Snakes on a Plain: Spring emergence of the plains garter snake in Alberta.
By Kyle Welsh
In early May, I went to survey one of my salamander study ponds in Beaver Hills. While circling the pond and counting fresh gopher mounds, I noticed that the grass was rustling when the wind stopped. It was a distinctive sound only created by the continuous movement of a legless animal.
I looked up to see the signature bright orange stripe on the culprit, slithering towards a rosebush. “Garter snake!”, I hollered to my coworker on the other side of the pond. As I got closer, I noticed something odd about this snake. It appeared to move in multiple directions and I couldn’t quite find the tail end. “Two garters, wait, three, no…more…a ball!” I shouted as it hit me what I was seeing. Many snakes began to move towards the safety of nearby mammal burrows. We counted seventeen heads, plus several tails disappearing into the grass. There were likely other individuals that remained still and camouflaged.
In Canada, garter snakes (Thamnophis radix) are notorious for congregating in large breeding balls outside of hibernacula (large snake dens) in the spring. The one we saw was relatively small.
The ball strategy
Garter snakes gather into a giant snake ball for two reasons. First, it is warmer for them. Second, this is how they breed. When a female leaves the den, she is swarmed by eager males that want to breed. The first male to slither out of the den typically has the best chance of being first to the female. Much like the old proverb — the early bird gets the worm.
A strategy employed by late arriving males is to produce a chemical cue similar to that of a female. Other males are then confused and attempt to mate with the imposter. In doing so, the late arriving male still has a chance to get warm.
As ectotherms, snakes rely on their surroundings to raise their body temperatures. Because of this, it might seem surprising to see snakes active on days when the air temperature is quite cool, like this day in early May. However, ground temperature often greatly exceeds air temperature in the sunlight, and snakes are experts at raising their body temperature above ground temperature. They do this by finding suitable microhabitats where they can maximize sun exposure and minimize wind exposure. In the northern hemisphere, south facing slopes and hills are ideal. This particular hibernaculum in the Beaver Hills was exactly where it should have been, on a south-facing hillside.
A little help from the mammals
The hill was also pocked with small mammal burrows, into which the snakes retreated when we approached. Snakes, and other animals, can use these burrow systems as winter refuges, or hibernacula, to move below the frost line during winter. As the snow melts and the spring sun warms the ground, the snakes follow the increasing temperatures upward towards the surface. With the onset of cooler temperatures in the fall, they will return to their hibernaculum, where the ground temperature will slowly drop through the winter, driving them deeper underground.
The plains garter
The species we saw is the plains garter snake (Thamnophis radix). It is one of three garter snakes in Alberta and is a grassland specialist that prefers open prairies, where it hunts frogs and other small animals in wetlands and sloughs. Their orange stripe blends amazingly well into dry grass and cattails. The stripe also causes potential predators difficulty in estimating the speed of the fleeing snake, giving the snake a better chance of escaping. The plains garter snake occurs from central Alberta south through Texas. Throughout its range, this species can have a variable pattern, but is typically defined by a vibrant orange dorsal stripe against either a solid background of black or a checkered pattern over an olive or grey background. They also have a cream-coloured stripe running along each side of the body. The belly is a pale blue.
You may get the plains garter snake confused with Alberta’s other two native garters, the red-sided garter and the wandering garter, both of which are also striped.
The red-sided garter
The red-sided garter snake has a pale dorsal stripe over a black background that is interspersed with red side blotches. In central Alberta, this snake prefers wooded habitat and is more common to the west and north of Edmonton, while the plains garter snake is more common to the east.
The wandering garter
The wandering garter snake can be distinguished by a light gray background colour with black spots. The dorsal stripe is typically yellow. This species’ distribution overlaps considerably with the plains garter but is more common in southern Alberta, where it inhabits dry river valleys.
Where to find them
All three species are semi-aquatic and can be found in and around wetlands. To find the plains garter snake in the early spring and late fall, search exposed south-facing hillsides in fields and natural grasslands. In the summer, walk the edges of prairie and farm wetlands and you might see it hunting frogs. They will also bask on pavement in the morning and evening because it heats quickly and retains heat longer than many natural substrates. Be mindful when driving and try to avoid steam-rolling sun-bathing snakes.
Remember that if you see large number of garter snakes together, you are likely near a hibernaculum! Tread lightly and be sure to report your sightings to the Alberta Volunteer Amphibian Monitoring Program (AVAMP), which is on the Alberta Conservation Association (ACA) website. This will allow us to better understand the distribution and status of our snakes. For more information, go to www.ab-conservation.com or call 1-877-777-3764, or read Snakes of Alberta brochure.
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