Sunday, October 17, 2010

High Latitude Garter Snakes

The post on Garter Snakes in Newfoundland attracted much attention, so I investigated high latitude garter snakes a bit further. As far as I can see this news report is the first evidence of snakes from Newfoundland. But, in central and western Canada garter snakes have been known to reach relatively high latitudes, latitudes, higher than that report in Newfoundland.

Garter Snakes are quite cold tolerant and range farther north than any other North American snakes. They are also capable of submerged hibernation, a poorly studied behavior (Murphy 2010) and one that undoubtedly increases their survival at high latitudes.

John Richardson (1851) [in Bauer and Russell, 2001] appears to be the first to report garter snakes in central Saskatchewan, when he observed garter snakes at Serpent Lake. The earliest reference to garter snakes in Alberta appears to be Ǽmilius Simpson’s journal written in 1826. He was traveling on the North Saskatchewan River and passed the confluence with the Stone River at noon, he was at 53º45’34”N, 110º40’W and the temperature was 75ºF. The bank was limestone and clay, and he wrote, “…we passed great numbers of small striped Black & green snake swimming from the South to the North Bank of the River & strewed along the Sandy Beach on the North Shore, as if enjoying the powerful influence of the Sun, & it appeared that those crossing were leaving the cold of the Northern aspect to gain the more pleasing heat of the southern exposure.”

Bauer and Russell (2001) examined Simpson’s account and adjusted his co-ordinates, suggesting that they were actually, 53°45’15”N, 111°10’W and the area Simpson passed at noon is now known as Fort Island. Three species of garter snakes occur in Alberta: the Plains Garter Snake, Thamnophis radix, the Wandering Garter Snake, T elegans, and Red-sided Garter Snake, T sirtalis. The Wandering Garter Snake is restricted to the southwestern Albert in the Rocky Mountain and prairie biomes, but specimens are occasionally found much further north, and the species is often associated with rivers. All modern records from the vicinity of Fort Island are attributable to T radix, and most are from localities in Aspen Parkland or Prairie, with a few Plains Garter Snakes collected in the Boreal Forest Biome north of the North Saskatchewan River. Simpson’s color description describes both the Red-sided Garter Snake and the Plains Garter Snake and both species are associated with water and swimming behavior, T. sirtalis more so.

Larsen et al. (1993) studied this snake at Wood Buffalo National Park (59º49'N, 112º W) in the Northwest Territories, Canada. This is the highest known latitude for Thamnophis sirtalis. Thet found females rarely gave birth in 2 successive years. Female snakes matured at larger body sizes (570 mm) than snakes in Manitoba (527 mm), and they had smaller litter sizes than Manitoba females. The authors conclude that there is no single suite of life history traits for northern populations of garter snakes. The smallest gravid female they observed was 670 mm, but found a 570 mm female that had mated.

But are there garter snakes in Alaska? McDonald (2003) noted that the valleys of the Stikine River and Taku River (and perhaps Unuk River) could potentially allow Thamnophis access to the coast from the interior British Columbia, however, it remains unclear if snakes occur in these drainages. A preliminary search for garter snake records from major drainages that flow into coastal Alaska did not produce any evidence of their presence. McDonald reports that a resident of Telegraph Creek, BC, stated that he could not recall anyone ever seeing a snake in the area. The Common Garter Snake (Thamnophis sirtalis) has been reported north of Terrace, British Columbia, in the watersheds of the Nass and Skeena rivers, and along the eastern side of the province as far north as the Peace River District (Gregory and Campbell 1984). The Western Terrestrial Garter Snake (T. elegans) is found along the British Columbia coast, including Vancouver Island, as far north as the Skeena River Basin, and east of the Rockies as far north as the Peace River District (Gregory and Campbell 1984).

In eastern Canada the Maritime Garter Snake, Thamnophis sirtalis pallidulus, covers a considerable amount of geography. Bleakney (1959) redescribed the subspecies Thamnophis sirtalis pallidulus noting that its coloration was distinct over a large area and that it shows sexual dimorphism in ventral scale and subcaudal counts, commenting that T. s. pallidulus from Nova Scotia have 6 to 7 fewer ventral scales and 7 to 10 fewer subcaudal scales than T. s. sirtalis. And, he writes, “The subspecies [T. s. pallidulus] ranges throughout the Atlantic Provinces (exclusive of Newfoundland), westward into New Hampshire and thence northwestward to James Bay, and eastward again along the north shore of the Gulf of St. Lawerence.”

Barnes et al. (2006) examined the ecology and morphology of the population of the Maritime Garter Snake on Georges Island, Nova Scotia and marked 391 garter snakes, reported a male to female ratio of 0.8:1.0; and a population density for adult snakes of 120/ha. They found these snakes to be exceptionally docile, and the population contained melanistic individuals. Perhaps most remarkable they found female snakes reproductively active at a body length of 350 mm. This is quite small, Fitch (1965) reported that Kansas males mature at about 400 mm, and females mature at about 500 mm or 15 months of age. It seems likely that high latitude populations will grow more slowly and mature at smaller sizes and older ages due to abbreviated season of activity, but the studies done to date show a range of sizes at maturity for female snakes.

Gregory and Larsen (1993) studied geographic variation in litter size and neonate size in several populations of garter snakes (T. sirtalis) across Canada and found gravid females differed significantly in body size between the sites. Even after they corrected for inter-site differences in female body size, there were highly significant differences in litter size and neonate size. Populations with large litters tended to have small progeny, but they found only weak evidence of a "tradeoff" between neonate size and litter size within populations. Snakes from eastern Canada were relatively small at maturity and produced large litters of very small young, while those from western Canada were usually large and produced smaller litters (for a given body size) of larger young. 

 The map above shows the Newfoundland Record (red Triangle), the Wood Buffalo population (grey square), the approximate range of T. s. pallidulus (blue shading) and some high latitude locations for sirtalis on the west coast (black spheres).  

This is not an exhaustive compilation of high latitude Thamnophis. If you know of others leave a comment.

Barnes, S. M., C. M. Dubesky, and T. B. Herman. 2006. Ecology and morphology of Thamnophis sirtalis pallidulus (Maritime Garter Snakes) on Georges Island, Nova Scotia. Northeastern Naturalist 13(1):73-82.

Bauer, A. M. and A. P. Russell.  The First Record of Reptiles in Alberta: AEmilius Simpson's Journal of 1826 Herpetological Review 32(3):174-176

Bleakney, S. 1959. Thamnophis sirtalis sirtalis (Linnaeus) in eastern Canada, redescription of T. s. pallidula Allen. Copeia 1959(1):52-55.

Fitch, H. S. 1965. An ecological study of the garter snake, Thamnophis sirtalis. University of Kansas Publication, Museum of Natural History 15:493-564.

Gregory, P. and K. W. Larsen. 1993. Geographic variation in reproductive characters among Canadian populations of the common garter snake (Thamnophis sirtalis). Copeia 1993(4):946-958.

Larsen, K. W., P. T. Gregory, and R. Antoniak. 1993. Reproductive ecology of the common garter snake Thamnophis sirtalis at the Northern Limit of its range. American Midland Naturalist 129:336-345.

McDonald, S. O. 2003. Amphibians and Reptiles of Alaska, A Field Handbook.

Murphy, J. C. 2010. Secrets of the Snake Charmer, Snakes in the 21st Century. Bloomington: iUniverse. 420 pages.

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