There doesn't seem to be any concrete evidence about how and when tanuki were introduced to Yakushima, although Sato et al. published that they were likely introduced in the 1980's, with the first recorded sightings in the early 1990's. Even so, before their introduction to Yakushima, tanuki had already become established on another unique island in Japan - Chiburijima in the Oki Dozen Archipelago, a recognized UNESCO Geopark.
The ferry ride from Dogo, the largest of the Oki Islands, to Chiburijima, offers some spectacular views of the archipelago, highlighting why this region was designated as a Geopark.
The Oki Archipelago is composed of four main islands, Dogo, Nishinoshima, Nakanoshima and Chiburijima. Nishinoshima is famous for the spectacular formations on the Kuniga coast...
.. While Chiburijima is easily recognized by the towering red cliff, Seki Heki.
The introduction of tanuki to Chiburijima is seemingly much less murky - records from the 1940's describe the introduction of a breeding pair to the island as a gift. It seems the tanuki escaped their enclosure, and their numbers have since increased to - at least according to some estimates - several thousand. Like Yakushima, the impacts of their invasion however are poorly understood. How many tanuki really are there on Chiburjima? Does their presence impact the transmission and spread of parasites and diseases (a particular concern for the many livestock farmers of Chiburjima)? Is their diet impacting populations of native species, including and endemic or endangered populations? Are they competing with native small carnivores, like the Japanese weasel, for resources?
A tanuki drinks from a cattle watering station, prompting our research team to wonder how interactions between the tanuki and cattle might be fascilitating the spread of parasites and diseases.
Chiburijima is composed of rolling highlands, lowlying scrubland and some cedar plantation forests. There are also beaches, where endangered abalone and sazae snails, whose collection is controlled by the local fishery, may be being predated by tanuki.
Shimazujima is a very small island connected to Chiburijima by bridge. We were wondering if tanuki were crossing the bride to enter the island - and quickly came to the conclusion that they must be, given the large latrine we located right on the birdge! Can you spot it in this photo?
Thanks to the financial support from the Oki Islands UNESCO Geopark, we have launched a new branch of our invasive tanuki research to find out more! Our questions remain broadly the same fpor the two islands - we can't wait to start making comments on a comparison between the two islands - but Chiburijima is a different environment, and so, offers opportunities to trial different methodologies. Unlike our study site on Yakushima where the low-lying coastal forest has a canopy cover too dense for aerial observation of ground dwelling species, Chiburjima highlands offer a unique opportunity for us to bring out our infra-red drone mounted camera! We are hoping to be the first to use infra-red drone mounted technology to assess a tanuki population. Our pilot study was a success as we confirmed our camera could indeed identify tanuki on the landscape, even in darkness, up to 70 meters above the ground.
Andrew preparing to launch our drone in the Seki Heki region.
Kasia and Andrew observe the drone controller screen during an early morning drone flight.
A pair of tanuki were recorded crossing the terrain on Akahageyama. We were thrilled at the clarity of the features and how easily we could distinguish the tanuki rom the surrounding rocks and cattle. The challenge remains to master our surveying technique with the drone to create a meaningful survey to assess the population in the region.
Additionally, we were able to collect 243 fecal samples from 49 latrines that were identified so far across the island, to help us begin to identify the diversty of parasite species and dietary profiles of the tanuki here. We are certainly going to be busy in the lab for the next few months!
Andrew discovers our first latrine of the trip - as is tradition for the tanuki work!
Charlie proudly stands with the second latrine discovered on during our pilot study - on the locally iconic bridge connecting Chiburijima to Shimazujima. This latrine made us wonder what the local people think about the locations of some of the tanuki latrines...
The impacts of introduced tanuki may be far-reaching. Everything associated with their introduction has the potential to impact the local environment, including the latrines that they form. When I look at invertebrates using latrines as sources of food or shelter, I not only wonder about potential for parasite spread, but also the result of the subsidies these sites provide. Are certain invertebrate populations benefitting from the presence of tanuki? The questions are endless!
We invite you to follow our updates on OkiTan to learn more about how our project continuous to develop with our generous partners in the Oki Islands! Check back to our blog in 2024 for advancements in our research.
I can't possibly end this blog post without a humble - or should I say fungal - brag. Surveying for latrines offers many opportunities to interact closely with a landscape and observe things that may otherwise go unnoticed. I have been searching accross three continents to find birds nest fungus for years now, and was beside myself with glee to discover some on Chiburijima during a latrine survey on Mount Akahage. A perfect reward after a long day of hiking across the highlands!