(USGS Research Proposal) Underpass Evaluation and Enhancement for Small Vertebrates and Invertebrates

Focus Area

Wildlife & Ecosystems


Natural Resources






1-2 years

Research Idea Scope

Background and Objectives Roads of different sizes, substrates, and traffic volumes have been shown to inhibit the movement of large mammals, small mammals, herpetofauna, and invertebrates (Brehme et al. 2013). If a road creates an impermeable barrier to animal movement, populations can become isolated or fragmented. Fragmented populations are more vulnerable to local extinctions and other negative effects from demographic and environmental stochasticity, as well as from increased inbreeding and genetic drift (see reviews by Trombulak and Frissel 2000, Foreman et al. 2003, Fahrig and Rytwinski 2009, Taylor and Goldingay. 2010). Wildlife underpasses are meant to facilitate safe wildlife movement between natural areas transected by major roads. To date, most studies have focused on large animal movement through road underpasses. Very little is known about how small vertebrates and invertebrates respond to these structures or if current underpasses facilitate their connectivity across roads. The Department of Transportation (DOT) currently recommends that structure be added to underpasses and overpasses to increase movement of wildlife (DOT 2011). Locally, the San Diego Monitoring and Management Program has developed a draft Connectivity Monitoring Strategic Plan (CMSP) which identified the importance of determining current connectivity for a suite of small animal species sensitive to fragmentation as well as to identify and inform adaptive management actions needed to maintain, restore, or improve connectivity between conserved NCCP core areas in San Diego County. Our study aims to assess both current connectivity and effects of adaptive management for movement of small terrestrial vertebrates and invertebrates through underpasses which connect habitats transected by highways and roads. The underpasses in the study are large, open structures that connect upland habitats. Our objectives are to first identify which groups of small vertebrates and invertebrates are currently using or avoiding these wildlife underpasses and understand how these behaviors may be predicted by life history characteristics. Secondly, we will determine if and how the addition of structure/cover (rock) leading up to and within the underpasses facilitates small animal movement. As a result, we will better understand the effects of underpasses and the addition of structure on the permeability of roads to small animal movements. The results of this study will be of great value to add to the current body of knowledge in road ecology, as well as to help inform adaptive management of road underpasses.

Urgency and Payoff

WORK PERFORMED TO DATE Six underpasses connecting natural upland habitats were chosen for the study. Our study is a Before-After Control-Impact (BACI) design (McDonald et al. 2000). To establish current baseline conditions, the area within the structure and in the adjacent habitat were monitored for small vertebrates (small mammals and herpetofauna) during the activity period from March to August, 2012. The method for detection was the use of motion detecting infrared cameras, specially set to detect small animals. From this, we will identify what species occur in the surrounding habitat and identify what species, if any, are moving through the existing underpasses. Structure was added to four of the six underpasses in the Fall of 2012, allowing approximately six months for animals to acclimate to the treatment before subsequent post-treatment monitoring (March to August 2013). Structure was in the form of stacked concrete blocks leading up to the underpass and along one inside wall. We created a strip of cover on one side and left the other side as open to facilitate movement of species with both open and closed microhabitat preferences (see Figure 1). WORK TO BE PERFORMED WITH THIS GRANT We conducted one year of baseline data collection (2012) and one year of experimental data collection (2013). These data bouts resulted in over 1.5 M photos. We developed an analytical program for managing photos and data generated. Our original funding covered about 70% of this work to date and USGS matched this so that we could complete this portion of the study. To date we have only analyzed about 40 K photos for vertebrates but we have not analyzed these for invertebrates. With the funding requested here we will run the cameras for an additional year (2014), to see if the use of the structures continues to increase over time, and then will have the funding for analyzing the rest of the 1.5 M photos already collected, and the additional photos we expect to generate in this third year of the study (~.75 M photos). We will also generate at least one manuscript from this work for publication in a peer reviewed journal.

Suggested By

John M. Taylor US Fish and Wildlife Service 760-322-2070

[email protected]