Migration is the seasonal movement of an animal population in response to changing environmental conditions. While birds are best known for employing this survival strategy to cope with winter, many other forms of wildlife also engage in some form of relocation during autumn to deal with prolonged bouts of cold and an absence of food. Among the migratory reptiles in the Adirondacks is an abundant and widespread snake familiar to anyone that spends time outdoors – the garter snake.
As daylight wanes and the temperatures cool, garter snakes begin to travel to various sites that afford protection from the intense cold that settles over our mountainous region in winter. Typically, garter snakes rely on specific crevices that extend deep into a rocky outcropping situated on a south-facing slope. Also, garter snakes are known to utilize selected abandoned woodchuck, fox or skunk dens that exist deep enough into a hillside to get near or below the frost line.
The location of favored wintering sites is well known to older snakes and these individuals are first to make their way to such places during the early weeks of autumn. The garter snake is known to travel well over a mile to reach a preferred wintering site known as a “hibernacula”. It is believed that the older adults produce a distinct scent trail as they migrate to their wintering site. This unseen, yet detectable chemical path is then encountered by younger snakes as they move about their summer range, and is instinctively followed. (Like all snakes, the garter snake uses its forked tongue to draw odor molecules into its nasal passages for analysis by its exceptionally keen sense of smell.) After traveling to a specific hibernacula several years in a row, younger snakes eventually learn its location and begin to move toward it during the early autumn without the need of a scent trail.
By mid October, most of the garter snakes from one general area have arrived at the same place and begin to enter the chamber that will serve as their home for the next 5 to 6 months. By overwintering in a sizeable cluster, the individuals are better able to conserve the small amount of heat energy that their body dissipates during their dormant state. This improves the chances for survival should the frost line drop below normal and engulf their retreat.
Sharing the same wintering site also greatly reduces the amount of energy needed to locate a mate in spring when breeding occurs. The garter snake mates as soon as it emerges from its winter dormancy in early to mid April in the Adirondacks. This eliminates the need for individuals to expend a fair amount of time and energy in traveling about an area in search of a breeding partner in mid spring. In a northern climate where food can be in short supply in spring, spending virtually no additional energy in finding a mate is a great advantage for survival.
Individual snakes that were unable to find a communal wintering site, and simply descended into a deep hole in the ground in the area where they hunted throughout the summer, may be able to survive the cold alone if the frost line fails to develop very far below the surface. However, these snakes are not likely to easily find a mate upon emerging from their shelter in spring. Eventually, they may be able to track down a member of the opposite sex; however, the delay in breeding greatly jeopardizes their chances for a successful reproductive season.
For several weeks prior to entering the wintering chamber, a snake goes without eating. This allows all of the items it previously consumed to be completely broken down and absorbed into its system. As is the case with any cold-blooded creature, the lower the air temperature, the lower the animal’s body temperature and the slower the rate of all its life processes, including digestion. Should a snake happen to eat a large grasshopper, earthworm or small wood frog, just prior to the arrival of an unusually cold spell, the snake may become extremely lethargic and the contents of its stomach can fail to be processed in a timely manner. The longer it takes to process items in its stomach, the greater the chances that this dead material will start to decay, which could result in serious illness to the individual snake. As a means of allowing all of the material in their digestive system to be thoroughly processed and absorbed, snakes attempt to elevate their body temperature by basking in the sun. If several dozen garter snakes have already arrived at the hibernacula, this collection of reptiles will emerge from their sanctuary during warm and sunny weather and may be seen scattered near the entrance trying one last time to elevate their internal temperature.
Over the past several weeks, the Adirondacks have experienced some exceptionally warm and sunny weather. This has been great for hiking, camping, boating and for garter snakes to complete their migration to their local wintering site and prepare their body for their winter dormancy, properly known as brumation. Should you happen to encounter such a gathering of snakes, please do not disturb them, as these are beneficial creatures that are just trying to enjoy the sun as any sun lover would do here in the Adirondacks.
Photo of common garter snake by Mark A. Wilson (Department of Geology, The College of Wooster).