Every year for a period of three weeks in the spring, dens like the ones around Narcisse, Manitoba, come alive with writhing mounds of red sided garter snakes. The non-poisonous snakes (Thamnophis sirtalis parietalis) have large dens or hibernacula in the water worn limestone rock.
Current estimates on the population run around 10,000 snakes for the site. This is down from the 1990s when estimates of 70,000 snakes denned there. The dramatic decline was due to a severe storm in 1999 that killed snakes during their migration. Since that tragedy, ways have been investigated to help maintain the existing population. As the snakes have to cross a highway, efforts were made to build a tunnel under the roadway to funnel the snakes. This effort has helped reduce the annual loss of snakes due to traffic fatalities by 90%. Where it was common in the past that 10,000 snakes a year would get run over, now the figures are closer to 1,000 snakes a year.
Females can usually be identified by their larger size. An adult female can reach lengths of 90cm (36 inches), while males reach a maximum of 75cm (30 inches). With high mortality though, the chances of a snake reaching old age is very slim. According to the Nature North Zine, chances are 1 in 5,000 of an adult snake surviving to its 12 year old maturity.
Where
Although there are other sites in Manitoba, the Narcisse pits are by far the most visited. The sites are found along highway 17 about 6 km north of the town of Narcisse, and are well marked with signs. Narcisse is 130 km north of Winnipeg (1 ½ hour drive).
When
The two times to view the snakes are either in the spring when they are mating, or in the fall when they return to their dens. In between the two times, the snakes are spending the summer in the local marshes.
Mating takes place for 2-3 weeks in the spring usually between the end of April and mid May. The return to the site in the fall usually occurs in September.
Why
Snakes are cold blooded and therefore cannot keep alive without hibernating somewhere warm in winter. The hibernaculum (den) provides just that, a place of warmth and protection.
In the spring, mating occurs with the males wrapping themselves around the larger female. Females don’t breed until they are three years old, and even then the first brood is only half a dozen snakes with 80% not surviving their first year. Adult females produce a brood of about 40 offspring, but will only breed every other year.
As competition to mate with the fertile female is very strong, multiple males will wrap themselves around her until a mating ball of snakes is formed. This is why visiting the den sites in the spring is so spectacular for the visitor, as the snakes are too preoccupied to bother about the close proximity of people.
As mentioned, Narcisse is not the only major den site for the red sided garter snake in Manitoba. Other places in the Interlake region also have hibernacula, although many have been destroyed by land development and ignorance over the importance of the snake in the health of an ecosystem.
References
Nature North.com article on garter snakes
Manitoba Conservation - Wildlife Management
Wikipedia.org article on Narcisse Snake Pits
 |
