First Advisor

Catherine E. de Rivera

Date of Publication

Winter 3-19-2019

Document Type


Degree Name

Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources


Environmental Sciences and Resources




Corridors (Ecology) -- Oregon -- Wilsonville -- Case studies, Wildlife conservation, Wildlife crossings -- Oregon -- Wilsonville -- Case studies, Traffic safety and wildlife, Light pollution



Physical Description

1 online resource (xv, 187 pages)


While roads can present weak to complete barriers to wildlife, depending on the animal and traffic volume, mitigations such as under-crossings and green bridges on highways at least partially increase the permeability of the landscape to some of these species. The few studies evaluating the effectiveness of these structures for at least three years typically focused on a single species. Here, we monitored the crossing structure under Boeckman Road, in Wilsonville Oregon, for wildlife activity across summer seasons for ten years, since construction of the road and subsequent opening to traffic. This long-term multi-species dataset, which includes monitoring when the road was closed to traffic has provided a unique opportunity. Wildlife activity was collected using sand track pads monitored during summer seasons from 2009 to 2018. Wildlife activity showed a significant community level response from year to year and species-specific responses to year, vegetation change, disturbance, detection area, and previous experimental additions of artificial light.

Roads create barriers to animal movement through collisions and habitat fragmentation. Investigators have attempted to use traffic volume, the number of vehicles passing a point on a road segment, to predict effects to wildlife populations approximately linearly and along taxonomic lines; however, taxonomic groupings cannot provide sound predictions because closely related species often respond differently. We assess the role of wildlife behavioral responses to traffic volume as a tool to predict barrier effects from vehicle-caused mortality and avoidance, to provide an early warning system that recognizes traffic volume as a trigger for mitigation, and to better interpret roadkill data. We propose four categories of behavioral response based on the perceived danger to traffic: Nonresponders, Pausers, Speeders, and Avoiders. By considering a species' risk-avoidance response to traffic, managers can make more appropriate and timely decisions to mitigate effects before populations decline or become locally extinct.

Barriers to animal movement can isolate populations, impacting their genetic diversity, susceptibility to disease, and access to resources. Barriers to movement may be caused by artificial light, but few studies have experimentally investigated the effects of artificial light on movement for a suite of terrestrial vertebrates. Therefore, we studied the effect of ecological light pollution on animal usage of a bridge under-road passage structure. On a weekly basis, sections of the structure were subjected to different light treatments including no light added, followed by a Reference period when lights were off in all the structure sections. Findings suggest that artificial light may be reducing habitat connectivity for some species though not providing a strong barrier for others.

Through the work conducted herein we provide contributions to the understanding of how elements of the built environment impact wildlife communities ability to move across the landscape. Additionally, we provide new tools to support resource managers in barrier mitigation and connectivity planning. Habitat fragmentation effects are a complex set of issues that require resources and collaboration to reach meaningful solutions. The work presented here can also support decision-making, communication, and collaborative efforts that will ultimately result in on-the-ground impacts to reduce fragmentation effects and mitigate existing barriers effectively to promote the long-term viability of wildlife and the systems they depend on.


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