Understanding inter- and intra-population variation in Western Rattlesnake migratory tactics in British Columbia

Howarth, Chloe R.

howarthc17@mytru.ca

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

Migration is a phenomenon central to many animals' ecology, allowing individuals to respond to changes in resource availability and exploit habitats favourable for critical life-history processes. Yet, migratory behaviour is not always ubiquitous within populations: multiple tactics can exist, often related to age class, sex, or reproductive condition. For Western Rattlesnakes (Crotalus oreganus) at the northernmost extent of their range (British Columbia - BC), seasonal migrations between hibernacula and summer ranges provide access to essential food resources and mates. Multiple studies by our group has revealed immense variation in migratory behaviour and habitat use within and between populations, although the reasons for this variation remain unclear. I will be providing an overview of the current state of knowledge in the field of Western Rattlesnake movement ecology in BC, and I will highlight how our ongoing research aims to address gaps in current understanding. Specifically, using radio-telemetry data from multiple sites collected over 15 years, we are quantifying clear and unique migratory tactics and considering whether these tactics appear linked to site, landscape characteristics, and coarse-scale habitat features across BC. Further, we are considering whether ontogenic shifts in migratory strategies (seen in many other species) occur in our study populations. While several studies have investigated the movements of adult rattlesnakes and a handful has explored neonatal den location behaviour, little information exists regarding the ontogeny of rattlesnake migration behaviour; in general, juveniles are a grossly understudied rattlesnake demographic. We used radio-telemetry to assess juvenile movement and collected habitat data along their movement pathways. Our preliminary results indicate that the variation seen in adult rattlesnake migration also is present in juveniles, and that these younger animals select habitat with high rock and woody-debris cover at multiple spatial scales. This work is providing vital information for developing conservation strategies that recognize varying types of migratory behaviour in a threatened species.