Effects of roadside maintenance on reptiles and amphibians

Authored by Katie Black and Clay Shearer

We’d like to thank Fred Schueler, Dave Seburn, and Sheldon Lambert for sharing their thoughts on the topics addressed in this post.

During our surveys, we’re accustomed to seeing routine roadside maintenance including vegetation management and grading of road shoulders. Vegetation management includes using a mower or chainsaw to improve motorist visibility of roads, ditches, road signs, and guardrails. It also includes applying herbicide such as glyphosate, which is the active ingredient in Roundup. Road grading involves levelling and re-shaping the unsealed shoulders with a grader that’s towed behind a vehicle.

Roadside maintenance can interact with wildlife in several different ways, some of which may be beneficial, though overall are likely to be negative. Mowing can directly injure and kill animals such as amphibians and snakes (Danby et al., 2016), but we’ve also found that milksnakes like to hide under the grass thatch left behind from mowing: https://www.inaturalist.org/observations/170205911

Suppression of vegetation through herbicide use may create turtle nesting sites by exposing substrate and reducing shading (F. Schueler, pers. comm.). However, the spraying of herbicides could potentially harm turtle nests along roadsides, though there’s minimal research on this. De Solla et al. (2011) demonstrated that typical field application rates of herbicide for corn production in Ontario may not be a major threat to Snapping Turtle hatchling success. In contrast, Mendonça et al. (2023) studied the effects of glyphosate on the Amazon turtle using commercial formulation measurements and found that it interfered with eggshell chemical composition, reducing moisture content, crude protein, and increasing ethereal extract. These effects could cause alterations in the mobilization of water and nutrients essential for proper development of the turtle embryo.

Roadside grading may also interact with turtle nests as it usually occurs throughout the nesting and incubation period (i.e., May through September). Grading may occur above nest depth but can lead to further burying and/or compaction of nests (Marchand & Litvaitis, 2004). Since nests are already belowground, it’s not clear if this is harmful. If grading does occur at nest level, it could cause direct damage to nests, and this may be of particular concern for turtle species that excavate shallower nests. We and the local experts we’ve consulted have never seen a turtle nest that was obviously destroyed by grading, but we suspect it happens. Further studies are needed to better understand the effect of roadside grading on turtle nests. Potential mitigation includes limiting grading to outside of the nesting and incubation period, but this may be challenging for municipalities given the seasonal constraints associated with grading. Another option is to pave road shoulders; this would remove nesting habitat, but considering the dangers associated with nesting along roads (e.g., adult and hatchling road mortality), this may be the best option while also reducing maintenance needs (D. Seburn, pers. comm.).

In addition to vegetation management and roadside grading, guardrail work can impact animals that use roadside habitats. The replacement of guardrails during the turtle nesting and incubation period can directly disturb nests (S. Lambert, pers. comm). The extensive use of road salts in de-icing can also be harmful, particularly to aquatic and semi-aquatic organisms (Arnott et al., 2020). For example, high chloride concentrations in roadside ditches and wetlands can reduce embryonic and larval survival of amphibians (Karraker et al., 2008) and alter amphibian community structure by excluding salt intolerant species (Collins & Russell, 2009).

Ultimately, roadsides can create artificial habitat for a variety of species, but routine maintenance can cause negative effects in the absence of mitigation. There are several helpful resources available that provide recommendations for best management practices, including Turtle Nests - Road Shoulder Maintenance Management Best Practices: A Guide for Municipalities (Berman, 2017) and Best Management Practices for Mitigating the Effects of Roads on Amphibian and Reptile Species at Risk in Ontario (OMNRF, 2016).

Thanks for stopping by!


Arnott, S.E., Celis-Salgado, M.P., Valleau, R.E., DeSellas, A.M., Paterson, A.M., Yan, N.D., Smol, J.P., and Rusak, J.A. 2020. Road salt impacts freshwater zooplankton at concentrations below current water quality guidelines. Environmental Science & Technology, 54: 9398–9407.

Berman, L. 2017. Turtle nests-road shoulder maintenance best management practices: A Guide for Municipalities. Available online at: https://centrehastings.civicweb.net/document/30761/TURTLE-NESTS-ROAD-SHOULDER-MAINTENANCE-BEST-MANAGE.pdf?handle=E8A6A26CA3F240A797C08C15BF6DE949 [Accessed 1AD].

Collins, S.J., and Russell, R.W. 2009. Toxicity of road salt to Nova Scotia amphibians. Environmental Pollution, 157(1): 320-324.

Danby, R., Karch, M., Shearer, C., Schueler, F., and Smith, C. 2016. Highway 401 (Gananoque to Brockville) Species at Risk road ecology project 2014-2016. Prepared for the Ontario Ministry of Natural Resources and Forestry Species at Risk Stewardship Fund (Project #1-14-A2A). Algonquin to Adirondacks Collaborative, Landsdowne, ON, and Ontario Road Ecology Group, Toronto, ON.

De Solla, S.R., Martin, P.A., and Mikoda, P. 2011. Toxicity of pesticide and fertilizer mixtures simulating corn production to eggs of snapping turtles (Chelydra serpentina). Science of the Total Environment, 409(20): 4306-4311.

Karraker, N.E., Gibbs, J.P., and Vonesh, J.R. 2008. Impacts of road deicing salt on the demography of vernal pool-breeding amphibians. Ecological Applications, 18(3): 724-734.

Mendonça, J.D., de Almeida, J.C.N, Lucélia Gonçalves Vieira, L.G., Hirano, L.Q.L, Santos, A.L.Q, Andrade, D.V., Malafaia, G., de Oliveira, R.J., and Beletti, M.E. 2023. Mutagenicity, hepatotoxicity, and neurotoxicity of glyphosate and fipronil commercial formulations in Amazon turtles neonates (Podocnemis expansa). Science of the Total Environment, 898: 165529.

Marchand, M.N., and Litvaitis, J.A. 2004. Effects of landscape composition, habitat features, and nest distribution on predation rates of simulated turtle nests. Biological Conservation, 117(3): 243-251.
Ontario Ministry of Natural Resources and Forestry. 2016. Best Management Practices for Mitigating the Effects of Roads on Amphibians and Reptile Species at Risk in Ontario. Queen’s Printer for Ontario. 112 pp.

Posted on September 01, 2023 02:45 PM by knoir knoir


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