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Tucked-In Turtles

How Western Painted Turtles survive the winter

This winter, did you feel like going into hibernation? We can deal with the cold by turning up the thermostat or putting on a sweater, but wild animals have to go to more extreme lengths to survive the chilly months. Over the winter, the Rufous hummingbird flies all the way to Mexico, while the Anna’s hummingbird stays here and adapts to the cooler temperatures. The Little Brown bat finds rock crevices or dry attics to sleep deeply all winter, while the Hoary bat flies down to southern California to find food. Barred owls stay warm in the cold with their fluffy down feathers, spending time in tree hollows to stay out of the rain and wind. Whether they migrate, hibernate, or just adapt, all animals have amazing and different ways to survive through the cold season.

The Western Painted turtle has an unusual and remarkable strategy for winter survival. These reptiles are found on the south-east side of Vancouver Island and throughout southern British Columbia, and are our only native turtle species here on the west coast. Similar to other reptiles, turtles cannot generate their own heat; this is known as cold-blooded or ectothermic. These animals rely on external heat from the sun to warm up their bodies to move their muscles to catch prey, run from danger, and digest food. When the temperature drops in winter, a turtle’s internal temperature, heartbeat and metabolism drops as well, bringing a major lifestyle change to these cold-blooded creatures. To survive the winter, reptiles must enter a hibernation-like state, called brumation. This slowed-down pace allows reptiles to survive winter without using stored body fat or losing weight.

In the fall, the adult turtles swim to the bottom of lakes and ponds and bury themselves in the mud. They have air-breathing lungs and must hold their breath below the surface, but the icy temperatures slow their bodies down so dramatically, they do not require the amount of oxygen they needed in the summer. Instead of relying on their lungs, turtles actually absorb oxygen through parts of the bodies that are flushed with blood vessels—in their neck and cloaca (their bum!). Oxygen enters into the bloodstream and keeps the turtle’s incredibly slow metabolism alive. Even if the water freezes over, there is already dissolved oxygen in the lake from aquatic plants and water currents.

Turtles are not the only animals that rely on dissolved oxygen in the water. Fish, insects and brumating frogs also live and breathe in the water all winter long. By the end of the season, especially if the water has frozen on the surface, oxygen levels can drop dramatically. For our turtle friends buried at the bottom, this can be particularly dangerous. Thankfully, turtles have one more trick up their shells to survive through the cold months. They can switch to an anaerobic metabolism, meaning they can survive without oxygen. Anaerobic metabolism uses solely carbohydrates for energy, rather than carbohydrates, fats and proteins as is used when oxygen is present. This turns the glucose, or sugars, in their bodies to lactic acid—essentially transforming their bodies into a giant muscle cramp. Similar to how people can take Tums to combat heartburn, turtles use the calcium from their shells to deal with the acid buildup in their bodies.

When the spring sun warms the waters and melts the ice, turtles very slowly and vulnerably emerge from their muddy beds to swim to the oxygen-rich surface. This can be a particularly dangerous time for turtles, as their slow bodies take time to recover from their full-body muscle cramp. They soon begin to feed on plant materials, fish and insects to regain their body strength for the warm weather ahead.

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Erica Van Dyk
Erica Van Dyk is a Program Naturalist at the Swan Lake Christmas Hill Nature Sanctuary and invites you to the Nature House to come check out the educational honey bee hive!

Family Summer Guide 2020

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