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Effectiveness of road mortality mitigation for Western Rattlesnakes (Crotalus oreganus) in Canada

Spruyt, Jade A.

Matson, Michelle

Larsen, Karl W.

Department of Natural Resource Sciences

Thompson Rivers University

Kamloops, British Columbia Canada

Bishop, Christine A.

Wildlife Research Division

Environment and Climate Change

Delta, British Columbia Canada

Reptiles, and especially species with life histories characterized by low reproductive rates and low adult mortality - like rattlesnakes - are extremely vulnerable to demographic consequences of road mortality. To combat road mortality and aid in habitat connectivity for vulnerable reptile species, mitigation measures are becoming increasingly common. However, in-depth analyses of their effectiveness on reptile species remain rare, both at the level of direct roadkill and the population persistence level. This study assesses the immediate impact of recently installed ecopassages and directional fencing on a Western Rattlesnake (Crotalus oreganus) population in British Columbia, Canada. Using road survey, traffic monitoring, and mark-recapture methods, we analyze trends in the roadkill rates and population size throughout the periods before, during, and after the mitigation was installed. Wildlife cameras in ecopassages allow us to quantify use by Western Rattlesnakes, and compare detection frequencies to other at-risk snake species in the area. Rattlesnake roadkill rates have decreased after mitigation installation, despite there being an increase in traffic. However, rattlesnakes were less likely to use ecopassages than colubrids in the same community, and population estimates do not indicate a clear trajectory of recovery. This study highlights the short-term effects of road mortality mitigation on this federally and provincially threatened species, and improves our understanding of how these animals adjust to the change in their environment. It also emphasizes that long-term monitoring is necessary in order to detect changes in ecopassage use and population size past the initial implementation phase.


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