A Gnawing Question: How Do Caribou and Other Arctic Mammals Exploit Shared Bone Resources?

Bones of dead animals are consumed by many species, yet the partitioning of this resource, and the associated ecological and evolutionary implications, remains poorly understood. Using bone modification features found on shed female caribou (Rangifer tarandus) antlers and skeletal bones lying on caribou calving grounds of the Arctic National Wildlife Refuge (Alaska), we evaluated resource partitioning by co-occurring ungulates, carnivorans, and rodents. We found that 86.4% of shed antlers were modified by animals and that caribou were the dominant modifiers (99%); rodent (3.5%) and carnivoran (0%) modifications were rarely observed. Conversely, 44.2% of skeletal bones showed modifications, most of which were attributable to carnivorans (91.9%), and only rarely to caribou (12.1%) and rodents (1%). Carnivoran preferences for skeletal bones over shed antlers are consistent with their proclivity for the bones of recently dead animals, which are rich in fats and associated soft tissues. Ubiquitous ingestion by caribou of their population's shed antlers indicates the importance of a rarely recognized nutrient resource during the calving and post-calving intervals and offers new insights into the biological benefits of female caribou antlers. Caribou are the only cervid for which females grow antlers. In migratory populations, females shed their antlers after reaching their calving grounds and within only days of birthing their young. Pervasive antler consumption by caribou suggests that synchroneity between birthing and antler shedding evinces the importance of nutrient (Ca, P) transport for supporting calf survival and that osteophagy may have contributed to the evolution and maintenance of antlers in female caribou, along with their peculiar shedding schedules. Antler accumulations may also contribute to calving ground fidelity by establishing a predictable mineral reservoir in nutrient-poor settings.