Compensatory Microhabitat Selection by Northern Pacific Rattlesnakes (Crotalus oreganus oreganus) in a Cool and Wet Macroclimate

Northern Pacific Rattlesnakes (Crotalus oreganus oreganus) have a range that extends from southern California into British Columbia. This subspecies is common in relatively warm and arid regions, but also occurs in habitats that are neither warm nor arid. We hypothesized that the presence of suitable microhabitat conditions can compensate for a less suitable macroclimate, allowing C. o. oreganus to exist in less suitable regions. We developed environmental niche models for C. o. oreganus at two spatial scales: (1) northern California and western Oregon, and (2) the northern California coast. These models explored macroclimatic suitability of northern, coastal California relative to other regions within the range of C. o. oreganus. The models revealed that the three most northern and coastal counties of California have a significantly less suitable macroclimate relative to the rest of each study area. Next, we used paired resource selection functions to determine microhabitat differences between rocky outcrops used as hibernacula and outcrops that are unoccupied by rattlesnakes despite similarities. Our analysis indicated selection for outcrops with more deep crevices, less vegetative cover, and slopes facing due south (180 degrees from North). Additionally, we mapped landslides near hibernacula, which revealed that hibernacula commonly occurred within the head-scarps of landslides. We suggest that because landslide triggers (e.g., heavy rainfall and earthquakes) occur frequently along California's north coast, more rocky outcrops are created that are suitable as hibernacula. The relatively high abundance of these suitable outcrops compensates for the marginal macroclimate, allowing C. o. oreganus to occur in the region.