Tanning turtles

The problem
NORTHERN MAP TURTLES (that’s Glyptemys geographica for those of you who like Latin) are found in northern states and southern Ontario and Quebec. They hibernate through the coldest parts of the year in communal groups on the floor of lakes and rivers. They don’t come up to breathe for the entire hibernation. Since they spend a lot of time in the sun during the summer, Map Turtles like areas that have fallen trees or other objects to bask on near large bodies of water. Basking sets their body temperature, but the more important question is just how energetically vital is sun-basking to these northern turtles?

The researcher
University of Ottawa professor Gabriel Blouin-Demers studies the physiological ecology of reptiles. He integrates laboratory experiments with field observations to better understand how phenotypes or biological traits—especially behavioural—are set by reptiles’ physiologies.
Blouin-Demers hopes that the research coming out of his laboratory can contribute to reptile conservation. Reptiles are in fact the most threatened vertebrates in Canada.

The project
The northern Map Turtles that Blouin-Demers studied were from Lake Opinicon (100 km south of Ottawa). He implanted thermometers into the abdomen of juvenile turtles to continuously monitor their body temperature for two years. Using their body temperature, Blouin-Demers can calculate the turtles’ metabolic rates to estimate how important thermoregulation is to the energy available for growth and reproduction.

The key
Blouin-Demers determined that basking has a huge impact on the energy budgets of northern Map Turtles. The turtles spend three-quarters of their day basking in the sun.
More importantly, he found that if northern Map Turtles don’t bask, their metabolic rate slows by as much as a third. This amounts to a huge loss in available energy for growth, reproduction, and everyday turtlely business. Despite the clear importance of basking, Blouin-Demers discovered that the turtles bask a little less than the theoretically expected optimal amount. Blouin-Demers speculates that this is because basking is a mutually exclusive behaviour: Turtles can’t multi-task while basking. They bask on land but do all their other important activities (like foraging and mating) in the water, so they must compromise.

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