How snakes overwinter
Posted onJanuary 12, 2023by|,
There are over 3000 species of snakes globally that have a variety of habitat and resource requirements. Although needs vary across regions, all snake species share a few recurring necessities in their habitat range. Within their habitat range, snakes need access to food, water, shelter, and a safe place for gravid females to give birth. As we bundle up for the cold winter ahead, an extra requirement for snakes in cold climates becomes apparent; a place that is suitable to spend the winter.
Snakes are ectothermic and need external temperature regulation to survive. This means that the habitat necessities are different for snakes living in hot and cold climates. In colder climates like Canada, they must go through brumation in the winter months. Brumation is a very similar process to hibernation, but it is used by ectotherms rather than endotherms. Similar to hibernation, snakes slow their breathing and metabolic rates while in brumation, but unlike in hibernation, they are not in a state of deep sleep. When ectotherms brumate they can still move around, and on particularly warm winter days they are known to leave their hibernacula to bask in the sun.
An eastern gartersnake (Thamnophis sirtalis) brumating in a WPC made artificial hibernaculum.
A hibernaculum is a place where a snake overwinters. This is usually a natural feature of a landscape such as another animal’s burrow, rock pile, or dead tree. It can also be man-made like a building foundation, or an old well. The hibernacula must meet specific characteristics to keep a snake safe over the cold winter months. When a snake is brumating below ground the space must maintain a consistent temperature above 0°C so it does not freeze. The den should be below the frost line, which could mean descending over 1 meter below ground. A well-insulated hibernaculum makes it easier for the snakes to maintain a low metabolic rate.
While the den keeps the snake at the righ temperature, the metabolic rate is consistently lower, and they use less energy and can last longer in brumation. They do not need to eat while in brumation but they still need to consume water so there must be an accessible source. As water below the frost line remains liquid throughout the winter and typically maintains a steady temperature of 4-6°C, hibernacula in areas with a high water table can be less prone to sudden changes in temperatures. This consistent temperature can not only protect snakes from sudden cold or warm temperatures which could harm them, it also allows snakes to maintain a consistently lower metabolic rate. However, should a snake get trapped in a flooded hibernaculum, it could eventually drown without access to air.
Snakes in Canada generally brumate from late October to March or April. Some species of snakes prefer to brumate alone or in small numbers while other species do so in groups, possibly due to a limited availability of hibernation sites. It can also be beneficial to brumate in groups as it means that potential mates will be close by after emergence.
An eastern gartersnake (Thamnophis sirtalis) emerging from a possible hibernacula. Photo: Kathleen Woodhouse
If there are not enough safe places to wait out the winter many snakes will not survive the onset of cold temperatures. A lack of suitable hibernacula can limit a snake population. You can help! Artificial hibernacula (click link for more) can be made out of rocks, gravel, sand and wood, supplementing this critical habitat for snakes living in areas lacking enough natural hibernation sites. Providing snakes with safe and suitable hibernacula can be crucial for helping at-risk populations (click link for more).
Example of how an artifical hibernaculum could be made. Source: https://www.torontozoo.com/adoptapond/snakehibernacula.asp
In the spring as the outside temperature begins to get warmer, snakes will often emerge from their hibernacula to bask, but remain nearby in case the temperature begins to fall again. The snakes start to emerge and disperse from their hibernacula when temperatures consistently reach around 15°C, varying depending on the snake species and location. Very soon after they emerge from their hibernacula it’s the mating season! This means that the yearly cycle for the snake has begun again, and the population will soon be reinforced with new young snakes.
Harvey, D., & Weatherhead, P. (2006). Hibernation Site Selection by Eastern Massasauga Rattlesnakes (Sistrurus catenatus catenatus) near Their Northern Range Limit. Journal Of Herpetology, 40(1), 66-73. doi: 10.1670/89-05a.
Lang, J. (1967). Overwintering Three Species of Snakes in Northwestern Minnesota (Undergraduate). The University of North Dakota.
Markle, C., Moore, P., & Waddington, J. (2020). Temporal variability of overwintering conditions for a species-at-risk snake: Implications for climate change and habitat management. Global Ecology And Conservation, 22, e00923. doi: 10.1016/j.gecco.2020.e00923