Montane Carnivore Detection and Occupancy in the High Oregon Cascades

Marwa Mahmoud

doi:10.7273/000007415

The Cascade Range runs from southern British Columbia, Canada to northern California, USA and has been a stronghold of glacial refugia since the end of the Pleistocene. Yet, it is changing rapidly due to climate change. The section of the Cascades that lies in the state of Oregon (hereafter Oregon Cascades) provides high-elevation habitat for many carnivore species, including habitat specialists and generalists. While climate change may reshuffle carnivore communities in high-elevation areas, there is little known about the current distribution of the carnivore community at the highest-elevation areas of the Oregon Cascades. We completed a state-wide survey of carnivores, including bobcats (Lynx rufus), mountain lions (Puma concolor) coyotes (Canis latrans), Sierra Nevada red fox (Vulpes vulpes necator), and martens (Martes) in the highest-elevation area of Oregon, along the Cascade crest, using passive camera traps during the summers of 2023 and 2024. Within a subset of the Cascade crest, in the central Oregon Cascades we assessed the most effective methods of detection for the most elusive of the carnivore suite, the Sierra Nevada red fox. Finally, we assessed drivers of carnivore occupancy in the high-elevation landscape and forecasted projections of occupancy for the carnivore suite under intermediate and high emissions climate scenarios. In the central Oregon Cascades, we successfully and reliably detected Sierra Nevada red fox using on-trail cameras and scat surveys. We discovered that the Sierra Nevada red fox is likely to face challenges in the Oregon Cascades due to lack of available suitable habitat under intermediate and high emissions climate scenarios. In addition, we found that the occupancy of all carnivores in the high Oregon Cascades was driven by climate and disturbance, with habitat specialists (marten and Sierra Nevada red fox) exhibiting a positive relationship with snow water equivalent and a negative relationship with minimum temperature and habitat generalists (bobcat, coyote, mountain lion) exhibiting the opposite relationships. We identified relationships between habitat generalists and specialists, where some habitat generalists had positive relationships with human use (bobcat, mountain lion) and one habitat specialist had a negative relationship with human use (Sierra Nevada red fox). Under both climate scenarios, we found that all carnivores expanded further upslope in the high Oregon Cascades, with habitat generalists having more suitable habitat available for use and habitat specialists having less suitable habitat available for use. Based on our results, we suggest the best way to monitor the Sierra Nevada red fox is using on-trail cameras and scat surveys and we also suggest that the Three Sisters area of the Oregon Cascades may serve as climatic refugia for specialist species and therefore may require further protections (e.g., recreation management) to combat indirect and direct effects associated with climate change.

Montane Carnivore Detection and Occupancy in the High Oregon Cascades

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