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Wildlife of Mikurajima Island

The Streaked Shearwater, a Seabird Endemic to East Asia

The streaked shearwater is a migratory bird that breeds on Mikurashima Island. They hunt for fish in the ocean during the daytime and return to the forests at night. Streaked shearwaters strike a unique but clumsy figure as they climb the Castanopsis sieboldii trees. Mikurashima Island is the world’s largest breeding ground for the streaked shearwater. For this reason, Mikurashima Island is designated as an ecotourism destination in Tokyo, along with the Ogasawara Islands. Unfortunately, however, the population of stray cats descended from cats brought onto the island by humans has been increasing. These cats are a threat to the streaked shearwater and other endemic animal species that have evolved on the island.

The Streaked Shearwater

Lethe diana mikuraensis, a Butterfly with Distinctive Patches

Lethe diana mikuraensis is a butterfly said to be endemic to Mikurashima Island. It is considered a subspecies of the Diana treebrown (Lethe diana), and its distinctive feature is its color, which is a deeper brown than that of the Diana treebrowns living on the mainland of Japan. While the mainland Diana treebrowns have two or three distinct white patches on the tips of their forewings, the Lethe diana mikuraensis has only one distinct white patch, with one faint white patch below it. Patches other than the large patch are barely visible.

Lethe diana mikuraensis

Not-to-fly Stag beetle, Mikuramiyama stag beetle (Lucanus gamununs)

It is a stag beet only in Mikurashima island and Kozushima island. The body is small, mostly less than 35 mm(1.4 inches) in size. It is a family of the stag beetle, but can not fly. It crawls and moves on the ground. On Mikurashima island, stag beetles are walking on every island road, but often they are stepped on. In Mikurahama island, MikuraMiyama stag beetle is such an ordinary creature. Let's take care so that we can coexist as a familiar existence for a long time.


Indo-Pacific Bottlenose Dolphins in the Ocean Around Mikurashima Island

You can swim with Indo-Pacific bottlenose dolphins in the ocean around Mikurashima Island. More than 100 of these dolphins live near Mikurashima Island, and visitors can enjoy dolphin watching from April to October. You can watch dolphins from boats, from the shore, or while floating in the ocean in swim rings. If the dolphins are in a playful mood, you may even be able to observe them up close. Please note that there are rules for dolphin watching, which we ask our visitors to follow in order to maintain the friendship between dolphins and humans. Please follow these rules and be on your best manners when watching the dolphins.


Itajii Chinquapin (Castanopsis sieboldii), a Tree Representative of Mikurashima Island

The virgin forest of Mikurashima Island is home to one of the largest colonies of giant trees in Japan. Old giant trees are found everywhere in the forest. The largest tree on Mikurashima Island is an Itajii chinquapin (Castanopsis sieboldii) located in Nango. This tree, named Ojii, boasts a trunk circumference of about 14 meters (131 feet). Castanopsis sieboldii is an evergreen tree in the beech family. It is known for producing acorns, which were used as a source of food in the Jomon period (14,000-300 BCE), and for its current use as a source of bed logs for growing shiitake mushrooms. The tree’s overwhelming presence is thanks to its appearance, which makes it seem as though child trees are growing to support the parent tree in the center. These large trees are regarded as the guardian trees of Mikurashima Island.

Castanopsis sieboldii

Calanthe izu-insularis, a Fragrant Orchid

Calanthe izu-insularis blooms in early summer, earlier than other orchids. Hikers in the forests of Mikurashima Island often notice Calanthe izu-insularis because of its aroma. Many wild Calanthe izu-insularis flowers used to be found on Mikurashima Island. Unfortunately, however, as the popularity of Calanthe izu-insularis rose, people took an excessive number of plants from the mountains, leading to the near-extinction of wild Calanthe izu-insularis. A small number of surviving Calanthe izu-insularis plants continued to grow together in Ebine Park, where the original habitat was enclosed with fences to reproduce the Calanthe izu-insularis habitat of the natural forests.

Calanthe izu-insularis

Heloniopsis orientalis, an Alpine Plant

Heloniopsis orientalis is an alpine plant that blooms from April to May. On Mikurashima Island, the temperature rapidly drops at altitudes of about 500 meters (1,640 feet) above sea level, making it possible to observe alpine plants on the island. Many broad and line-shaped leaves grow from near the root and radiate in all directions in a disk-like pattern. The flower stems, with a height of 10 to 20 centimeters (about 4 to 8 inches) grow from the center of the disk of leaves, and the flowers bloom with their tips pointing sideways. The Japanese name, shoujoubakama, comes from the shoujou, a legendary creature from ancient China, as well as the fact that the overlapping leaves resemble hakama, wide trousers worn with kimono as a type of traditional Japanese clothing.

Heloniopsis orientalis


このページの担当は自然環境部 緑環境課 自然公園計画担当です。

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