The greatest driver of the current global biodiversity crisis is habitat loss. Roads are a major contributor to habitat loss because they destroy and fragment habitat, in addition to causing direct mortality. Animals may respond to roads either by avoiding them, thus leading to population isolation, or by attempting to cross them, thus potentially leading to increased mortality and, if so, also to population isolation. I studied the impact of road density on abundance of two northern snake species: the redbelly snake (Storeria occipitomaculata) and the garter snake (Thamnophis sirtalis). I hypothesized that roads are detrimental to snake populations due to road avoidance and road mortality. Therefore, I predicted that snakes should be less abundant at sites with higher road density in their surroundings. I also hypothesized that snakes in areas of high road density would be killed on roads before reaching full size. Therefore, I predicted that snakes should be smaller at sites with higher road density in their surroundings. I deployed cover boards at 28 old field sites along a gradient of road density in 2020-2021. I visited sites weekly, counted the number of unique individuals, and measured them.
I captured fewer garter snakes at sites surrounded by more roads, and fewer redbelly snakes at sites surrounded by more urban areas. Snakes were larger at sites more enclosed by roads, and surrounded by more roads. These effects were not strong, however, suggesting that though roads do have an impact on populations of northern snakes, that effect may be small relative to other factors. Perhaps garter and redbelly snakes are more resilient to the effects of roads and urbanization than other northern reptile species given their small size, and thus restricted movements, and their extensive use of disturbed habitats such as old fields.