Do roads reduce painted turtle (Chrysemys picta) populations?

Alexandra Dorland,Trina Rytwinski,Lenore Fahrig,Don A Driscoll

doi:10.1371/journal.pone.0098414

Abstract

Road mortality is thought to be a leading cause of turtle population decline. However, empirical evidence of the direct negative effects of road mortality on turtle population abundance is lacking. The purpose of this study was to provide a strong test of the prediction that roads reduce turtle population abundance. While controlling for potentially confounding variables, we compared relative abundance of painted turtles (Chrysemys picta) in 20 ponds in Eastern Ontario, 10 as close as possible to high traffic roads (Road sites) and 10 as far as possible from any major roads (No Road sites). There was no significant effect of roads on painted turtle relative abundance. Furthermore, our data do not support other predictions of the road mortality hypothesis; we observed neither a higher relative frequency of males to females at Road sites than at No Road sites, nor a lower average body size of turtles at Road than at No Road sites. We speculate that, although roads can cause substantial adult mortality in turtles, other factors, such as release from predation on adults and/or nests close to roads counter the negative effect of road mortality in some populations. We suggest that road mitigation for painted turtles can be limited to locations where turtles are forced to migrate across high traffic roads due, for example, to destruction of local nesting habitat or seasonal drying of ponds. This conclusion should not be extrapolated to other species of turtles, where road mortality could have a larger population-level effect than on painted turtles.

Highlights

Turtle populations have been declining over the past several decades [1,2,3,4]
Road mortality in particular is thought to be one of the primary causes of turtle population declines; for example, roads are reported as a principal threat to turtle populations in seven of the ten population status reports for turtle species listed on the SARA (Species at Risk Act) Public Registry [5]
We found no statistically significant difference in turtle relative abundance between Road and No Road sites, suggesting that the effects of road mortality, which we assume to be high at ponds near high traffic roads, may not translate into significant effects on population abundance

Summary

Introduction

Turtle populations have been declining over the past several decades [1,2,3,4]. Canada is home to eight species of freshwater turtles, each of which is listed as either endangered, threatened, or a species of special concern under the Canadian Species at Risk Act (SARA) in one or more of its regions of occurrence [5]. Turtle habitat destruction or alteration occurs through the construction or expansion of residential and commercial developments [2], [4], [8], [9]. Such development increases the risk of predation on turtles and their nests due to associated increases in abundances of common predator species associated with humans, such as raccoons (Procyon lotor), foxes (Vulpes vulpes), coyotes (Canis latrans) and domestic dogs (Canis lupus familiaris), and cats (Felis catus) [10], [11]. Road mortality in particular is thought to be one of the primary causes of turtle population declines; for example, roads are reported as a principal threat to turtle populations in seven of the ten population status reports for turtle species listed on the SARA (Species at Risk Act) Public Registry [5]

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Conclusion