The Preference of Domestic Alien Toads, Bufo japonicus formosus, for Spawning Ponds on Sado Island

Although the global population of many native frog species has declined in recent years, alien frog species have spread rapidly worldwide. In order to eradicate alien frogs, characterizing their spawning sites is highly important. In recent years, eastern-Japanese common toads, Bufo japonicus formosus, have caused negative impacts on native ecosystems though predation and poisoning deaths as a domestic alien species. However, their spawning sites preference is little known. Here, to clarify when and what kind of ponds B. j. formosus prefers for spawning, we conducted a field survey on Sado Island which is one of the invaded regions of this species. We recorded their breeding season and analyzed what kind of ponds they use mainly focusing on the pond structure and landscape to obtain basic information for their eradication. Our results clarified that alien B. j. formosus on Sado Island have the same reproductive features as the native population according to the environmental conditions (lunar phase, wind speed, and rainless period), and the ponds they prefer for spawning are in areas with more surrounding forest and less rice paddy area regardless of pond structures. In addition, we identified that B. j. formosus on Sado Island currently have not yet formed large populations. These findings provide useful information for their eradication not only Sado Island but also in areas where B. j. formosus is distributed as an alien species. It is possibile that B. j. formosus on Sado Island can be eradicated completely if extermination activity is started immediately.

Automated summary

This study investigated the spawning habits of the eastern-Japanese common toad on Sado Island and found that they share reproductive characteristics with the native population. They prefer ponds with more surrounding forest and less rice paddy area for spawning, regardless of pond structure. Additionally, the population of B. j. formosus on Sado Island is currently small. These findings provide valuable information for the eradication of this alien species not only on Sado Island but also in other areas where it is distributed.