Posted by: Anne Murray | March 20, 2015

Snakes show richness of our marsh habitat

The 500 hibernating garter snakes unexpectedly found during Boundary Bay dyke repairs at Beach Grove have attracted a lot of attention. When the snakes were disturbed and began to wake up, the decision was made to take them to Burnaby’s Wildlife Rescue Association (WRA). After being cooled down, the snakes were stored in buckets with damp sawdust. They will be kept in hibernation until their den site is restored and temperatures become warm enough to release them.

I asked herpetologist Professor Patrick Gregory of the University of Victoria about the snakes, which he identified from photographs as western terrestrial garter snakes (Thamnophis elegans), also known as western garter snakes, a species widely-distributed in western Canada. He explained that garter snakes are very variable in colour and size, so can be confusing for even experienced naturalists to identify. Typically, the western garter is greyish-brown with three paler-coloured stripes down its back. The stripes are broken by two rows of alternating, dark-coloured blotches, the top row of which invades the mid-dorsal stripe, giving it a variably wavy appearance. Yolanda Brooks at WRA told me that the snakes are different sizes. This is to be expected as females are larger than males, and snakes keep growing throughout their lives, with the rate of growth slowing with age.
Western garter snakes are common in Fraser marshes, where they readily enter water, despite their “terrestrial” name. They consume a varied diet of slugs, earthworms, fish, frogs, nestling birds, and small mammals, and have a primitive constricting ability, sometimes coiling their bodies around mammal prey while biting them. Their saliva may be mildly poisonous. Live young are born between July and September and in fall the snakes cool and lower their metabolic rate, before entering a den (hibernaculum) for the winter. The Boundary Bay hibernaculum is much larger than average for our region, but in other areas of North America, winter dens of hundreds or thousands of garter snakes have been found.

Other garter snake species are also found in our area. Common garter snakes may have bold black and yellow dorsal stripes, but like the western garter snake, they can vary greatly in colour and size. This wide-spread species occurs in a diversity of habitats from wetlands to hillsides. Another species, the northwestern garter snake often has a red dorsal stripe. It is less likely to enter water than the other two species, but will roam on beaches, grass margins of dykes, and woodland edges.

The very large congregation of western garter snakes on Boundary Bay is an indication of the richness of our local marsh habitat. Snakes are a well-adapted, essential component of the delta environment. It is most unfortunate that they were disturbed, and moving them was a very risky strategy, only suitable for an emergency situation. Hopefully their den can be reconstructed so that the snakes can be safely returned, and monitoring will be done by the Province to ensure the population survives.

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