Animal Crossing: New Research Guides Efforts to Protect California’s Amphibians and Reptiles from Road Danger

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Roads can be dangerous for California’s reptiles and amphibians, but a five-year study and new video show that there are effective strategies to help these animals cross roads safely.

The California Department of Transportation (Caltrans) released the results of the study this week in a comprehensive, evidence-based best practices guide that explains approaches and techniques for minimizing the impact of roads on fragile and diminishing habitats and species, including frogs, toads, salamanders, turtles, lizards and snakes.  

A Yosemite toad on a road

A Yosemite toad on a road. Amphibians and reptiles are particularly susceptible to negative effects of roads within their habitat.

(Credit: Cheryl Brehme, USGS Western Ecological Research Center. Public domain.)

The best practices guide is the first of its kind for amphibian and reptile management and conservation near California roads.

“It is no longer a case of putting a few pipes and fences into the ground with a ‘fit and forget’ approach,” said Tom Langton of Herpetofauna Consultants International, Ltd., primary author on the guidance document. “This guide offers resource managers in California opportunities and a clear plan to improve existing crossings and build new ones to better standards where they are most needed. The guidance should be valued in other states with similar wildlife-road issues and at the international level, too.” 

Many reptile and amphibian species must cross roads to reach essential breeding and foraging habitat, are slow moving or are too small for drivers to see and avoid. Snakes and lizards may also be attracted to paved roads that typically absorb and retain heat.  All these behaviors put them at high risk of vehicle collisions.  

“We have a responsibility to maintain the highway system in a way that doesn’t impede or disrupt wildlife, including the movement of California’s threatened and endangered reptile and amphibian species,” said Caltrans Director Toks Omishakin. “This study allows us to analyze feasible and effective ways Caltrans can use ecologically-minded design to minimize impacts on these wildlife populations.”    

Traditionally, transportation agencies and wildlife managers have installed structures to help amphibians, reptiles and other small animals cross highways safely, such as tunnels under roads or barrier fencing.

“While agencies have made significant investments in these structures for many years, there has been little research into how effective they are,” said Dr. Robert Fisher, a U.S. Geological Survey (USGS) supervisory ecologist involved in the study. “Management guidance informed by science is needed to help ensure this critical infrastructure is safe for sensitive species.”  

With these concerns in mind, the goals of the collaborative project were to address this information gap using a logical framework and to help transportation agencies like Caltrans plan barrier and crossing structures more effectively. 

To help Caltrans determine which reptile and amphibian species to prioritize, USGS scientists created a ranking system for more than 160 species and sub-species, based on their vulnerability to road dangers. Turtles, tortoises and snakes dominated the highest risk category. USGS also developed a mapping system to allow Caltrans to easily find where the ranges of high-risk species overlap with California highways and statewide conservation efforts. Species ranked high and very-high risk of negative road-related impacts include desert tortoise, California red-legged frog, sierra newt and red diamond rattlesnake, among others.  

A Yosemite toad looks through a mesh fence, holding itself up on its back legs

A Yosemite toad looks through mesh fencing alongside a road used to mitigate negative road impacts and guide amphibians towards safe passages.

(Credit: Cheryl Brehme, USGS Western Ecological Research Center. Public domain.)

Then, in a series of field experiments, the USGS scientists investigated how reptiles and amphibians interact with different types of fencing, how far high-risk migrating amphibians move along road barrier fencing before “giving up” or finding a passage, and the effectiveness of turnarounds at fence ends.  

“We were happy to find that turnarounds at barrier fence ends were largely effective in changing the trajectory of many species to help lead them back toward a passage,” said Cheryl Brehme, the USGS project lead. A new video by USGS shows a California tiger salamander successfully make it to an underground crossing after being guided by one of these turnarounds. 

USGS and partners also designed and tested of a new type of passage structure called an elevated road segment.

“The elevated road-segment is really exciting,” said Brehme, “because it can be made to any width and length enabling reptiles, amphibians and other small wildlife species to freely move back and forth across wide stretches of roadway.” 

Caltrans used the results of these combined studies to produce the best management practices guide, which will inform the work of district biologists and engineers and will likely be useful to many other organizations involved in the planning and construction of transportation infrastructure. USGS has also released a comprehensive report of its studies in conjunction with the new guidance document.  

The guide emphasizes that different landscapes – and different species – need a range of solutions, and the needs of different species and their numbers will influence positioning and sizes.

“Planning for smaller rare species calls for designs that take into account the sensitivities and needs of these understudied and often forgotten species” said Dr. Tony Clevenger of Western Transportation Institute, who led the development of the best management practices guide.

The best practices guide was produced for Caltrans by the Western Transportation Institute of Montana State University with Herpetofauna Consultants International, Ltd and is based on existing knowledge and foundational studies by the U.S. Geological Survey Western Ecological Research Center. 

Video Transcript

This video shows a California tiger salamander finding its way to an underpass designed to help amphibians and reptiles cross the road safely, with the help of a "turn-around" that helps guide the salamander back in the right direction as it travels away from the underpass. The salamander was caught on wildlife cameras at various points between the turn-around and the underpass as part of a USGS study to understand how California tiger salamanders use turn-arounds and passage structures. The study was part of a larger project to develop science-based guidance for road agencies to help reptiles and amphibians cross roads safely.

Allie Weill, USGS Western Ecological Research Center

(Permission granted to USGS for some imagery and video.)