Winter movements of painted turtles, Chrysemys picta, in a Minnesota metropolitan lake
Summer behaviors and habitats of painted turtles, Chrysemys picta, have been well studied; however their winter behavior is far less understood. Seasonal freezing temperatures push physiologic limits for survival under ice and require behavioral adaptations during over-wintering periods. We estimate 500 painted turtles currently populate Lake Judy, a 6.5ha shallow lake located in a residential neighborhood of the Twin Cities in Minnesota. From September 2010-March 2015, we observed the movements of randomly selected Lake Judy painted turtles. During the summer months from June-August, we used 12 basking traps to capture and then radio-tag 41 turtles with as many as 10 radio-tagged per year. When safe ice conditions were present from December-March, we monitored turtle movements every 3-22 days by tracking each turtle to within 1m in order to determine the average and maximum daily distances and range of movement. Additional turtle movements were recorded from September-October 2010, April-May 2011, and May 2013 to provide a seasonal comparison of turtle movements in the absence of ice cover. Throughout the study, we recorded each turtle’s location by recording UTM (Trimble GPS with sub-meter accuracy) and freezing a colored paper tag on the ice for spatial comparison with previous date locations.
The average distance traveled by turtles under the ice from December-March 2010-2015 was 2.7m/day (range 0.15-46.3m/day) with a maximum total movement for one turtle of 1852m during one season. Average daily distances were also calculated for each month of winter, December-March. We found monthly variation in average daily distance with minimums in December (0.15m/day) and March (0.74m/day) of each year and maximums in January (2.7m/day) and February (3.2m/day). Our results show that turtles occupied shallower regions of the lake, especially along the shoreline where dissolved oxygen may exist in higher concentrations than in deeper regions of the lake. These observations suggest that movement may be limited by dissolved oxygen availability during the winter when ice and snow cover limit photosynthesis under the ice. As the most widely distributed species of turtle in North America, understanding the behavioral changes and adaptations of painted turtles to cold temperatures during the winter will allow us to better understand conservation and water quality requirements for a species at the northern extent of its range.