When it comes to bright red garter snakes, the so-called “flame” garters from the Montreal area, bred in captivity now for many years, may be the first thing that comes to your mind. But bright red garter snakes are found elsewhere; I’ve heard stories of red garters from the Timmins, Ontario area — and a few years ago there were reports of red garters from northern Manitoba, near the zone of intergradation between Eastern (Thamnophis sirtalis sirtalis) and Red-sided Garter Snakes (T. s. parietalis). As far as I knew there were no implications in terms of new subspecies, just another example of the variability in pattern and colour you could get with Common Garter Snakes, especially Easterns.
A study on extreme colour morph variation in garter snake populations in northern Manitoba and Isle Royale, Michigan, has just been published in Copeia. The study found extreme red-colour variations in three of eight populations studied, plus melanistic snakes in several of the populations, and suggested that because of this variability of colour, “subspecies of T. sirtalis based on color are of questionable validity.” Which I take to mean that if red populations show up here and there all over the place, then relative reddishness is not grounds for declaring a local population a distinct subspecies. Whether this will have implications for western subspecies such as the Red-spotted (concinnus), California Red-sided (infernalis), Valley (fitchi) and even San Francisco (tetrataenia) remains to be seen, but that’s what I infer from that statement.
The Winnipeg Free Press reports on the study in lay terms.