Ecology and Vulnerability

Wood Turtle

Background
The wood turtle is closely associated with rivers and streams, spending the majority of its time in the water¹.  However, during the active period of summer, it may spend considerable time away from water foraging for food, even becoming mostly terrestrial for periods of time^2,3.  These forays into the landscape can make it vulnerable to mortality from road crossings, agricultural machinery, and mammal attacks⁴.  In addition, wood turtles are highly sought by collectors³.  Because the species is long lived (up to 58 years) and has low reproductive rates, loss of individuals can greatly impact populations^1,3.  Increased fragmentation of habitat and human disturbance has led to declines throughout the range and the species is currently listed as endangered on the IUCN Red List⁵.  

Climate Impacts
As with other reptiles, wood turtles have limited physiological control over body temperature and must regulate their temperature through habitat selection and behavior⁶.  Wood turtles will bask in the sun to raise their body temperature and the amount of time spent basking appears to decrease during the warmer months (July and August)^6,7. When turtles start basking in the spring is related to air temperature and will begin when a certain temperature threshold is reached.  Air temperature thus directly controls the length and intensity of the active period for wood turtles.  Ambient temperature also appears to play a role in terrestrial activity.  More time spent basking decreases the amount of time spent foraging in the landscape⁶, but turtles also will retreat to a stream when air temperatures are cool, using the water as a thermal (temperature) refuge ^6,8. 

In northern populations, these requirements for thermoregulation (maintaining body temperature) limit the spatial distribution of turtles so that terrestrial activity is decreased⁶.  In these populations, turtles will remain closer to streams, using water as a thermal refuge as nighttime temperatures fall^6,9,10.  Additionally, length of winter hibernation is related to climate³.  Because behavior is so closely tied to temperature in this species, it seems likely that climate change could directly affect behavior, though population responses are unknown.  However, one study found that clutch frequency (rate that batches of eggs are laid) increased with increasing autumn temperatures in a northern population of painted turtles, suggesting potential effects on reproductive output¹¹.  It is possible that increased terrestrial activity associated with higher temperatures could also increase harmful interactions with humans.

Additionally, wood turtles may be displaced up to several kilometers downstream during flood events^4,12.  Increases in precipitation, especially rain, during winter are projected for the Northeast, potentially resulting in increased frequency and severity of high flow flood events during this period^13,14,15.  A study of wood turtles in Massachusetts showed that floods displaced nearly half of the subpopulation annually, resulting in elevated mortality rates and decreased breeding success¹².