Ecology and Conservation of
the Wood Turtle (Clemmys insculpta) in Maine.
 

by

Bradley W. Compton
University of Main

Wood turtles (Clemmys insculpta) have declined throughout their range. They are listed as Special Concern, Threatened, or Endangered in most states in the U.S., and are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES).  Little is known about the ecology and conservation status of wood turtles in northern New England.  I studied conservation issues and habitat selection in a population in western Maine, and evaluated temperature as a potential limiting factor for wood turtles at the northern extent of their geographic range.

I observed that nesting success can be extremely low during short, cool summers.  A degree-day model of incubation time was applied to historical weather data from accross the wood turtle's range to estimate the proportion of years that eggs could successfully hatch, and predict the northern range limits of the wood turtle.  The model supports the hypothesis that incubation temperature determines the northern range limits of wood turtles.

Wood turtles in western Maine move among several widely-separated "activity areas" throughout the summer.  I modeled habitat selection at two scales.  I used paired logistic regression to model selection within turtle activity areas, and logistic regression to model selection of activity areas within the watershed.  Within activity areas, wood turtles selected nonforested locations close to water with low canopy cover.  Within the watershed, they selected activity areas close to streams and rivers with moderate forest cover and little open water.  The difference between selection at these two scales suggests that wood turtles select forest edges to balance thermoregulatory and feeding needs.  The model of selection of activity areas within the watershed correctly classified 84% of activity areas and random areas.  This model may be useful for identifying wood turtle habitat across the landscape as part of regional conservation efforts.

Anthropogenic threats to wood turtle populations in Maine include damming of rivers and streams, degradation of riparian habitat, road mortality, and collection as pets.  About one-quarter of nests at my study site are destroyed annually by water releases from an upstream dam.

I used GIS to compare 2,019 turtle locations in 1997 and 1998 with zones protected by riparian and watershed regulations in Maine as a test of how well these regulations protect wood turtle habitat in my study site.  Maine's Shoreland Zoning Ordinance and Champlain International Corporation's Riparian Management Guidelines protected 80 - 85% of turtle locations from intensive forestry, whereas the Land Use and Regulation Commission (LURC) riparian regulations for the less-populated half of Maine protect only about 17% of turtle locations.  Buffer zones designed to protect 99% of wood turtle locations would have to extend 300 m from rivers, streams, and large wetlands.

I built a simple demographic model to estimate the effect of the annual removal of a small number of adults from a hypothetical population of wood turtles. The model indicated that removal of a single adult annually from a stable population of 100 adult turtles would cause a 60% decline in over 100 years, and that removal of two animals annually would extirpate the population in less than 80 years.

These analyses suggest that wood turtles are particularly vulnerable near their northern range limits.  Efforts to protect riparian habitat, minimize flooding and other disturbances at nest sites, and to protect adults from collection as pets will be necessary to conserve wood turtles in Maine. 

© Bradley W. Compton  1999

 Abstract Reproduced with Permission of Author


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