UNESCO’s new World Heritage Site included for its unique biodiversity
Although they make up only 0.5% of the total area of Japan, the Ryukyu Islands are home to more than 60% of all the bird species in Japan.
The islands are thought to have been separated from the mainland about 2-12 million years ago, leading to a very unique evolutionary path for many of the species living on there. There are nearly 2,000 of such species, including over 1,600 insects and 71 vertebrates. Possibly one of the most intriguing aspects is that over 80% of the frogs and other amphibians are found nowhere else in the world.
In addition, 144 of the islands' plants and animals are on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, representing 40% of all such species in Japan.
Okinawa Island is a globally important biodiversity hotspot with numerous rare endemic and threatened species. However, as with many island habitats, they are incredibly fragile to outside influences and invasive species.
The endangered Okinawa rail is flightless and an easy target for mangooses. Their current population is estimated at 720 birds, down from 1800 in 1986. Images credit: IWL.
The same story over and over again
Three endemic bird species, the flightless Okinawa rail, the Okinawa woodpecker, and the Okinawa robin, are found only in the Yanbaru region of the northern part of Okinawa Island. Similarly to New Zealand, there were no carnivorous mammals on Okinawa until 17 small Indian mongooses (listed by the IUCN as one of the 100 most dangerous invasive alien species in the world) were introduced to the southern part of Okinawa in 1910.
The small Indian mongoose was introduced to the island to combat populations of venomous snakes, such as habu pit vipers. Their venom is hemotoxic but the mortality rate in humans is less than 1%. Nevertheless, the bite of a habu snake can cause nausea, vomiting, severe pain, considerable tissue damage, hypotension and in some cases death.
As is the case with many well intentioned introductions, this measure backfired (not helped by the fact that habu pit vipers are nocturnal and mongoose are diurnal). The mongoose population rapidly expanded to rule freely over the entire island (and to many other parts of the world) with no natural predators.
Okinawa woodpecker (critically endangered) population is now estimated to be less than 600 individuals. Their main threat is loss of habitat. Image source: Wikimedia Commons.
The three endemic bird species were not able to defend themselves against such an active, intelligent and adaptable predator - fast forward to now, they are on the IUCN Red List of Threatened Species with the Okinawa rail being categorised as “Endangered”, the Okinawa woodpecker as “Critically Endangered”, and the Okinawa robin as “Near Threatened”.
Islands Wildlife Laboratories’ conservation efforts
The Islands Wildlife Laboratories are funded by the Japanese government and are part of a larger mongoose control project that began in the early 2000s in Yanbaru which saw control fences built in the southern region.
Over the years, we have regularly trapped, hunted and blocked mongooses to the point where the endemic species should be able to recover, says Saimon Tezuka-Waninge.
We now have three anti-mongoose fences that are the first line of defence for this World Heritage Site. The mongoose fences are crucial in slowing down their migration through the territories. There are hundreds of traps along the third and most recent fence, including 140 Goodnature traps, which slow down or completely stop the migration of mongoose species. Detection dogs help find traces of mongoose scat (carnivorous wild animal droppings), fur and dens to help focus subsequent hunting efforts.
We also conduct regular surveys of endemic species to see how well they are recovering in response to reduced mongoose populations.
Intensive capture and kill (including a variety of trapping solutions) operations have significantly reduced mongoose population densities. As a result, endemic bird populations are currently stable and will hopefully increase soon.
While predator control has been a key aspect, so has restoring the bird's forest habitat. Logging has ravaged the forest environment, and it has subsequently been suggested that mature trees of over 40 years are needed for the bird’s to thrive. With increasing environmental awareness and decreasing demand for timber, Yanbaru's logging area is rapidly decreasing, allowing for progressive restoration of their habitat.
A modified Goodnature trap enclosed in a wooden box designed to specifically control mangoose. Image credit: IWL.
Cross-collaboration and ongoing monitoring
As we are funded by the government, we submit monthly reports to the authorities on the progress and number of successful captures, as well as on future plans. Twice a year, we hold seminars and advisory meetings with experts from all over Japan to review our methods and discuss how to proceed and improve.
Of the 140 traps, half of them have surveillance cameras monitoring trapping activity. These cameras are equipped with a passive infrared sensor that takes pictures of animals as they pass the trap. This allows monitoring not only of mongooses but also of native animals.
We record cases of successful capture, as well as cases where a mongoose has been seen near or around the trap itself. We are currently working with an electronics company that is developing an AI that can analyse the images from all the cameras and determine exactly when a mongoose was seen. If this is done correctly, it will reduce the number of man-hours needed to review thousands of photos.
The Yanbaru forest in Okinawa. Image credit: IWL.
This forest belongs only to Yanbaru’s native species
Mongoose have disrupted the ecosystem of Yanbaru and had a severe impact on local biodiversity. To preserve and assist continued restoration of Yanbaru's fragile biodiversity, it is absolutely essential to continue trapping (and other) efforts to fully eradicate or control the population.
The local biodiversity is the living relic of the island. Each island endemic species is found only on that particular island in the whole world. Endemic species contribute to their individual ecosystems and are a crucial element of the habitat's biodiversity.
All species must work in harmony with their local environment to create a balance that can never be replicated and they all deserve a fighting chance.
Small Indian Mongoose caught by a field camera on Yanbaru. Image credit: Ebony Forest.
Facts about the Small Indian Mongoose (Herpestes auropunctatus)
• Mongooses eat small mammals, birds, reptiles, eggs, and occasionally fruit. A number of mongooses, especially those of the genus Herpestes, will attack and kill venomous snakes for food
• Mongooses are diurnal and rest at night under rocks or in hollows at the foot of trees
• Mongooses are solitary and their territory is between 3 and 9 ha
• Mongooses are good jumpers and can jump over an 80 cm high fence. However, they rarely climb trees in the wild.
• Although the lifespan of mongooses on Okinawa Island is not yet known, it is estimated at one to three years, five years at most in other areas.