The camera switches on to a black and white video with a muffled click. It's 25 seconds long - just long enough to capture a tanuki, or raccoon dog as they're known in English outside of Japan, wandering up to a latrine site, crouching, and leaving a fresh sample for our lab. The time stamp indicates it's early in the morning.
A tanuki deposits a fecal sample at a latrine site in Seiburindo. At present, we have not developed a method to easily identify individuals, or males or females who are captured via camera trap at our study site.
About one hour later, the camera switches on and another tanuki is visible through the magic of night sensitive equipment - this time, the tanuki stands stock still next to the latrine, lifts its nose up into the air, sniffing deeply. Spending the better part of a decade in exotic animal husbandry makes me nervous about anthropomorphizing animals, but if I did in this moment, I'd imagine that he's thinking "Wow... she's beautiful!" before depositing his own sample in the latrine.
A tanuki sniffs the air before depositing its feces at a latrine site in Seiburindo forest.
The camera switches on 3 more times that night, with 5 tanuki visiting this single latrine and leaving fecal samples of various sizes for me to find the next morning.
Returning to Yakushima begins with the breathtaking site of the mountains, visible here from the Miyanoura ferry terminal.
The Seiburindo coastal forest is the site of primary interest for our study for now. This coastal forest is rich with endemic species and subspecies, and the impact of tanuki as an invasive on these sensitive species is poorly understood.
Most of my time is spent staring intently at the forest floor, looking for tanuki latrines. Whenever I remember to look up and take in the sight of the forest as a whole, I'm well rewarded with a reminder of just how special and beautiful, and how diverse Yakushima is.
Returning to Yakushima at the start of August for the continuation of the Tanuki Project - our study of the invasive raccoon dogs on the UNESCO World Heritage Island Yakushima - I found that 5 samples in a day was a good day as I wandered from latrine site to latrine site in Seiburindo. As my route grew with the discovery of more latrine sites in the area, the number of samples gradually increased. One month later however, the latrines saw an explosion of activity, with an uptick of samples left behing for me to collect. I was suddenly collecting 19,20, 25 samples in one day from the same latrines I had monitored for over four weeks. It's possible this change in behaviour is caused by the change of season, and the unique breeding behaviour associated with tanuki.
While the greenery of the island still indicates the presence of a hot summer, the change in behaviour in tanuki with the increase in scent marking at latrines potentially indicates that their pairing behaviour is aligned with mainland populations.
Tanuki are monogamous, and autumn is the season where males and females pair and forage together to prepare for the winter ahead, before breeding in the spring. Male competition has been described as non-violent, and based in scent marking. Previous literature by Ikeda 1984 describes number of scats in latrines as changing seasonally. This seasonal variation extends to preferred dietary items (including endangered sea turtles, as I'll discuss in my next post!), with different prey species targeted at different times of the year, and it also extends to parasite load.
The colourful and unmistakable elytra (wing covers) of these Japanese tiger beetles (Cicindela chinensis japonica) were a commonly found glistening in latrines of tanuki this summer, suggesting that they are potentially a popular seasonal prey item across Seiburindo. Samples from September superficially appeared to not contain tiger beetle elytra.
In other parts of their invasive range, previous research has suggested that tanuki are devastating for amphibian populations, particularly on island habitats. Species like this Japanese toad (Bufo japonicus) found on the island may be at increased risk of predation. Yakushima has five species of amphibian, including one endemic subspecies.
Sawagani, or the freshwater crabs of the genus Geothelphusa, are another common prey item of tanuki in both their native and introduced ranges. On Yakushima, an endemic species of sawagani has been identified, and may be at risk of predation by tanuki. Sawagani are also common hosts of zoonotic trematode parasites which can be transferred to tanuki, where they may be carried to new environments.
Considering the importance of seasonality in tanuki behaviour highlights the significance of our work in undertaking the first long term, multiseasonal study of tanuki on Yakushima.