Cervid Breakage Patterns in Western Montana

Sexual weapons are expected to withstand intense combat as weapon failure can directly impact an individual's reproductive success. Most weapons are permanent and a broken weapon costs that animal for the rest of its life. However, a few species regrow their weapons. The consequences of structural failure are lower in these animals, and they may invest less in their production as a result—leading to increased rates of breakage in the wild. Cervids (true deer) regenerate antlers each year, yet their rates of weapon failure remain unclear. In our study, we recorded breakage rates, antler point symmetry, harvest location, and age in Rocky Mountain elk (Cervus canadensis), mule deer (Odocoileus hemionus), and whitetail deer (Odocoileus virginianus). In over 509 males, we found differences in antler breakage across species with elk breaking significantly more (33%, 39/118), than mule (11%, 16/144) and whitetail deer (8.5%, 21/247). All of these rates were much higher than those typical of species with permanent weapons (1-3%). We found adults and asymmetrical males experienced the highest breakage, and males harvested near Darby, MT experienced slightly higher breakage than Bonner, MT. Our findings suggest antler investment is variable and may be linked to mechanical constraints or differences in behavioral strategies. Elk engage in non-contact signaling behaviors, like bugling and parallel and lateral walking, while mule and whitetail deer rely more on physical combat and may maintain stronger tools. Our study highlights the intersection of biomechanics, behavioral ecology, and evolutionary trade-offs in sexually selected traits across cervid species.