Hijijima Island Black-Legged Storm-Petrel Breeding Ground

An Island Where a Rare Seabird Returns Each May

Roughly 600 meters off the coast of Miyako City in Iwate Prefecture, a small uninhabited island rises from the Pacific. Steep striped cliffs of Cretaceous sandstone and conglomerate enclose it on every side, topped by a flat crown of broadleaf forest. The profile gave it the local nickname Gunkan-jima, or "Battleship Island." During the Naval Battle of Miyako Bay in 1869, vessels of the old shogunate are said to have mistaken its silhouette for a warship and opened fire.

The island is called Hideshima. Around 1.8 kilometers in circumference, with a maximum elevation of about 50 meters and a surface area of just 12,395 square meters, it is the largest island within Miyako city limits. It is also the only place in the western Pacific where the Band-rumped Storm Petrel (Hydrobates castro) is known to nest in numbers.

On December 24, 1935, the entire island was designated a National Natural Monument under the name Hideshima Kurokoshijiro-umitsubame Hanshokuchi, literally "the breeding ground of the Band-rumped Storm Petrel at Hideshima." Management was placed in the hands of Miyako City the following year. In 1982, the area was further designated as a national wildlife protection area, and the eight hectares enclosing the island became a Special Protection Zone where landing is strictly forbidden.

The Bird at the Heart of the Designation

The Band-rumped Storm Petrel is a small, soot-dark seabird with a narrow white band wrapping around the base of its tail. It spends almost all of its life over the open ocean, feeding on small fish, crustaceans, and squid skimmed from the surface as it flies. Land is something it visits only to breed, and only by night.

At Hideshima, the birds arrive in May. They excavate burrows close to one meter deep at the roots of red pines and broadleaf trees, or under the dense floor cover of yadake bamboo grass and oobajanohige (mondo grass). Each pair lays a single egg, sometime around July, and the parents take turns incubating it for thirty to forty-two days. The fledglings emerge from the burrows roughly two to three months later. By October the colony has dispersed back over the Pacific.

What makes the species remarkable is the scattering of its breeding sites across the planet. The other known colonies lie in the eastern Atlantic—Madeira, the Azores, the Canary Islands, Cape Verde—and in the tropical Pacific around the Galápagos and the Hawaiian Islands. Between those points stretch vast oceans without a single nesting site, except for this one small Japanese island. The disconnect is so striking that taxonomists now suspect "Band-rumped Storm Petrel" may in fact be a complex of several closely related species. The status of the Hideshima population within that complex remains an open scientific question.

Why the 1935 Designation Still Matters

Pre-war Japan was just beginning to formalize the protection of wildlife habitats, and the original 1935 record describes the site in characteristically terse prefectural prose: a place where the petrels burrow into the ground around July to nest and breed, and "a most uncommon thing as a breeding site." That brief language understates what is now clear from decades of follow-up survey work. Hideshima holds the only large-scale colony of Hydrobates castro in the entire western half of the Pacific basin.

The species is listed as Critically Endangered (CR) on Japan's Ministry of the Environment Red List. In 2019 it was further designated a National Endangered Species under the Act on Conservation of Endangered Species of Wild Fauna and Flora, restricting capture, trade, and disturbance. Only three breeding sites remain known anywhere in Japan, all of them along the Iwate coast.

The science behind the designation has deepened with time. Researchers from the Yamashina Institute for Ornithology began systematic burrow surveys at Hideshima in 1986. Their work, combined with monitoring by the Tohoku Regional Environment Office, has tracked the colony year by year through some difficult decades.

Pressures on a Small Colony

From the late 1980s onward, the Streaked Shearwater (Calonectris leucomelas), known in Japan as oomizunagidori, began nesting on Hideshima in rapidly increasing numbers. A much larger seabird, it digs its own burrows and tramples the forest floor in the process. Surface vegetation thinned out, especially the oobajanohige mats that storm petrels rely on for cover. Topsoil washed away. Tree roots became exposed. Storm petrel burrows were sometimes physically destroyed.

The 2011 Tōhoku earthquake and tsunami struck Hideshima with characteristic force, sweeping additional topsoil from the island and bringing down trees. Paradoxically, the disturbance briefly reduced the Streaked Shearwater population, and some forest-floor plants such as American pokeweed and giant knotweed began to return. The longer-term trajectory is still uncertain.

In response, conservation teams have buried metal grates and nest boxes across parts of the island. The grates are sized so storm petrels can pass through but the larger shearwaters cannot, creating refuges for the smaller species. The Yamashina Institute pioneered this technique in 1990; the Tohoku Regional Environment Office expanded it from 2017. Counts are still modest—five breeding pairs of Band-rumped Storm Petrels confirmed in nest boxes during a recent survey, against twenty-five for the larger Leach's Storm Petrel that also nests on the island—but the trend has stabilized.

Seeing the Island

Landing on Hideshima is prohibited year-round, and not just by convention. The entire island is a designated Special Protection Zone, and the ban is enforced. Even the conservation researchers who go ashore for surveys do so under permit, and only briefly during the breeding season.

What visitors can do is view the island from the water. The Miyako Umineko-maru, a pleasure boat operating out of Miyako Port, runs scheduled cruises along the rugged coastline north of the city and passes within sight of Hideshima. Smaller charter boats and sea kayaks, available from Sakiyama and the surrounding fishing villages, offer closer approaches in good weather. From the deck, the striped cliffs and the dense green crown of the island stand out clearly against the open Pacific. With binoculars, an attentive observer may catch the silhouettes of shearwaters returning at dusk; storm petrels themselves are nearly impossible to see from a distance, since they enter and leave the island only after dark.

The land-based viewpoint at Hideshima fishing port is also worth a stop. The village faces the island directly, and on a clear morning the sun rises behind it. The name Hi-de-shima, literally "the island where the sun comes up," is said to come from precisely that view.

What Else Is Nearby

Hideshima lies within the Sanriku Fukko (Reconstruction) National Park, established in 2013 from the older Rikuchu Kaigan National Park to integrate post-tsunami recovery with conservation along the northeastern coast. The same coastline is also designated as Sanriku Geopark, recognizing the geological record exposed in its cliffs. Hideshima itself is part of that record: the island's striped strata belong to the Miyako Group, a series of marine sediments laid down roughly 100 million years ago, in the Cretaceous. The rocks are famous among paleontologists. A schoolteacher who collected fossils on Hideshima in 1899 found ammonites, corals, and foraminifera typical of subtropical seas; sixty species were eventually described for the first time from the island, and fourteen of them carry the Latin epithet miyakoensis.

For travelers basing themselves in central Miyako, the Jōdogahama coastline a short drive south offers white pumice cliffs, calm coves, and well-marked walking paths through the same geopark. Northward along the cape lie Shiofukiana (a blowhole that erupts saltwater under heavy swell) and Rōsoku-iwa, the "Candle Rock," an isolated pinnacle of layered sandstone visible from the same boat tours that pass Hideshima. The Michinoku Coastal Trail, a long-distance hiking route running the length of the Tōhoku coast, passes through Sakiyama and offers walking-pace access to several of these viewpoints.