DO BITE MARKS ON ASSEMBLAGES OF CARIBOU CALF BONES RECORD DIFFERENTIAL PREDATION PRESSURE BY MAMMALIAN AND AVIAN PREDATORS?

Bite marks and other bone modifications provide physical records of predator- and scavenger-prey interactions. However, not all predation or scavenging events lead to bone modification or are preserved in bone assemblages. This is a particular concern for bones of smaller-bodied prey, which are more susceptible to destruction. To test the fidelity with which bone modification records known predator-prey dynamics for ungulate prey with bones that are fragile relative to the destructive potential of their predators, we evaluated carnivore modification on the bones of caribou (Rangifer tarandus) calves from the Arctic National Wildlife Refuge, AK. Calf bones provide an ideal system for evaluating the faithfulness of interactions recorded within bone assemblages because they are poorly mineralized and likely susceptible to modification during predation and scavenging. Calf bones were collected using standardized taphonomic surveys from 2010-2018. Each of the recovered calf bones (NISP = 435) was visually inspected for modification traces left by carnivores (mammalian and avian). We then compared the frequencies of observed mammalian and avian bone modification (summarized by MNI and NISP) to observed (1983-2001) carnivore activity on caribou calves from the same region. Biomonitoring data indicate that the dominate predator of caribou calves was golden eagles (Aquila chrysaetos: 37% of annual calf mortalities), followed by brown bears (Ursus arctos) and wolves (Canis lupus), which were responsible for a combined 24% of mortalities. Our assessments of bone modifications indicated that ~20% of calf MNI recorded modification by avian predators, ~30% by mammalian carnivores, and ~50% were unmodified. Thus, avian modifications on caribou calf bones were significantly underrepresented relative to expectations (P < 0.01) and mammalian carnivore modifications overrepresented. Discrepancies between observed calf predation and bone modification could be attributed to high incidence of mammalian scavenging, which are indistinguishable from predation-derived marks. While incidence of avian modification to calf bones suggests such predator-prey interactions are represented in some fossil archives, the proportional contributions of avian vs. mammalian carnivory is unlikely to be faithfully recorded.