Promoting Small Wildlife Highway Permeability: Assessment Of Design Criteria For Effective Passages And Cost-effective Monitoring Approaches

Focus Area

Wildlife & Ecosystems


Natural Resources






2-3 years

Research Idea Scope

There would be two parts to this study: 1) Literature Review and Synthesis of Current Practices and 2) Development of Cost-Effective Monitoring Techniques 1. Literature Review and Synthesis of Current Practices: There is a priority need to assemble and synthesize available information on the various design of existing crossing structures and their associated relative success in promoting passage for small mammals and herpetofauna, where known. This would entail compilation of information on existing infrastructure and any monitoring performed. It would be accomplished by a survey of the states and provinces across North America, as well as insights provided from Europe and elsewhere in the world, along with a thorough literature review. 2) Development of Cost-Effective Monitoring Techniques: As part of the evaluation of what structural design criteria most influence passage structure efficacy for small animals, cost-effective techniques that can be applied to conduct before- and after-construction monitoring of passage structure use by small animals will also be developed. Methods that have been used to date include roadkill tracking; soot-, sand- or dust-covered track pads; organism marking and experimental translocation; trappings within drainage structures; genetic analyses; radio or GPS animal tracking; and still images or video recording triggered by motion and/or infra-red sensors or with time lapse recording. Some of the methods are labor intensive, invasive to the animals being monitored, expensive to analyze or likely to miss some uses of the structure. Video footage from multiple cameras provides a wide variety of information compared to other methods but is very expensive to analyze. There may be ways to reduce labor needs for image processing through innovative software. Including cross evaluation of the costs and quality of data collected using different monitoring technologies (along the lines of Dodd and others 2004) would provide a toolbox of available techniques and direct comparison of their pros and cons for use with different species for practitioners to consider in monitoring connectivity projects.

Urgency and Payoff

Not only is it typically labor intensive and costly to rigorously monitor the effectiveness of structures in promoting small wildlife permeability across roadways, technical approaches to accomplishing such monitoring require refinement as well. Widely accepted, cost-effective approaches to monitoring the efficacy of passage structures for small animals are lacking, both because of methodology challenges (e.g., camera triggering sensitivity for small animals), as well as the ability to achieve meaningful sample sizes to support scientific inference (e.g., monitoring use by low density sensitive/listed species). Thus, assessment and refinement of methodologies for application in monitoring passage structure use and effectiveness for small animals is needed. To date, the effectiveness of passage structures for smaller terrestrial mammals and herpetofauna has not been systematically evaluated to the same degree as for larger species (van der Grift and others 2013). Our understanding of how structural design criteria affect use of passage structures by small wildlife is limited, especially compared to larger mammals. Increased understanding of the role of structural design criteria will inform project planning and design relative to whether existing structures are sufficient to accommodate passage, need to be upgraded/retrofitted, or require replacement with new structures. While NCHRP Project 25-25, Task 84 evaluated wildlife fencing and associated escape and lateral access control measures for the full range of wildlife, including small mammals and herpetofauna, survey information for smaller species is still relatively sparse compared to larger animals. A companion effort is needed to synthesize nationwide/regional efforts, to the degree information is available relevant to passage structures.

Suggested By

Kris Gade Arizona DOT 602-292-0301

[email protected]