.
The Michigan Dept of Natural Resources says:
Migration accounts for the majority of annual adult mortality in land birds (Sillett and Holmes 2002). This biannual journey is the most energetically expensive process in a bird's life.
All this means is that death on one of the migratory trips is likely, not that any single one is especially dangerous. I am not sure how to learn more and this is not really a biology blog ... too bad about that, by the way.
I don't think the picture below depicts a battle in Roman territory between the Romans and Carthaginians, but maybe it does depict a battle in Carthage.