Crossing Corridors: Wildlife Use of Jumpouts and Undercrossings Along a Highway With Wildlife Exclusion Fencing

Abstract

Roads pose two central problems for wildlife: wildlife-vehicle collisions (WVCs) and habitat fragmentation. Wildlife exclusion fencing can reduce WVCs but can exacerbate fragmentation. In Chapter 1, I summarize the relevant studies addressing these two problems, with a focus on large mammals in North America. Chapters 2 and 3 summarize field assessments of technologies to reduce WVCs and maintain connectivity, specifically jumpout ramps and underpasses, along Highway 101 near San Luis Obispo, CA. In a fenced highway, some animals inevitably breach the fence and become trapped, which increases the risk of a wildlife-vehicle collision. Earthen escape ramps, or "jumpouts", can allow the trapped animal to escape the highway corridor. Few studies have quantified wildlife use of jumpouts, and none for >2 years. We used wildlife cameras to quantify wildlife use of 4 jumpouts from 2012-2017. Mule deer were 88% percent of our detections and jumped out 20% of the time. After accounting for pseudoreplication, 33% of the events were independent events, and 2 groups of deer accounted for 41% of all detections at the top of the jumpout. Female deer were 86% of the detections and were much more likely than males to return to the jumpout multiple times. This is the first study to document use of jumpouts for more than 3 years, the first to account for pseudoreplication, and the first to quantify differences in jumpout use between male and female mule deer. We recommend a jumpout height between 1.75m-2m for mule deer to increase the jumpout success rate. Chapter 3 addresses factors that may affect the use of undercrossings by mule deer and other wildlife. Wildlife crossings combined with v wildlife exclusion fencing have been shown to be the most effective method to reduce wildlife-vehicle collisions while maintaining ecological connectivity. Although several studies have quantified wildlife use of undercrossings, very few have exceeded 24 months, and the factors affecting carnivores use of the undercrossings remain unclear. We quantified mule deer, black bear, mountain lion, and bobcat use of 11 undercrossings along Highway 101 near San Luis Obispo, California from 2012-2017. We constructed zero-inflated Poisson general linear models on the monthly activity of our focal species using underpass dimensionality, distance to cover, substrate, human activity, and location relative to the wildlife exclusion fence as predictor variables. We accounted for temporal variation, as well as spatial variation by quantifying the landscape resistance near each undercrossing. We found that deer almost exclusively used the larger underpasses whereas the carnivores were considerably less selective. Bears used undercrossings more that were within the wildlife exclusion fence, whereas mountain lion activity was higher outside the wildlife exclusion fence. Bobcat activity was highest and most widespread, and was negatively associated with distance to cover. Regional connectivity is most important for bear and mountain lion, and the surrounding habita...

Spatio-Temporal Patterns and Consequences of Road Kills: A Review

“…Firstly, the recording and quality of road kill data can be compromised, hindering its utility in selecting or assessing mitigation measures [ 1 ]. Secondly, the mitigation measures may suffer from internal or external influences that compromise their effectiveness in preventing AVCs [ 116 ]. The main challenges associated with hindering the effectiveness of road kill prevention or reduction strategies, are discussed below.…”

“…The procedures, themselves, are necessary to prevent as many AVCs as possible. Currently implemented mitigation measures still face some challenges due to prevailing external conditions within the context in which they are used [ 116 ].…”

“…That is, fencing contributes significantly to road avoidance by animals [115]. Wildlife exclusion fencing is considered the most effective means to reduce AVCs [116]. A study by Rytwinski et al [117] confirmed that fencing reduces wildlife-vehicle collisions (WVCs) by 54%, regardless of whether they are combined with wildlife crossings.…”

“…As stated by Clevenger et al [115], AVCs can be clustered at fenced ends. When animals enter fenced rights-of-way from fence ends, they can become trapped between the road and this barrier, increasing their risk of being hit by an oncoming vehicle [116,127]. For instance, a 2 km road segment centered at the fenced ends of the Trans-Canada Highway, had a significantly high AVC rate [115].…”

“…For instance, a 2 km road segment centered at the fenced ends of the Trans-Canada Highway, had a significantly high AVC rate [115]. Jensen [116] states that fencing alone worsens the fragmentation effect of road infrastructure. As a consequence, fences that are not combined with wildlife crossing structures exacerbate the challenges faced by animals; as they try to maneuver from one habitat patch, to another.…”