Predation risk for a particular prey species may be influenced by sympatry with another more common species, which can result in population declines for the less abundant species. Yet, predation risk models often neglect to account for the density of sympatric species. We used a novel case system from Southern California, where federally endangered Peninsular bighorn sheep (Ovis canadensis nelsoni) co-occur with southern mule deer (Odocoileus hemionus fuliginatus) to understand how sympatry between two prey species differing in abundance affects predation risk. We characterized landscape predation risk for bighorn and deer to discern how topography, habitat, forage, and prey density affect where pumas (Puma concolor) kill both species. The presence of the second ungulate species increased predation risk for both species, but had the greatest effect on bighorn, with risk strongly increasing with deer density. These findings confirmed how spatial overlap between low and high abundance prey species can lead to increased predation risk for lower density ungulate populations. They also support a more comprehensive understanding of risk interactions, which is critical to the success of ongoing bighorn recovery, and demonstrate that the density of sympatric species should be considered in population models and management planning.