Tawny Fish Owl: Six Kilometers per Pair, a Nocturnal Raptor on an 1,800-Meter Formosan Michelia

30-second overview: The tawny fish owl (Ketupa flavipes) is Taiwan's largest owl, with a wingspan approaching the height of an adult human. Its toes are covered in yellow feathers, and the soles of its feet have fleshy spiny tubercles for gripping slippery prey. It was first recorded in 1916 by Japanese scholar Kuroda Nagamichi¹, and the first precisely located breeding nest in Taiwan was not found until 1994². The laboratory of Sun Yuan-hsun at National Pingtung University of Science and Technology has tracked this species for thirty years—they discovered that a breeding pair of tawny fish owls requires a stream 6.2 kilometers long, with 44.6% of its banks surrounded by natural forest, to maintain a territory³. In April 2026, the research team found the highest-known nest in Taiwan, inside the cavity of a Formosan michelia old-growth tree on the banks of Cijiawan Stream in Wuling⁴. Shei-Pa National Park launched a 24-hour nesting livestream, giving the island its first opportunity to collectively witness one of its most familiar yet unknown raptors.

One day in 1994, Sun Yuan-hsun found a nest in a tree beside Sakatang Stream in Taroko, Hualien. The bird's-nest fern (Asplenium nidus)—the largest epiphytic fern on this island—spread its thick, feather-like fronds outward from the trunk in all directions, and the nest sat at the center of that fern cluster. Inside the nest was a single chick². By the time he returned to the tree, the chick's father had been shot by a hunter, and the mother had abandoned the nest. He took the chick home, and his wife helped care to it. Later, the attempt to release the young bird back into the wild failed, and it was sent to Taipei Zoo, where it was named "Hedwig"⁵.

That was the first precisely located tawny fish owl breeding nest in Taiwan. Thirty years later, Sun's laboratory has tracked 91 territories, but the number of precisely located nests remains in the single digits³⁶.

The Bird's-Nest Fern at Sakatang

The tawny fish owl was written into Taiwan's ornithological history later than one might expect. In 1916, Japanese zoologist Kuroda Nagamichi included it for the first time in a checklist of resident birds of Taiwan¹; by that point, Japanese colonial rule had lasted 21 years, ornithological work in the lowlands was already well developed, and yet the tawny fish owl arrived late to the golden age of natural history. The reason is not complicated: it is nocturnal, inhabits stream valleys at low-to-mid elevations where few people venture, and its calls are low-pitched with sparse territories—even professional observers rarely catch a glimpse.

By the early 1990s, Sun Yuan-hsun had begun field-tracking this species along streams on both sides of the Central Mountain Range—Wulai in New Taipei, Sakatang in Hualien, and Wuling in Taichung⁷. Sakatang lies within the traditional territory of the Truku people; the 1994 discovery there rewrote every subsequent coordinate of tawny fish owl research in Taiwan.

📝 Curator's note
The name "Hedwig" is a phonetic translation of Hedwig, the snow owl from the Harry Potter series. Since the 1994 Sakatang rescue, Hedwig spent thirty years in the bird house at Taipei Zoo.

Sun and his successive graduate students published a series of international papers from Sakatang and Wuling: a 1997 nest-site note in the Journal of Raptor Research², a 2006 dietary study in the same journal⁸, and a 2013 spatial-distribution paper covering 91 territories in Forktail³. The team learned a great deal over thirty years, but "seeing one with your own eyes" remained rare. According to interview records, members of the laboratory—who "never regretted going up mountains and into streams"—mostly encountered the species through hearing the duet of a mated pair's two-syllable "hoo—oo," catching an infrared-triggered silhouette on a camera trap, or getting a brief face-to-face moment during a banding release⁷.

Haircrabs in the Pellets

The name "fish owl" is misleading.

Dietary studies conducted by Sun's team at Sakatang Stream from 1994 to 1999 found that while stream fish were certainly on the menu—such as Opsariichthys pachycephalus, Zacco platypus, and Varicorhinus barbatulus as regular items—the largest biomass in the pellets actually came from haircrabs and toads⁸. The Taiwan freshwater crab (Eriocheir formosa), various stream-dwelling crabs, and the Taiwan brown toad (Bufo bankorensis)—large, slow-moving prey—were taken at frequencies significantly higher than their relative abundance in the environment. The researchers hypothesized that during floods and high water, when stream fish become harder to catch, tawny fish owls switch to hunting haircrabs and frogs in the rock crevices along the banks⁸.

Their hunting method also differs from other large owls. The tawny fish owl's toes are covered in yellow feathers, but the soles of its feet have rough, fleshy spiny tubercles—slippery fish and crabs are gripped firmly the moment they are seized, an adaptation shared with the brown fish owl and the Malay fish owl of Southeast Asia. The Blakiston's fish owl (Ketupa blakistoni), a congener found in the Russian Far East and Hokkaido, measures 71 cm in length and is the world's largest owl⁹; the tawny fish owl, at 48–61 cm and an average weight of 2,415 grams, is Taiwan's largest owl but only medium-sized within the fish-owl genus¹⁰.

