The range of the Red-sided Garter Snake extends farther north than any other reptile in the western hemisphere. The extremely large population of red-sided garter snakes located in central Manitoba, Canada, is one of the most adaptable reptile populations existing under extreme climatic conditions that border on the subarctic. This population is able to survive winter temperatures that reach −40°C and snow cover that may be continuous for up to 9 mo. The extreme seasonal variations in this region present a major evolutionary force that dictates the characteristics of the population. Therefore it is not surprising that the entire life history of the red-sided garter snake in Manitoba, including reproduction, must be extremely seasonal in nature.
The red-sided garter snake has a very restricted period of activity each year that lasts approximately 3 mo. During this brief period of activity, individual snakes are widely dispersed throughout the summer habitat. Migration from the summer feeding areas to hibernacula begins in early to mid-August. It has been reported that individual snakes return to and hibernate in the same den during successive years (Gregory 1971). Migration, estimated to cover distances as great as 17.7 km, intensifies throughout August and early September; and by mid-September, several thousand to more than 8000 animals can be found around the entrance of the dens. Once they reach the hibernaculum, snakes remain in or near the mouth of the den, are active on clear sunny days, and retreat underground during cloudy weather and at night. Snakes finally disappear underground when the ambient daytime temperature remains below 0°C.
Although the cues responsible for spring emergence are not fully understood, snakes reappear on the surface in late April or early May. Due to the highly unpredictable nature of the weather during the breeding season, snakes must actively thermoregulate to increase their body temperature. However, Shine et al. (2000a) recently reported that warm snakes were not more successful in mating or avoiding predation than cooler snakes. In fact, courting snakes spent little time actively thermoregulating, and body temperatures were quite variable despite opportunities for more precise control. Garter snakes were found to cool rapidly, and any benefit of higher body temperatures would only be temporary. Because of the high cost of precise thermoregulation to snakes, the males must be concerned with courtship rather than taking the time to bask and increase body temperature.
In the spring, male red-sided garter snakes emerge essentially en masse from the dens and wait for females to emerge individually or in small groups over the next several weeks (Crews and Garstka 1982). Once mated, the female leaves for the summer feeding areas while males remain at or near the den until all courtship has ended before they disperse in late May or early June. From dispersal in late spring to the return migration in late summer, life history observations are minimal due to the difficulty of locating animals in their summer habitat. However, available data indicate that snakes spend the summer around marshes, and stomach contents collected during this period have contained primarily anurans .
After emergence, males compete for females and will copulate numerous times during the 4- to 6-wk courtship season. Upon emergence from low temperature dormancy, female red-sided garter snakes can be identified by courting males through the detection of a nonvolatile attractiveness pheromone that is present on the dorsum of the female. Noble (1937) reported that female common garter snakes (Thamnophis s. sirtalis) are sexually attractive upon emergence from winter dormancy and that this attractiveness appears to be associated with chemical cues exuding through the skin.
Vagvolgyi and Halpern suggest that males, in addition to recognizing females by a specific attractiveness pheromone, produce a male-identifying pheromone that communicates their male sex and acts as a signal to dissuade other males from courting the respective females. A male-identifying pheromone would have a beneficial role by reducing male-male courtship, which might limit their exposure to potential mates.