Though many species employ behaviors to mediate metabolic costs, it is difficult to identify the factors that influence these behaviors. This is especially true for the Pacific marten (Martes caurina), a small and cryptic carnivore associated with montane forests in the western United States. Martens have high energy requirements that necessitate bouts of rest to offset expenditures associated with foraging efforts. We hypothesized that microsites (e.g., subnivean chambers) may provide thermal refugia for martens during resting bouts. Further, we presumed that structurally complex vegetative stands, often associated with resting and foraging behaviors, would exhibit a higher thermal buffering capacity than simple or open stands. To evaluate the thermal properties of marten rest structures and habitat in Lassen National Forest, CA we used data loggers (HOBO Pendant, Onset Co.) to 1) quantify the thermal efficiency of resting microsites and 2) collect hourly temperature data among various environmental strata. In 2016, we deployed data loggers at 11 subnivean rest sites and 46 randomized points stratified by vegetative stand type (Complex, Simple/Thinned, and Open), elevation, and aspect.
Results/Conclusions
Temperature decreased at a slower rate inside subnivean microsites than at paired exposed sites (𝑥̅ 𝑖𝑛=22.2 minutes, 𝑥̅ 𝑒𝑥= 17.2 minutes, P=0.18) suggesting these structures exhibit some insulative properties. Preliminary data suggest that temperature fluctuates significantly less in complex forest stands than in simple or open stands (𝑥̅ Comp =9.5°C, 𝑥̅ Simp =12.2°C, 𝑥̅ Open=16.2°C, F=30.1, P=<0.0001); these complex stands accounted for the greatest proportion of marten resting and denning locations, and we believe martens may be selecting these stands in part because of their thermal buffering capacity. Our results emphasize the value of complex vegetation to metabolically limited species, and enrich our understanding of marten habitat use. In 2017, we will continue deploying loggers within subnivean chambers, and plan to expand our sampling scheme to include cavities in arboreal rest and den structures. We will also attempt to quantify the effect of temperature on spatiotemporal patterns of marten movements by pairing thermal data with GPS collar data. Through these efforts we hope to address a critical gap in knowledge of factors that influence rest and den structure selection and movement patterns, and highlight the physiological impacts of forest management and disturbance.