This subject area consists of various taxonomic groups commonly addressed by Caltrans" biologists for transportation projects and operations: invertebrates, amphibians, reptiles, birds, and mammals.

Many are threatened and endangered species that require specialized surveys and resource agency permits and coordination. Wildlife habitat connectivity and movements are important issues being addressed for transportation projects throughout the State of California. Bioacoustics and noise effects on wildlife is an emerging issue which should be considered. The Caltrans Standard Environmental Reference, Volume 3 been developed in order to provide guidance, tools, and references, to help in the evaluation of wildlife in relation to transportation projects, facilities, and operations. If you need further assistance regarding a particular topic or issue, please feel free to contact the individual identified at the web page for information on that particular subject of interest.

"Special-status species" is a general term that refers to all species that are considered to be of interest biologically, regardless of their legal or protection status. Visit the Caltrans Standard Environmental Reference for more clarification on the term "Special-status species." It has information on how to facilitate such coordination and what resources will be needed during these processes.

Special-status species generally fall into one or more of the following categories:

  • Officially listed as Threatened or Endangered or Proposed Threatened or Proposed Endangered for listing under the California and/or Federal Endangered Species Acts.
  • California or Federal Candidate for listing.
  • Species that are biologically rare, very restricted in distribution, declining throughout their range, or have a critical and/or vulnerable stage in their life-cycle that warrants monitoring.
  • Populations in California that may be on the periphery of a species’ range, but are threatened with extirpation within California.
  • Species closely associated with a habitat that is declining at an alarming rate (e.g., wetlands, riparian woodlands/forests, old-growth forests, desert aquatic ecosystems, native grasslands, vernal pools, etc.).
  • Species designated as a ‘special status’, sensitive, or declining species by other state or federal agencies, or non-governmental organizations (NGOs).

Wildlife Links

  • CA Department of Fish and Wildlife: Species considered by Department of Fish and Game to be a Species of Special Concern (SSC). More information on California Species of Special Concern is available.
  • Biogeographic Information and Observation System (BIOS): The California Department of Fish and Wildlife developed the Biogeographic Information and Observation System to manage and facilitate the use of biogeographical data with partner organizations.
  • U.S. Fish and Wildlife Service: Note: A Federal Species of Concern list is no longer maintained. Information can be found on the U.S Fish and Wildlife Service website.

Wildlife Crossing/Connectivity

What Are Wildlife Crossings & Why Do They Matter?
Wildlife crossings are areas of concentrated animal movement intercepted by roadways. In most cases, effects are seen because animals are inadvertently hit by drivers as they attempt to cross the road surface, leading to mortality of animals (“road-kill”) and safety concerns to the motoring public. In other cases, animals choose to avoid crossing, and the roads present barriers to animal movement, dividing a formerly single population into two or more isolated population
segments, causing a range of negative effects. These effects may be less apparent, but are no less significant. Further, environmental regulations compel transportation professionals to reduce or eliminate effects on special status species and habitats.

  • USGS - Research to Inform Caltrans Best Management Practices for Reptile and Amphibian Road Crossings (PDF) 
    This project was part of a broader collaborative effort between the Western Transportation Institute (WTI) of Montana State University and USGS Western Ecological Research Center (WERC). As part of this broader project, WTI conducted a worldwide literature review and gap analysis and produced a BMP manual for herpetofauna in California (Langton and Clevenger 2020). WTI and USGS were contracted separately although USGS worked closely together throughout this broader effort and each brought particular expertise to the project. This research was provided by USGS and Caltrans considers the need for barrier structures and safe wildlife road-crossings important to maintain the long-term viability of wildlife populations. To prioritize these efforts for herpetofauna, USGS identified species that are most at risk of extirpation from road-related impacts. With over 160 California species and a lack of species-specific research data, we developed an objective risk assessment method based upon road ecology science. Risk scores were based upon a suite of life history, movement, and space-use characteristics associated with negative road effects that were applied in a hierarchical manner from individuals to species. Considerations included movement distances, movement frequency, speed, habitat preferences, movement behavior (territorial, non-territorial, vs. migratory), fecundity, range size and conservation status. All California herpetofauna species (and some subspecies) were ranked into five relative categories of road-related risk to both aquatic and terrestrial connectivity (very-high to very-low) based upon 20% increments of all species scores. A list of high and very-high risk species is provided in this research.
  • Western Transportation Institute - Measures to Reduce Road Impacts on Amphibians and Reptiles in California: Best Management Practices and Technical Guidance (PDF)
    A five-year study has produced a wealth of new information on the risks to amphibians and reptiles in California, and state-of-the-practice guidance for road agencies on ways to protect and recover sensitive species.
    The California Department of Transportation, Division of Research, Innovation and System Information funded and recently released Measures to Reduce Road Impacts on Amphibians and Reptiles in California: Best Management Practices and Technical Guidance. It was produced in close partnership with the Western Transportation Institute (WTI) of Montana State University and USGS Western Ecological Research Center (WERC). The 120 page guidance best practices document here explains approaches and techniques for minimizing the impact of new and improved road networks on fragile and diminishing habitats and species, including frogs, toads, salamanders, turtles, and snakes.

Bat Guidance

  • Caltrans Bat Mitigation: A Guide to Developing Feasible and Effective Solutions (PDF)
    This guidance document was developed to update the California Bat Mitigation Techniques, Solutions, and Effectiveness report that was prepared for Caltrans in 2004. It describes bat habitat relative to transportation structures, discusses bats’ conservation status, details the pertinent regulatory framework, and provides guidance for assessing bat habitat on highway infrastructure. This document describes how to identify and characterize potential temporary and permanent impacts on bats related to bridge and culvert projects, discusses mitigation strategies, and provides mitigation case studies and recommendations based on field assessments by expert bat biologists at 39 bridges and culverts with bat mitigation habitat incorporated into their designs. 

  • Caltrans Technical Guidance for the Assessment and Mitigation of the Effects of Traffic Noise and Road Construction Noise on Bats (PDF)
    This manual provides Department engineers, biologists, and consultants with guidance related to the effects of traffic noise and road construction noise on bats. This document covers the sound environment, bat hearing, echo location and communication, effects of highway noise on bats, and presents guidelines for project noise assessment and management. Literature citations and abstracts have been included in Appendix C and constitutes a significant portion of this document. The PDF format of this guidance allows the extensive citations to be easily searched.