Spatial and Temporal Habitat-Use Patterns of Wood Turtles at the Western Edge of Their Distribution
Wood Turtles (Glyptemys insculpta) are a state threatened species at the western edge of their geographic distribution in Minnesota, United States. There is currently little published information regarding habitat use of western populations to assist with conservation initiatives. The primary purpose of this study was to investigate habitat use of a population of Wood Turtles in northeastern Minnesota to determine if habitat-use patterns were similar to other regions. In addition, we assessed the efficacy of two land-cover data sets (National Land Cover Dataset and LANDFIRE Existing Vegetation Type), relative to an aerial-photo–based habitat layer, for assessing habitat use and delineating preferred or avoided habitat classes. We performed this analysis to gauge the value of widely used habitat layers for Wood Turtle management and research. We used radio telemetry data collected on 8 males and 14 females between May and November 1990 to assess habitat associations and space-use patterns. We found that Wood Turtles heavily used and generally remained within 100 m of flowing water. Individuals also appeared to prefer other aquatic and semiaquatic habitats when not in or adjacent to flowing water. Despite this population inhabiting a primarily forested landscape, we found little evidence that forest habitat classes were preferred by this species; however, forest age could be an important variable, with younger, more open forest types being used more frequently. We found that neither NLCD nor LANDFIRE were adequate for assessing habitat associations or delineating habitat classes at the scale at which Wood Turtles use the landscape.Abstract
Number of male and female Wood Turtle (Glyptemys insculpta) observations relative to distance from the flowing water habitat class. The habitat class included the main river channel and associated tributaries for the study area in northeastern Minnesota, USA, and a 20-m buffer on either side of the flowing water bodies. The figure indicates the majority of individuals were located in or adjacent to flowing water.
Proportion of male (A) and female (B) Wood Turtle (Glyptemys insculpta) observations not in flowing water for each month of this study conducted along a river in northeastern Minnesota, USA. Black circles represent the mean (± 1 SD) proportion among individuals with the use of 8 and 14 radio-tracked males and females, respectively.
Relationship between distance from the flowing water and Julian day for male (A) and female (B) Wood Turtles (Glyptemys insculpta) along a river in northeastern Minnesota, USA, based on generalized additive models (GAM). The mean male and female distance from flowing water was 28.4 m and 37.3 m, respectively. The modeled distance increased by ca. 50 m during peak non–flowing water habitat use (mid- and late-July for males and females, respectively). The gray bands represent the approximate 95% confidence intervals for the smoothing curves, and the black circles represent the observed turtle distances with (left panel) and without (right panel) individuals treated as a random effects factor variable. The left panels were used for statistical analyses because of detected heterogeneity among individuals. The right panels are useful as a visual reference because they only include the actual observation points.
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