Predation of the Japanese Common Toad Bufo japonicus by Invasive Raccoons

抄録

Amphibians inhabit both aquatic and terrestrial environments and perform important ecological functions in each ecosystem. However, amphibian densities have been declining in recent years due to habitat degradation and loss, infectious diseases and climate change. In addition, predation by invasive raccoons (Procyon lotor) has recently become a concern globally. In this study, we evaluated impact of invasive raccoon to the Japanese common toad Bufo japonicus, which breeds briefly in early spring, over a five-year period to determine (1) the frequency of predation by raccoons using infra-red triggered camera traps, (2) whether the raccoon frequency differs before and after the breeding season of toads, and (3) the impact of raccoons on toad populations. We obtained clear video evidence of toad predation by raccoons over two years at a breeding site. Although it is necessary to investigate the decline in the toad population using more accurate methods, the maximum number of observed individuals decreased during the survey period. Furthermore, predation events exceeded 10 per breeding site per year. The frequency of raccoon appearances increased when toads began to breed. This suggests that raccoons selectively prey on toads aggregating in small ponds for breeding. The distribution of raccoons is expanding approximately 2.8-fold from 2007 to 2017 in Japan. Thus, there is an urgent need for toad conservation and raccoon control measures.