Northern Pacific Rattlesnake, British Columbia, Canad

At the entrance to its winter hibernaculum in a rocky outcrop in British Columbia’s Boundary Region,
a Northern Pacific Rattlesnake soaks up the last rays of sun on the autumn equinox.

Life at these more northerly latitudes can understandably present some challenges for reptiles. As ectotherms, snakes are reliant on heat from the sun to maintain their preferred body temperature; unlike us endothermic humans, who are able to convert food into the energy necessary for thermoregulation. So, to make it through long, cold winters when the sun is either absent, or too weak to provide adequate warmth, snakes must seek refuge inside dens where their body temperature remains around 7°c for several months, despite outside temperatures plunging to -20°c or lower, just a few metres away. In early fall, they prepare for hibernation by gathering communally at these den entrances; usually in the form of deep fractures in large, rocky outcrops that hold the sun’s warmth throughout the winter. Here they bask, languid in their movements as they digest their last meals of the year. Soon the onset of poor weather sends them deeper into the den, where they’ll remain until April, by which point the cliff - serving as a big “heat battery” - has discharged most of its energy. By early spring however, ambient temperatures have increased enough to allow snakes to again venture into the grasslands to seek out a long-awaited meal.

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