Natural history is a cornerstone of both theoretical and applied ecology, and provides the context for comparative and experimental studies. I studied the natural history of the Plains Garter Snake (Thamnophis radix) near the northern limit of its range in Miquelon Lake Provincial Park. Alberta, Canada. As is typical of garter snakes, T. radix at Miquelon were sexually dimorphic as adults - females grew faster, reached larger sizes and had relatively shorter tails than males. Mating occurred in spring and females gave birth in August; litter size ranged from 8-50 and was correlated with size of female. These snakes were generalist predators, but fed mainly on anurans when small, adding mammals and other prey as they grew. Despite sexual size dimorphism, I found no difference in diet between adult males and females. Feeding frequency was low overall (22%). especially in gravid females. In summer, snakes were found mainly near cover on south-facing field edges or in marshes, but not in forests, and moved relatively little. However, movement distances increased in fall as snakes sought hibernating sites. Snakes hibernated for up to eight months, either individually or in pairs, in rodent burrows. This study also revealed the importance of radiotelemetry when studying movements of small, secretive animals, as there were significant differences between the results obtained through opportunistic captures versus telemetry: habitat descriptions from opportunistic captures therefore were biased, although they still captured some elements of microhabitat use by T. radix. The data from this study will be important for comparative studies of the ecology of garter snakes and for the management of this species on the human-altered landscape surrounding Miquelon Lake.