Roadkill-Induced Extirpation of Largest Known Population of Pacific Newts (Taricha spp.) Requires Emergency Response

The Wildlife Society Conference 2025
Authors
Madison Morgan, Road Ecology Center, UC Davis
Shannon Lemieux, Road Ecology Center, UC Davis
Laura Morris, Road Ecology Center, UC Davis
Selena Cao, Road Ecology Center, UC Davis
Fraser Shilling, Road Ecology Center, UC Davis
Abstract

Volunteers recorded 7+ years of mass roadkill mortality of one of California’s largest known populations of Pacific newts (Taricha spp.) on Alma Bridge Road (ABR) in Santa Clara County. ABR bisects newt habitat and Lexington Reservoir breeding grounds, resulting in one of the highest-reported rates of amphibian roadkill (34,231 dead newts, 2018-2024). The number of road-killed newts per hour of volunteer effort has been significantly declining ~10%/year (P=0.045). Simple linear and multilinear regressions revealed no significant relationship between roadkill and traffic or precipitation, variables which can influence roadkill rates. A decline in roadkill without a change in external factors suggests a population decline, with our analysis suggesting a rapidly approaching population crash. Midpeninsula Regional Open Space District is collaborating with the County and AECOM to mitigate roadkill, proposing 1.2 miles of elevated roadway segments along the 4.1 miles of ABR, with estimated completion in 3+ years. If this strategy had been implemented between 2018-2024 with 100% effectiveness, it still would have resulted in 9,633 recordings of newt roadkill. The response to this ecological emergency lacks urgency, a factor crucial to preventing population extirpation. We stress the treatment of ecological emergencies as actual emergencies.