Fine-scale habitat use and movement of wood turtles (Glyptemys insculpta) in the northwoods of Maine and Vermont.
biology , wood turtle , Glyptemys insculpta , Maine , Vermont
Marchacos, Sierra R.
The wood turtle (Glyptemys insculpta) is a freshwater, semi-aquatic species that has been experiencing widespread population decline. They are listed as a species of concern in all states and provinces in which they are found. The cause of these declines is primarily due to anthropogenic threats, such as illegal collection from the wild, habitat fragmentation, and mortality from agricultural machinery. The habitat use and space use of wood turtles has been studied across their range, but data-deficient areas of northern New England could be critical to conserving this species into the future. Two populations of wood turtles in northeastern Vermont and western Maine were discovered in 2018 on large tracts of remote, conserved land. These populations could be critical to the conservation of wood turtles in the northeast. The movement and fine-scale habitat selection of these two wood turtle populations was analyzed to inform management strategies that help sustain these wood turtle populations. This research also provides baseline data for populations located in relatively unfragmented habitat. Thirty-four wood turtles were fitted with VHF radio transmitters and 30 with GPS tags. The turtles were tracked via VHF radio telemetry from May-September in 2019 and 2020. The GPS tags were programmed to take a series of locations every day during the active season from June-September. These spatial data were analyzed to estimate home range size using both the 95% MCP and AKDE methods. These estimates were tested for differences between study areas, sexes, and estimation methods using a t-test. Using a linear mixed-effects model, comparisons were made to test for differences between sexes and study areas for both the distance moved and distance from the river. The females at the Maine study site had larger home ranges than the males. The males at the Vermont study area had larger home ranges than the females. The turtles in Maine had larger home ranges than the turtles in Vermont. In general, males tended to stay close to the river, or in the river. Females moved perpendicularly away from the river more often than males. Results from the mixedeffects model showed marginally significant differences with males staying closer to the river than females. Females made the longest movements during the course of the study. The furthest recorded distance from the river was 786 m from a VHF location on a female. The furthest distance from the river recorded with a GPS tag was 520 m from a female. The GPS data captured large overnight movements greater than 500 m by females moving between nest beaches. Both male and female turtles were recaptured at locations over 3000 m apart during a single season. The mixed-effects model showed that on average, males made significantly longer movements than females despite the females having larger movements during the nesting season. In 2019 habitat data were collected at used and paired random plots to analyze fine-scale habitat selection by wood turtles. A generalized linear mixed-effects model was used to analyze third-order habitat selection. The predictor variables tested in the models included different classes of vegetation cover, overstory density, sun exposure, distance to moving water, total food presence, number of stems, and mean DBH of trees. Model-averaged parameter estimates indicated that the mean DBH of trees and forb and herbaceous vegetation cover had a strong negative effect on turtle habitat selection, meaning higher mean DBH and greater cover of forb and herbaceous vegetation was less favorable. Shrub cover had a marginally significant positive effect. Tree cover and number of stems were explored further after removing variables with multicollinearity. Tree cover had a significant negative effect on habitat selection. Greater mean DBH and number of stems had a significant negative influence on habitat selection, and woody debris had a marginally significant positive effect. The majority of turtles utilized the floodplain, riparian, and river cover types. Other cover types used were wetland, vernal pool, forests, roads, and clear-cuts. Wood turtles choose areas with open canopy likely to meet thermoregulatory needs, and complex vegetative structure like shrubs and woody debris most likely because they foster a variety of food sources. The results from this research can be used to inform management, and are an initial look at the relationship between wood turtles and timber management. Management recommendations are given based on the results from the movement and habitat data, such as restricting harvest to the winter months, seasonal road closures, and future research on the impact of timber harvests on wood turtle populations.