Since the winter of 2018, thousands of Pacific newts, including California newts (Taricha torosa) and rough-skinned newts (Taricha granulosa) have been recorded dead on Alma Bridge Road in Santa Clara County, California. Alma Bridge Road is a part-time recreation access and commuting road that bisects the largest known population of Pacific newts’ upland forest habitat and breeding grounds in the Lexington Reservoir. This bisection results in one of the world’s highest-reported rates of amphibian roadkill each rainy season. Large-scale migration of amphibians during rainy seasons is common, including across busy roads. Volunteers who first brought the mass roadkill to the attention of the county in 2017 have noticed that the number of dead newts recorded each rainy season is decreasing. Using volunteer observations of 34,231 dead newts from 2018-2024, a simple linear regression was performed between total newt carcasses and year. The number of road-killed newts per hour of volunteer effort has been significantly declining at a rate of ~10%/year since 2018 (P=0.045). Simple linear and multilinear regressions revealed that there was no statistically significant relationship between carcasses observed in a season and traffic or precipitation, both of which can influence newt roadkill rates. There also was no significant change in survey effort. A decline in roadkill usually indicates a proportional decline in population size if environmental factors and traffic rates stay the same. While one modeling study has predicted that the population will face extirpation in as few as 50 years, our analyses suggests that the population may be rapidly approaching a crash.

Midpeninsula Regional Open Space is currently working with Santa Clara County and AECOM, an environmental consulting company, to mitigate newt roadkill in hopes of preventing local extirpation. The likeliest of proposed mitigation includes 1.2 miles of elevated roadway segments along the 4.1 miles of Alma Bridge Road. It will not be completed for at least three more years. If this mitigation strategy were to be 100% effective, it would have still resulted in 9,633 recorded instances of newt roadkill from 2018-2024. Other less-costly mitigation measures could be taken immediately to ensure the high rate of newt mortality is met with sufficient response, such as limiting traffic to residents only during rainy periods when newts are migrating.

We propose that a 10+ year timeline (2017 to after 2027) from recognition of the problem to construction that focuses on less than 30% of the roadway where mortality occurs may be a typical transportation agency response, but is not an appropriate response to rapid population extirpation. We suggest a new way of thinking where ecological emergencies because of roadways are treated like transportation emergencies (such as landslides) and met with a rapid and effective response, such as traffic control.