Amphibian mortality on roads: A case study in Santa Cruz long-toed salamander habitat

Background/Question/Methods

Vehicular traffic is responsible for the death of an estimated 1 million animals in the United States daily. Biologists are concerned that road mortality may be a significant factor threatening the Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum), a critically-endangered endemic amphibian found only in a very localized area of California. However, no studies have quantified the impact of road mortality on this species. To study this question, we collected data on roads in Santa Cruz County, California, during two A. m. croceum winter migratory seasons from 2011-2013. We surveyed for animals and the number of cars along three road transects that separated breeding ponds from upland habitat; two transects were adjacent to known A. m. croceumbreeding ponds and one was adjacent to a potential breeding pond. We estimated the likely number of animals killed on these roads and the role traffic levels played in mortality.

Results/Conclusions

During the course of the study, we found five different amphibian species in the A. m. croceum habitat. Of the 11 A. m. croceum found on the road transects, 64% were dead. Based on the length of the breeding season and other factors, I estimated 134 A. m. croceum were killed during migratory seasons 2011-2013. Analysis of vehicles/hour indicated that between 51% and 67% of cars traveling the roads adjacent to A. m. croceum habitat were not residents of the area, but were traveling the roads to avoid the near-by highway. Thus, at least 50% of travelers did not need to be on these roads with the potential to kill an endangered species. Based on these findings, I recommend that the California transportation and wildlife agencies work together to limit traffic in this sensitive area to residents only. In addition, educational signs and under-road systems to assist animal movement within migration corridors could also reduce mortality.