17 Years of monitoring show a 91% population decline in a common anuran in an otherwise stable amphibian community

Background/Question/Methods

Amphibians 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 employ an inexpensive and broadly applicable sampling protocol, and 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 short (5 – 15min) amphibian surveys and recorded the number of on-road amphibians along a single, 267 m stretch of secondary roads in rural Canada.

Results/Conclusions

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 are able to rule out a number of putative causes of the L. pipiens decline, but we cannot attribute a definitive mechanism to the decline. We hypothesize that it may be related to land-use change or infectious disease. Equally, our results show that a simple, temporally replicated road survey protocol, deployed in a spatially restricted area, can be as 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 citizen science initiatives.