Turtles in Suburbia: Habitat Usage in Suburban Retention Ponds

            In recent centuries, human activity has transformed Earth into something almost unrecognizable. Many of the biomes and wildernesses that once covered the planet barely exist anymore – enough so that some scientists suggest we create a new system of classification based primarily on how humans have shaped their environments, rather than on what organisms might theoretically occupy a given region had human development not occurred (Ellis & Ramankutty, 2008). Whether or not such systems end up becoming widely used, however, it is clear that human development is something that ecologists, if they want to understand how populations of organisms work today, need to deal with properly. Fortunately, many have taken up the call: studies of urbanization’s effects on plants and animals are now commonplace. Less common, however, are suburban studies that treat suburban areas as more than an intermediate between “city” and “wilderness” – even though an increasing amount of the U.S. population in particular resides in suburban areas. Recently, however, ecologists have started to look at the suburbs from a different perspective, examining the habitat features unique to these areas and how plants and animals interact with them

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Figure 1: Location of the study site within the Australian Capital Territory (ACT).

            One particularly insightful perspective into these specifically suburban habitats is “Suburbs: Dangers or Drought Refugia for Freshwater Turtle Populations?” (Roe, Rees, & Georges, 2011). The authors hoped to study whether suburban retention ponds in Canberra, Australia provided lower or higher-quality habitat than nearby nature preserves for eastern long-necked turtles (Chelodina longicollis). They determined this by trapping and tagging turtles over the course of a year, measuring recapture rates and growth rates of recaptured individuals over time, and by taking size and water quality measurements of the bodies of water in the study areas. Despite initial suspicions that these retention ponds might be detrimental to the turtle populations – luring turtles in but then harming them with poor water-quality and low food abundance – the study actually found that turtles in the suburbs grew faster and larger than those in the nearby nature preserves. This suggests that, particularly during times of drought such as the year during which this study occurred, the humble suburban retention pond might serve as a valuable refuge for local wildlife, and should be managed with this ecological function in mind.

Figure 2: Growth rate (y-axis) vs. initial carapace length (x-axis) for turtles in the suburbs (dark circles, solid line) and nature preserves (white circles, dashed line).

            Inspired in part by this study, I intend to carry out my own research on distribution and movement of muskrats (Ondatra zibethicus) in suburban water retention ponds. Although these particular researchers were not certain as to what factors might make the suburbs a better habitat for turtles than the nature preserves – none of the water quality or pond size metrics that they recorded seemed to suggest an explanation – their findings nonetheless suggest that these may be more than just universally “low-quality” habitats. What applies to turtles, however, may not necessarily apply to many of the other species that thrive in these developed areas. By studying how muskrats – another species commonly found in the suburbs, albeit in the United States rather than in Australia – interact with these anthropogenic habitats as opposed to those in more “natural” areas, I hope to build off the research done by Roe, Rees, and Georges in order to further develop our understanding of suburbia not just as an awkward in-between of urban and rural zones, but as a kind of human-made biome that needs to be understood (and managed) as such.

Works Cited

Ellis, E.C., & Ramankutty, N. (2008). Putting people in the map: Anthropogenic biomes of the world. Frontiers in Ecology & the Environment, 6(8), 439-447.

Roe, J.H., Rees, M., & Georges, A. (2011). Suburbs: Danger or drought refugia for freshwater turtle populations? The Journal of Wildlife Management, 75(7), 1544-1552. Retrieved from http://www.jstor.org/stable/41418195.