Friday, June 22, 2018

The Squeakquel: Japanese squirrels and Formosan Squirrels in Kanagawa Prefecture

Squirrels are small. One of my senior Forest Instructors is a registered hunter for Kanagawa Hunting Club. He said under Japanese jurisdiction standard gun for hunting is shotguns. Hunters then choose bullets according to a game. The smallest 410A is inevitably for the smallest animals. “These days, it’s made of iron, not lead, in order to avoid any possibility of poisoning after use.” “Wow, is that so?” One day, he happened to shoot a squirrel with 410A and “It exploded to pieces! That was the stupidest thing I’ve done while hunting!” Oh my … Imagining the last moment of that tiny creature was … really sad … They are petit and lovely, aren’t they? Hm, well, one kind of them are causing a trouble these days in Yokohama and the south-east of Kanagawa Prefecture.

Table Manner of Japanese squirrel

Japan has three endemic squirrels, Japanese squirrel (Sciurus lis), Japanese giant flying squirrel (Petaurista leucogenys), and Japanese dwarf flying squirrel (Pteromys momonga). I’ll report you my experience with 2 airborne squirrels later this summer. Today is related to Japanese squirrel. They live in the forests of not-so-high mountains of Honshu 本州 and Shikoku 四国 Islands. (Hokkaido 北海道 has Hokkaido squirrel and Hokkaido chipmunk both of which are in the families of squirrels in Siberia.) According to Wikipedia, an adult weighs about 250-300g with busy winter ears, changes fur color of their back between summer (red-brown) and winter (grayish white), and eats while its flowing tail is neatly positioned on its back. Japanese squirrels are semi-vegetarian with nuts, seeds, and occasional insects. Fortunately, they are not yet on the red list of endangered species for Japan. In Kanagawa Prefecture, their home is in Tanzawa 丹沢 and Hakone 箱根. So far, so good, right? It sounds it’s difficult to meet squirrels in the parks of downtown, doesn’t it? Now you visit or live in cities of Kanagawa Prefecture, like Yokohama or Kamakura 鎌倉. You have a relaxing weekend walk in a forest surrounded by houses, or sanctuary of ancient temples. And you may have a glimpse of small but long-tailed creatures hopping between the boughs. Squirrels! Cute! Not so fast, please.

Last month, I’ve been to Nagano Prefecture,
 and found lots of pine cones with food prints of Japanese squirrel.
When a Japanese squirrel finishes all the pine nuts from a cone,
 its food print is this.
 We call it “shrimp fritters.”
 They can regularly be found in the mountains of Kanagawa Prefecture.

In Japanese forests these days, there live the other kinds of squirrels too. For example, families of Siberian chipmunk and Eurasian red squirrel were first imported after the 1970s as pets or exhibition animals. They escaped from their captivity. Their Japanese habitat is still limited now, but National Institute of Environmental Studies listed them as “invasive” as they can compete with Japanese squirrel or Japanese dormouse. Moreover, there is an already established villain in Japanese forests. They are Formosan squirrel which first escaped to the wild of Oshima Island 大島 in 1935. Since then, they multiplied to dominate the island’s forest, gnawed electrical wires, and ate fruits of camellias that are for camellia oil which is the main ag-product of the their economy. In the early 1950s, Formosan squirrels were started to appear in the forests of the City of Kamakura. People said they escaped from Samuel Cocking Garden of Enoshima 江の島 (; do you remember we’ve visited there last summer in “Battle of Sexes”?) where the commercial garden raised them for tourists’ attraction. Since then, they are appearing in the forests of tourism spots near population centers. What Japanese government is anxious is the possibility of repeating British experience where Eastern grey squirrel imported during the 19th century are driving island’s squirrel into extinction and influencing the decrease in population of wild birds, like dusky thrushes, woodpeckers, and European jays. Formosan squirrel is listed in Invasive Alien Species Act and prohibited now to be imported, transported or raised in Japan. And Kanagawa prefecture, especially the south of Yokohama, Kamakura, and Miura Peninsula 三浦半島, is on the frontline of the problem.

Formosan squirrel in Segami Citizen Forest

Formosan squirrels are bigger than Japanese native. Adult weighs 300-400g with gray-brown fur which doesn’t change seasonally. They were from Asian tropical rain forests where lots of fruits are available year-round. The easy access to food and always hot temperature made them bigger and fecund. They can produce 1-3 pups whenever. From conception to pup’s leaving the nest, it’s only 80 days, and a female becomes an adult within a year. But rich ecosystem of the tropics provides many kinds of predators that keep the population of Formosan squirrel in check. In contrast, Japan has 4 seasons. Especially during winter to spring, the forests are freezing cold. Probably because of this, Formosan squirrels in Japan produce pups only 1-2 times per year. The availability of fruits in winter-spring forests is strictly limited for relatively large squirrels. But, hey, next to the Yokohama Citizen Forest is urban ag-lands for veggies of humans. In addition, this larger mammal throws away highly nutritious foods whenever (and wherever) convenient. They can even give squirrel foods in the garden of Tsurugaoka Hachiman Shrine 鶴岡八幡宮, in return for a “cute selfie together” as a memory of visiting Kamakura. Finally, forests around the megalopolis Tokyo do not have many raptors, large snakes, or wild mammals, as in tropical rain forests. i.e. Safe. The Formosan squirrels in Kanagawa are now like nuclear families in Yokohama or Kamakura. Although they have fewer babies than in their ancestral land, they nurture the pups in a protected, or artificial, environment, by commuting to food spots, and let their kids grow large. The population of adult Formosan squirrels has exploded. After first spotted in wild in the 1950s, they become common in Kamakura during the 1980s, and at the turn of the 21st century they are regulars in the Yokohama’s South Forests, like Maioka 舞岡, Segami 瀬上, Kanazawa 金沢, Hitorizawa 氷取沢, Kamariya 釜利谷, and Nature Observation Forest. That is the problem for humans.