💡 Did you know?
Among the 12 species in the genus Ketupa, only the tawny fish owl has its toes fully feathered. The other species (except the brown fish owl, Malay fish owl, and Blakiston's fish owl) have bare toes. Evolutionary biologists hypothesize this is related to the higher-altitude climate of the Taiwanese population.

A Stretch of River Not Yet Lined with Concrete

The 2013 paper published by Sun's team in Forktail volume 29 is the single most comprehensive study of tawny fish owl habitat. They collected coordinates from 91 territories across Taiwan and analyzed environmental variables using GIS[^3]:

For readers outside ornithology, these numbers translate into everyday language as follows: a stretch of river 6 to 8 kilometers long can support only one pair of tawny fish owls. And that stretch must have no concrete embankments, no large-scale channelization, and nearly half of its banks must still be lined with natural forest. The surrounding plantations, bamboo groves, orchards, and villages are not used by the owls³.

Territories on the western side of the Central Mountain Range averaged 431 meters higher in elevation than those on the eastern side. The researchers hypothesized that because of earlier logging and more intensive low-elevation development on the western side, tawny fish owls were forced to retreat to higher-elevation stream refugia³. In other words, the places where they can still breed are themselves an inverse map of Taiwan's mountain-forest destruction: wherever their nests still exist, there remain mid-elevation forests and streams that have not yet been clear-cut or lined with concrete.

Shei-Pa National Park, Taroko National Park, and Yushan National Park—the three largest protected areas—have become the last strongholds of stable tawny fish owl populations¹¹. Many low-elevation stream populations outside the national parks have already been extirpated.

The Outline of a Phantom Bird

In Taiwan's birding community, the tawny fish owl is one of the few species called a "phantom bird" (夢幻鳥): nocturnal, with low-pitched, hard-to-distinguish two-syllable duets, inhabiting only remote stream valleys—even a lifetime birder may never see one. Researcher Sun Yuan-hsun described his laboratory in a feature article for the Environmental Information Center:

"What keeps them going up mountains and into streams without regret is the tawny fish owl's adorable, mysterious nature—like a lover."⁷

Most of the laboratory's work unfolds after midnight. They play back recordings of a "mother fish owl" call, waiting for a territorial individual to respond—a "playback" survey method developed by Sun in the 1990s that later became the standard tool for nocturnal raptor surveys in Taiwan¹². As technology evolved, the team added radio telemetry, camera traps, and satellite transmitters: in 2009, they successfully banded a female nicknamed "Sister Sheng" on Yousheng Stream in Wuling; starting in 2024, two raptor perches were installed along Cijiawan Stream, with camera traps recording a complete sequence of a tawny fish owl catching Varicorhinus barbatulus and carrying it back to the perch to eat¹³.

In May 2026, PTS Evening News produced a report on this three-decade research effort and Shei-Pa National Park's first-ever 24-hour nesting livestream:

PTS Evening News 2026-05-03 report: Shei-Pa National Park 24-hour livestream of tawny fish owl nesting, fully documenting the process of parent birds caring for 2 chicks.

Hedwig and Ailuo

The 1994 Sakatang chick that was taken home—Hedwig—entered the bird house at Taipei Zoo. It lived there for more than twenty years.

The zoo's bird house long attempted to pair Hedwig with another rescued individual, Ailuo. The problem was not unwillingness—tawny fish owls pair year-round and are strongly territorial, and the two birds in the glass enclosure quickly established a bond. The problem lay in reproductive capacity: Hedwig laid eggs every year, but almost none hatched. Then one year, they finally succeeded in raising offspring; the pair, who would never have met in the wild, accomplished in a glass enclosure what the wild population could not⁵

Sun left behind another quote in an interview, spoken in the context of Hedwig:

"This story may be teaching us the lesson of letting go."⁷

"Letting go" in this context means acknowledging that the scope of the 1994 rescue extended beyond a single bird. When the father was shot by a hunter and the mother abandoned the nest, the rescue became a way of catching the aftermath of a wounded family. Thirty years later, that pair in the glass enclosure proved one thing: conservation does not always mean returning an animal to its native habitat. Sometimes conservation means building a new, long-enough home for a life that was accidentally altered.

The Formosan Michelia at 1,800 Meters

Starting in 2024, Sun's student Hung Hsiao-yu took over leadership of the Cijiawan Stream project. In December 2025, he fitted a male with a satellite transmitter; in March 2026, the team detected signs of breeding; on April 10, the nest was located inside the cavity of a Formosan michelia old-growth tree at approximately 1,800 meters elevation, with a breast-height diameter of roughly 1.5 meters—the highest-altitude tawny fish owl breeding record ever documented in Taiwan⁴.

