Suggested Citation:
Shilling, Fraser M. (2018) NCST Policy Brief: Traffic Noise and Light May Affect Wildlife Use of Highway Crossing Structures. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-18-22

Connectivity of wildlife populations and communities of interacting species are disrupted by roads and highways. Wildlife crossing structures (WCS) over or under highways have been proposed as a solution for road-related habitat fragmentation and wildlife collisions. To assure the efficacy of WCS, road-related negative impacts that could cause animals to avoid WCS, such as noise and light, need to be considered. Human-sourced noise can affect habitat occupancy, and a suite of animal behaviors such as vigilance, communication, and predation efficiency, while artificial light, especially at night, can change animal’s perception of resources, foraging, mate selection, and navigation. Furthermore, the impact of noise and light varies among wildlife species, leading to differential responses within wildlife communities.

To test whether traffic noise impacts species’ use of WCS, the researchers quantified overnight (afternoon to early morning) road traffic noise, measured as dB(A), at 20 WCS positioned along four central California highways (I-5, I-80, 680 and 280), as well as historical WCS mammal use for 20 recorded days during the summer of 2012, 2015, and 2016. They also measured light intensity as total luminescence at eight WCS in the Sierra Nevada and San Francisco Bay Area. The researchers used a novel approach employing a camera with a very wide-angle lens to capture low light levels, combined with software that estimates total illumination and light frequency. Results indicate that wildlife use of WCS could be disrupted by traffic, especially for disturbance-sensitive species. This has important ramifications for using WCS as primary approach to resolve road/highway disruption of wildlife movement and occupancy.