In cold Japanese forest, Formosan squirrels build a nest
 with tightly knit twigs to keep inside warm.
 I think this is one of their houses,
 found in Yokohama Nature Observation Forest.
 They are rather too large for crows and look dense.
 It’s easier to find them during fall to winter
 when the trees shed the leaves.

First, commercial farmers in the east Kanagawa Prefecture found themselves as victims of meals for squirrels. Producing winter vegetables is a lucrative business in the suburb of Tokyo. Yokohama is one of the nation’s biggest producing areas for Japanese mustard spinach, a popular winter green. Such veggies are also liked by squirrels in winter. Citruses, persimmons, grapes … orchards for such fruits which could provide nice income during winter holidays attract lots of hopping and munching squirrels during cold weather. Then, the other incidences emerged. When Formosan squirrels cannot find meal during winter, they start licking saps by stripping the barks off from the trees like camellia, Machilus thunbergii, Japanese zelkova, and maple. Substantial pealing from a tree during winter = gardling is a standard procedure for forest thinning. The citizen forests and the other protected areas in the south-east Kanagawa are now having a possible deterioration of the forest due to the squirrels. The worst case scenario is, Formosan squirrels cross Sagami River 相模川 and enter Tanzawa and Hakone where Japanese squirrels live. There, the similar story of Britain with Eastern grey squirrel can come. Formosan squirrels may win over the Japanese squirrels and the other animals and birds for food, and could destroy trees that already have problems with deer. The municipalities of Yokohama, Kamakura, Yokosuka, Miura, Zushi, and Hayama Town have special budget for controlling the squirrel population to stop such things to happen. Controlling? Yes, they use mousetrap to capture, euthanizing by CO2, and incinerating them as industrial garbage. Yuk.

This camellia at the entrance of Enkaisan Hiking Course is
 literally eaten alive by Formosan squirrels.
 Could you see a particular kind of scars on its trunk?
 That’s the sign.
Here is another.
 It’s Machilus thunbergii in Yokohama Nature Observation Forest.
 Both camellia and Machilus thunbergii could
 withstand the attack of squirrels up to a point.
 In contrast, those trees which shed their old barks en masse,
 such as Japanese zelkova and maple,
 react to gnawing of squirrels with
 substantial falling of their skin,
 and often die easily.

All in all, it’s a typical tale of unintended consequences born out of careless action of humans. Formosan squirrels did not come to Japan by their own decision, but ended up stranded. One ranger for Yokohama Nature Observation Forest is sanguine. “Well, if there is nothing to eat, it’s natural for squirrels to chew anything useful for survival, isn’t it?” Yeah … besides, in the suburban forest of Yokohama or Kamakura, they are certainly substantial and cute mammal that we hikers can meet relatively easily. Er, well, if you plan to have a selfie with Formosan squirrel in Japan, please visit the large shrines and temples in Kamakura. The squirrels there are a sort of city squirrels very relaxed to be fed by food from tourists. They positively come near you begging something to eat. If you oblige their request, the animals will give you a chance to have a photo with them in return. Quid pro quo. Clever … but … at least those which hopping between the trees in the citizen forests of Yokohama, they are more cautious and moving rapidly high above the heads of us hikers. Not only shaking boughs of trees, Formosan squirrels in the forest are also barking in the woods. In tropical rain forests, when they realize a snake is approaching to swallow their pups, they call each other with a voice similar to sparrow but in more urgent, thicker, and louder way to call for collective defense. For approaching raptors, their voice becomes similar to short-circuited cry of angry crows to let their fellow to stop moving and to become invisible from the above. When a larger mammal predator is coming from the ground, they really bark like a dog, in a very low voice to signal the others to escape higher of trees. If you walk in Yokohama’s South Forests, and hear something like bird’s call, but it sounds more robust, that’s the voice of squirrels. One day, I was welcomed by such dog-like barking from the above near the visitor center of Nature Observation Forest. Squirrel! So, mean Naomi was doing circles around the tree where the voice came from. As I enjoy my leisurely circling, the call got more and more rapid and hysteric, or neurotic, I would say.

 “Gwow, gwow, gwow, gwow, gwow!!!!!!!!!!!!!!”

Hmmmm. Naomi did not have any plan to capture you to incinerate … though you may not know … The city life of Formosan squirrel is not easy in Yokohama in the end, I guess.

If you find a problem in the South Forest of Yokohama, please make a contact with

Office for the Park Greeneries in the South 南部公園緑地事務所
Yokohama Municipal Government Creative Environment Policy Bureau 横浜市環境創造局
Phone: 045-831-8484 (I guess in Japanese only)
FAX: 045-831-9389 (I hope there is somebody who can read English …)

Yokohama Nature Observation Center at Yokohama Nature Sanctuary
Phone: 045-894-7484

FAX: 045-894-8892 

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