Behavioral responses of two syntopic snakes (genus Thamnophis) to roads and culverts
Habitat fragmentation can be a major contributor to the loss of biodiversity within terrestrial ecosystems. Roads are a major contributor to fragmentation, presenting hazards as well as potential barriers within landscapes. Impacts of fragmentation by roads include mortality, loss of gene flow, and possible disintegration of population structure. These effects may be even more pronounced for wetland wildlife, given the compounding effects of a lack of aquatic corridors between individual wetlands distributed through the landscape. In order to mitigate these impacts of roads, it is necessary to identify methods for controlling when and where animals cross roads as well as provide safe corridors that species are willing to utilize "through" the barriers imposed by roads. In order to investigate potential methods for reducing road impacts, I examined the behavior of two species of wetland-associated snake, the Eastern Gartersnake (Thamnophis sirtalis sirtalis) and the Eastern Ribbonsnake (Thamnophis sauritus sauritus). These impacts were studied at Muscatatuck National Wildlife Refuge in southern Indiana, where there are large populations of the target species, and several roads transect the property, providing ample test opportunities. In Chapter One, I investigated the influence of canopy cover and road substrate on crossing behavior and frequency of crossing by Eastern Gartersnakes and Eastern Ribbonsnakes. Both of these species were observed to avoid roads with relatively low crossing rates for both species in all treatments. Roads were thus confirmed to be barriers for the movement of both species regardless of canopy cover or road surface. However, both species were also more willing to cross roads with canopy cover regardless of substrate. These results provide information that is important when managing for snake road crossings that were identified as beneficial sites and discouraging crossings in non-advantageous sites. In Chapter Two, I used two experimental approaches to explore the minimal culvert design that both species of snakes would use. I also examined in-place culverts at the refuge to determine if snakes used culverts currently within their habitat. I found that snakes generally did pass through culverts of a diversity of sizes, with the lowest crossing frequency being eighty-four percent for culverts with a greater diameter (≥ one meter), regardless of substrate. The same trends were observed for the in-place culverts where larger culverts (i.e. lowest crossing frequency eighty percent) encouraged higher crossing rates than smaller culverts (i.e. highest crossing frequency twenty-seven percent). These results provided data on the optimal culvert configurations which could aid management and reduce road mortalities. Overall, these species showed very similar behavioral responses to both road and culvert encounters. These similarities between road and culvert crossings by the two species simplify management efforts and will potentially be beneficial for additional wetland species. These findings have the potential to help officials make informed management decisions it is also a starting point for future research in road mitigation of wetland species.
Kingsbury, Purdue University.
Conservation|Animal sciences|Behavioral Sciences
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