Thermoregulation of spotted turtles (Clemmys guttata) in a beaver-flooded bog in southern Ontario, Canada

Body temperature has a major influence on the physiological processes, growth, reproductive output, and overall survival of ectotherms. When a habitat is altered as a result of natural or anthropogenic influences, the available temperatures in the habitat can change, thus affecting an animal's ability to thermoregulate. We studied thermoregulation in response to habitat change in a population of spotted turtles (Clemmys guttata) in Southern Ontario, Canada. Historically, the study site was ditched to draw down water levels to facilitate peat mining, and the resulting drainage ditches were the only habitat containing surface water and turtles were restricted to these drains. Recent colonization of the site by beaver (Castor canadensis) caused increases in water level and water surface area. We followed spotted turtles (N=16) outfitted with radio transmitters and iButtons to estimate body temperatures (Tb) continuously throughout the active season post-flooding. Turtle models outfitted with iButtons (N=50) were deployed in the nine available habitat types to record environmental temperatures (Te). Turtles (N=13) were tested in a thermal gradient under laboratory conditions to determine preferred body temperature range (Tset). The Tset for the population ranged from 20 °C to 26 °C. In the field, Tb was within the Tset range 28% of the time from March to October, and 67% of the time from July to August. Efficiency of thermoregulation was calculated to be highest in July and August. The habitat type with the highest thermal quality was the shallow flooded zone created by beaver damming, and the habitat with the lowest thermal quality was the drain bottom, the drains being the only aquatic habitat available prior to flooding. This study confirms that beaver flooding provided a wide variety of preferable thermal opportunities for spotted turtles. Further investigation is needed to determine the effects of flooding on spotted turtle thermoregulation during nesting and hibernation.

► We studied thermoregulation by spotted turtles in response to flooding caused by beaver.
► The set-point temperature range (Tset) was 20–26 °C for turtles in our population.
► Tbs of turtles in the field were within Tset 28% of the time March–October, and 67% of the time July–August.
► Turtles maintained Tset in summer by thermoconforming with aquatic habitats created by beaver.
► In fall, turtles thermoconformed despite Tes below Tset, suggesting seasonal shift in Tset.