A 91% decline in a common anuran in an otherwise stable amphibian community inferred from 17 years of rapid road surveys

Abstract

AbstractAmphibians are disproportionately represented among the many vertebrate taxa that are declining globally. Few long‐term studies of amphibians exist, especially in temperate climates, hindering our understanding of long‐term trends in amphibian communities, which may delay or prevent management action. Here, we develop and deploy an inexpensive monitoring method with potentially broad scientific and community uptake, ‘rapid road surveys’. We test whether this protocol is useful in understanding relative abundance in an amphibian community over a 17‐year period. From 2003 to 2019, we performed thousands of rapid (5–15 min) amphibian surveys and recorded the number of on‐road amphibians along a single, 267 m stretch of secondary roads in rural Canada. Assuming that on‐road occurrence reflects relative amphibian population sizes, we show that amphibians have declined by approximately 73% from 2003 to 2019. The decline was driven by a remarkable 91% decrease in the abundance of northern leopard frogs (Lithobates pipiens), the species comprising the most observation records, while all other species did not show a temporal trend. We cannot attribute a definitive mechanism to the L. pipiens decline. However, by ruling out a number of putative causes, we hypothesize that it may be related to land‐use change or infectious disease. Our results show that a simple, temporally replicated road survey protocol, deployed in a spatially restricted area, can be a valuable tool for conservation scientists to understand trends in abundance across an entire community. We discuss how these rapid road surveys are likely a viable option for future community science initiatives.