Shei-Pa National Park seized this opportunity, launching a 24-hour YouTube livestream titled "Wuling Tawny Fish Owl Nesting" on April 29, 2026. The phrase "sky nursery" made headlines across major media outlets. The livestream camera followed two chicks (40 days old, 1,212 g; 30 days old, 899 g) as they poked their heads out of the nest cavity, were fed by the parents, and stretched their wings in flight practice, with fledging expected by mid-May[^4]:

Shei-Pa National Park's "Wuling Tawny Fish Owl Nesting" 24-hour livestream, launched April 29, 2026. Inside a Formosan michelia old-growth tree cavity on the banks of Cijiawan Stream at approximately 1,800 meters elevation, the growth process of two chicks.

✦ Taiwan's largest owl, not named until 1916; the first nest not found until 1994; not seen collectively by the entire island until 2026.

The livestream became a national phenomenon in Taiwan, in a sense reconnecting the long-broken relationship between this bird and the island. Most people will never hear its call or glimpse its silhouette in their lifetime, but now everyone can open their phone and watch two tawny-brown chicks learning to spread their wings inside a Formosan michelia tree cavity at 1,800 meters.

The Last Fortress of the Giant Trees

What the tawny fish owl needs is specific, and all of it is disappearing from Taiwan's mountain forests:

1. Living or standing dead trees with a breast-height diameter of 1 meter or more: Only sufficiently old trees have natural cavities large enough. The era of mountain logging removed most old-growth forest; today, trees with a breast-height diameter exceeding 1 meter survive only within national parks, protection forests, and indigenous traditional territories¹⁴.
2. Streams not lined with concrete: Embankment construction, mountain stream channelization, and reservoir impoundment have altered stream structure and drastically reduced stream fish resources.
3. Continuous natural forest cover: A tawny fish owl territory requires 44.6% natural forest; bamboo plantations, timber plantations, and agricultural clearings do not count³.

Combined with reproductive constraints—an average of only one chick per brood, a 60-day nestling period, and extreme dependence on nest trees—the fall of a single giant tree can sever a population's lineage. The tawny fish owl was assessed as Vulnerable (VU) in Taiwan's 2024 updated Red List of Birds, even though the global IUCN assessment is only Least Concern (LC)¹⁵¹⁶.

There is also a conflict that is less dramatic but steadily eroding the population: across more than 100 cold-water fish farms in Taiwan, 25 have recorded tawny fish owl predation, and 10 owls have drowned after entering fish ponds¹⁷. Annual losses to operators are approximately NT$20,000–30,000—relatively small in scale. Sun once suggested offsetting losses through ecotourism, but few cases have been implemented.

⚠️ Contested perspective
What is the greatest long-term threat to the tawny fish owl? The conservation community does not always agree on the same answer. Some point to the scarcity of giant trees and natural cavities; others highlight stream channelization with concrete; still others emphasize fish-farm conflicts and leg-hold traps. These are in fact different facets of the same thing: in the course of Taiwan's modernization, the tawny fish owl's home has been squeezed simultaneously along three dimensions—habitat, food, and human tolerance. What needs protecting is an entire stretch of "mountain stream ecosystem not yet lined with concrete," and the tawny fish owl is only one of the rarest residents of that ecosystem.

One hundred and ten years

First named in 1916, first nest found in 1994, first transmitter attached in 2009, first satellite signal transmitted from a Formosan michelia tree cavity at 1,800 meters in 2026.

One hundred and ten years. The people studying tawny fish owls have changed generation after generation. Taiwan's streams have grown shorter, straighter, and quieter at night. But every year, there are still people who walk into stream valleys after midnight with infrared cameras, waiting for a bird they have never been able to fully see.

And now, on a Formosan michelia at 1,800 meters, two chicks are learning to spread their wings.

Further reading:

• Ornithology of Formosa — The tawny fish owl was not named until 1916, one of the resident birds "discovered" by natural history only in the late Japanese colonial period, revealing the temporal structure of ornithological research in Taiwan
• Formosan landlocked salmon — The two species share the Cijiawan Stream ecosystem; Sun was commissioned by Shei-Pa to study both simultaneously, two ends of the same habitat community
• Formosan black bear — Also a species long tracked by the Institute of Wildlife Conservation at NPUST, both dependent on mid-elevation old-growth tree environments
• Taiwan forest ecosystems — With trees of 1-meter-plus breast-height diameter and natural forest proportions, the tawny fish owl is the most dramatic ambassador of "old-growth forest birds"
• Taiwan's national parks — Shei-Pa, Taroko, and Yushan National Parks are the last strongholds of stable tawny fish owl populations, a concrete case of the protected-area system

References

Image Credits

This article uses 1 CC-licensed image, cached in public/article-images/nature/ to avoid hotlinking to the source server:

• Tawny fish owl. _Ketupa flavipes_ - Flickr - gailhampshire — Photo: gailhampshire (Cradley, Malvern, UK), 2009-02-17, CC BY 2.0 via Wikimedia Commons