In all, Boarman locates 28 shells this day under various nests and posts. The shells all feature large holes in the middle where the raven has pecked through to get at the tortoise. It wasn't until the late 1970s, when in-depth studies of desert tortoises began, that biologists discovered tortoise shells like these in the Mojave. Under one Southern California raven nest, scientists found 250 shells during a two-year period. Most raven predation of tortoises takes place in spring when raven chicks hatch and raven pairs must feed their hungry, noisy broods.
Spring is also the time when tortoise juveniles are most active.
Though this predator-prey relationship is not new, prior to the advent of towns, roads, landfills, irrigation and farms in the desert, raven numbers had been so low that they were not a significant problem. The raven is one of the most widespread birds in the world. Ravens gulp down their food in chunks, and then, like owls, cough up a pellet of all the indigestibles. Boarman displays a raven pellet that contains some aluminum foil, the shell from a beetle, bones from a rodent and a tortoise leg. Humans do not generally regard ravens as beautiful.