Western Rattlesnake (Crotalus oreganus) spring migration in British Columbia: A comparative study of juveniles and adults

In many species the spatial ecology of early age classes can differ significantly from adults. Adult Western Rattlesnakes (Crotalus oreganus Holbrook, 1840) at the northern extent of their range undertake small-scale but important seasonal migrations between communal hibernacula and summer foraging and mating grounds. Mature snakes also show annual fidelity to their migratory paths, providing a useful system to examine the development of migratory behaviour. We examined and compared spring outbound migratory movements of juveniles and adults at a site in southern British Columbia, Canada, using radio-telemetry data collected between 2011 to 2016 (adult snakes) and 2021 (juvenile snakes). We found that compared to adult rattlesnakes, juveniles displayed similar directional orientation, direction of vertical migration, and path sinuosity, but initiated spring migrations later and exhibited shorter movements in terms of distances and rates. For example, juvenile straight-line migration distance (262 ±90 m) was significantly shorter than for adults (1069 ±134 m; P <0.001). We provide a starting point in attempting to understand an important question in migration – how individuals early on in their lives adopt different tactics – while contributing to our growing understanding of the complexity of patterns and variation in the movement ecology of a far-ranging snake.