Movement, habitat selection, and resource use by western painted turtles (Chrysemys picta bellii) in an urban environment near their northern range limit
Understanding resource use is necessary to properly manage and conserve habitats for long-lived species, especially for populations residing urban settings. I studied habitat selection, space use, and isotopic resource use of an urban population of western painted turtles (Chrysemys picta bellii) residing in Wascana Creek in Regina, Saskatchewan from May 2015 to April 2017. Using radio-telemetry to track movements, I determined habitat selection at multiple spatial (Johnson’s second and third order habitat selection) and temporal scales (active season; encompassing emergence, nesting, and post-nesting) using compositional analysis. I found that turtles selected for shoreline habitat over urban/parkland and open water (second order). The characteristics of the selected shoreline (third order) varied between habitat areas; however, they did not substantially differ across the active season. Within creek habitat, turtles chose shoreline habitat randomly. Within marsh habitat, turtles selected for particular shoreline features, preferring treed shoreline across all three periods of the active season. Across the active season, both male and female turtles moved significantly more during emergence than during nesting and post-nesting periods and movements were larger in marsh habitat than creek habitat. Suitable overwintering locations were limited within the study area, and were warmer and deeper than those randomly available, likely ensuring that their overwintering locations did not freeze. There was no significant difference in the dissolved oxygen level between used and available overwintering sites. I measured stable isotopes of carbon and nitrogen from nail samples to examine isotopic resource use within and among the populations in two habitats (marsh and creek). Isotopic niche size varied across the population as a result of variation in body size, sex, and location. Isotopic niches overlapped between 26-77%, with the least overlap between males and females. This indicates that although western painted turtles are generalist omnivores, there is indication of distinct isotopic resource use by subgroups. By comparing the isotopic values found in the turtles to those found in prey, I found that all turtles consumed low proportions of a wide variety of potential prey items, but there were differences among subgroups. Female and sub-adult turtles in the marsh consumed a higher proportion of crayfish and males consume a higher proportion of amphipods, whereas turtles in the creek consumed a higher proportion of chironomid larvae in comparison to the other available prey items. Turtles in this urban environment require aquatic systems with high productivity and diversity, vegetated shorelines to provide buffers from disturbance as well as provide suitable basking areas (i.e. banks with overhanging trees), and protected overwintering habitat that is at least 2 m deep. My findings indicate that turtles take advantage of a wide range of resources; however, there are particular requirements that are necessary to ensure their survival and long-term persistence in this environment.
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Faculty of Graduate Studies and Research, University of Regina