35 Years on the Northern Frontier: Population Level Response of the Western Rattlesnake (Crotalus or

Atkins, Marcus

Environmental Science Program

Thompson Rivers University

Kamloops, British Columbia, Canada

atkinsm18@mytru.ca

Larsen, Karl W.

Department of Natural Resource Sciences Thompson Rivers University

Kamloops, British Columbia, Canada

klarsen@tru.ca

Periodic assessments on the status of wildlife populations rely on the best available science. However, long-term datasets that utilize historical, comparative data are limited. Robust historical comparisons allow for the quantification of long-term impacts and can help prevent a shifting baseline. This study represents the first comparison of long-term population changes of Western Rattlesnakes (Crotalus oreganus) in Canada. Temporal comparisons are being conducted through a rigorous mark-recapture study to compare and assess baseline demographic, morphometric, and female reproductive data with a detailed dataset from the 1980s. Since the historical data were collected, the study site has diverged into a ‘natural experiment’ of contrasting land-use patterns: half within the boundaries of a protected area and half within an active cattle ranch. Spatial comparisons via radio-telemetry and analysis of demographic data between sites aim to determine how long-term, divergent land management regimes influence population size and behaviour over time. Although preliminary, we are suspecting declines among the major denning populations since the last assessment, with the most severe declines appearing to be within the protected area. Preliminary data also suggests snakes occupying ranchlands are both longer (P = 0.034) and heavier (P = 0.055) than snakes within the protected area. This project is in the midst of its second field season.