Gartersnake Tunnels in Manitoba

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Snake Tunnels in Manitoba
Narcisse is located in Manitoba's Interlake region where the landscape is predominantly Karst with large areas of marshland. This provides habitat for the Red-sided Gartersnake (Thamnophis sirtalis parietalis)a subspecies of the Common Gartersnake . The Red-sided Gartersnake is fairly common and, formerly, up to 100,000 individuals were provided annually to the science and pet trade. These snakes were easily picked from the den areas where they hibernate en masse each winter. Dens are located in sinkholes in limestone which must extend below the frost line while remaining above the water table for the snakes to survive the winter. With such requirements these sites are often scattered causing snakes to concentrate in numbers sometimes exceeding 70,000 individuals.

The season for snake picking has been closed since the 1980's and a den site is now advertised for viewing by the public. Research has been ongoing at this site since the late 1970's and, in recent years, researchers have been focusing on the problem of migrating snakes being killed as they cross a major highway (Highway 4) which passes within a few hundred meters west of the den area.

In the spring, snakes are eager to get to feeding areas on the opposite side of the highway as the denning site. They typically cross the road quickly and a few, approximately 1000, are hit by vehicles each year. In the fall, the snakes are in less of a hurry and loiter on the warm road surface where they are killed by the thousands. In the fall the snakes tend to move in several smaller waves before undergoing a major movement over a short span sometime in September. Unfortunately they are not necessarily inclined to remain around the den sites in cooler weather and may attempt to move east to west back towards their summering grounds. In fact, individual snakes may attempt to cross the highway multiple times before settling in the dens as winter approaches.

Students who have been counting snakes estimated that 10,000 snakes are killed each fall. Other, smaller, dens are located along this highway and the width of the migratory corridor varies from 1.5 to 2.5 km depending upon the number of snakes involved.

In attempt to reduce the numbers of snakes killed on the highway since the den areas were identified for public viewing researchers have erected road signs, put up drift fences leading to an existing culvert and to traps and manually transported animals across the road. In 1999 about 9,000 snakes were known to pass through the culvert near the north end of the area.

During the summer of 2000 Manitoba Hydro provided a machine to push culverts under the roadway to provide more opportunities for the animals to cross the area safely. Two such culverts were installed in June and two more were installed in the fall. Monitoring has been ongoing since students and volunteers put up drift fencing earlier in the year 2000. These new culverts cost merely a few thousand dollars to build, whereas a more traditional culvert may cost upwards of $25,000.

Bright road signs with characterized snakes warns motorists of the presence of these animals on the road. No official speed reduction has been posted but it is hoped that with slower speeds the snakes will have more reaction time. Slowing down to allow moving snakes to pass is a good idea, however, if come too close with the vehicle the snakes tend to curl up when they feel vibration. The surface of the highway is light in color making the dark garter snakes readily visible at slower speeds. However, at any given time during peak movements their may be hundreds of snakes on the road along a stretch of highway spanning 2 kilometres. Swerving around snakes is possible but caution should be exercised along this busy highway. If you have time it is worthwhile to pull over and get out to enjoy the spectacle of hundreds or possibly even thousands of migrating snakes!

There is a local snake mortality advisory group with representation from Manitoba Conservation, Manitoba Highways Department, University of Oregon at Corvallis and Manitoba Hydro. For direct information on the interpretation and for information from people working directly on the project, call Dave Roberts at (204) 642-6078 or email him. A snake plan was produced in the late 1980's related to the season closure and some den sites were identified in a report from the 1970's and there are publications on the work in this area.

Also in Manitoba there has been some recent pressure to install tunnels for Leopard Frogs in Hecla Island Provincial Park but there as been no action as yet. Tiger salamanders can also be a hazard there during fall migration but that is only for a day or so.