Movements, Habitat Use, and Thermal Ecology of an Isolated Population of Bog Turtles (Glyptemys muhlenbergii)
Because many species of semi-aquatic turtles have specific habitat requirements and unique life history characteristics, they are particularly vulnerable to anthropogenic habitat modification. The federally threatened Bog Turtle (Glyptemys muhlenbergii) requires specialized wetland habitats, such as bogs and fens, in the eastern United States and often occurs in isolated populations. To develop a more a detailed understanding of the habitat use, movement, and thermal biology of Bog Turtles, we radiotracked and monitored the temperatures of 11 adult Bog Turtles at an isolated Piedmont meadow bog in North Carolina from May 2007 to March 2008. We found that turtles used soft, shallow mud habitat in the bog, but moved to a streambed when the bog became dry. While in the bog, turtles were often found within or underneath woody debris. Although most turtles resided exclusively in the southern part of the bog and the stream, two male turtles made substantial over-land movements away from the bog exceeding 130 m. All but one turtle overwintered in a streambed adjacent to the bog. Turtles overwintering within stream habitat were not exposed to temperatures below 0°C, but one turtle that overwintered in the bog did reach below-freezing temperatures. This study suggests that high-quality bog habitat and habitat heterogeneity are critical for populations living in isolated and dynamic habitats. However, maintenance of corridors between suitable habitats may be necessary for the long-term survival of Bog Turtle populations.Abstract
Schematic diagram of the Bog Turtle (Glyptemys muhlenbergii) locations (crosses) within a bog in North Carolina, USA. The bog is primarily surrounded by mixed hardwood–pine forest. The bog is shaded gray; rectangular boxes indicate approximate overwintering locations of Bog Turtles. Eleven turtles are represented. Notice that some individuals (n = 3) traveled to the northern part of the bog for short periods of time, but the majority of turtle locations were within the southern part of the bog.
Relationships between turtle shell temperatures, shallow mud (A) and deep mud temperatures (B). Points represent the temperature recorded at each 30 min interval. Turtle shell temperatures correlated more closely with shallow mud temperatures than with deep mud temperatures, suggesting that turtles spent significantly more time in shallow mud than deep mud. Note that points above the regression line in A are assumed to represent basking events.
Mean daily maxima of turtle shell temperatures (Ts; n = 9) and shallow mud temperatures (Shallow Mud; n = 2). Shallow mud temperature fluctuated substantially during winter months, while turtle shell temperatures varied less. Biologically relevant events found through radiotelemetry are indicated on figure.
Daily maximum differences between Ts (turtle shell temperature) and shallow mud temperatures for four different turtles during the month of August. Each line represents one turtle. All four turtles stopped basking in mid-August. Radiotelemetry data indicate that these turtles moved to an adjacent stream at this time. We observed similar trends in temperature variation for the other five turtles throughout late August and September 2007.
Contributor Notes
Associate Editor: J. D. Litzgus.