Tawny Fish Owl: One Pair per Six Kilometers of Stream, a Nocturnal Raptor in a 1,800-Meter Michelia Tree

30-second overview: The Tawny Fish Owl (Ketupa flavipes) is Taiwan's largest owl. Its spread wings approach the height of an adult human; its toes are covered in yellow feathers, and the soles of its feet have spicules for gripping slippery prey. It was first recorded only in 1916 by the Japanese scholar Nagamichi Kuroda¹, and Taiwan's first precisely located breeding nest was not found until 1994². Sun Yuan-hsun's laboratory at National Pingtung University of Science and Technology has tracked it for thirty years. They found that a pair of Tawny Fish Owls needs 6.2 kilometers of stream, 44.6% surrounded by natural forest, to maintain a territory³. In April 2026, the research team found Taiwan's highest known nest in the hollow of an old Michelia compressa tree with a diameter at breast height of about 1.5 meters beside Qijiawan Creek in Wuling⁴. Shei-Pa National Park launched a 24-hour nestling livestream, giving the island its first chance to collectively see a strange raptor that is also one of its own.

One day in 1994, Sun Yuan-hsun found a nest in a tree beside Sakatang Stream in Taroko, Hualien. Bird's-nest fern is the largest epiphytic fern on this island; its thick feather-like fronds spread from the trunk in all directions, and the nest had been built in the middle of that clump of ferns. There was only one chick in the nest². When he returned to the tree, the chick's father had been shot by a hunter, and the mother had abandoned the nest. He brought the chick home, and his wife helped care for it. The young bird later failed to be released back into the wild and was sent to Taipei Zoo, where it was named "Heymei"⁵.

That was Taiwan's first precisely located Tawny Fish Owl breeding nest. Thirty years later, Sun Yuan-hsun's laboratory has tracked 91 territories, but precisely located nests still number in the single digits³⁶.

The Bird's-Nest Fern at Sakatang That Year

The Tawny Fish Owl entered Taiwan's ornithological history later than one might imagine. In 1916, the Japanese zoologist Nagamichi Kuroda first included it in Taiwan's list of resident birds¹. By then, Taiwan had been under Japanese rule for 21 years, and ornithology in the lowlands was already well developed. Yet the Tawny Fish Owl arrived so late that it was only "found" during the golden age of natural history. The reason is not complicated: it is nocturnal, inhabits little-visited stream valleys at low to mid elevations, has a low call and sparse territories, and is difficult even for professional observers to encounter.

By the early 1990s, Sun Yuan-hsun at National Pingtung University of Science and Technology had begun field tracking this bird along several streams on both sides of the Central Mountain Range: Wulai in Taipei, Sakatang in Hualien, and Wuling in Taichung⁷. Sakatang is part of the traditional territory of the Truku people; the 1994 discovery rewrote every coordinate that followed in Taiwan's Tawny Fish Owl research.

📝 Curator's Note
The name Heymei is a transliteration of Hedwig, the snowy owl in Harry Potter. From that 1994 rescue at Sakatang onward, the bird spent thirty years in the aviary at Taipei Zoo.

Sun Yuan-hsun and successive graduate students went on to publish a series of international papers on Sakatang and Wuling: a 1997 nest note from Sakatang in the Journal of Raptor Research², a 2006 food-habits study in the same journal⁸, and a 2013 Forktail paper on the spatial distribution of 91 territories³. The team learned many things over thirty years, but "seeing one with their own eyes" remained rare. According to interview records, members of the laboratory, who were said to "go up mountains and into water without regret," usually met this bird only by hearing the two-syllable duet of "guu—wu," seeing a silhouette under the infrared trigger of an automatic camera, or briefly locking eyes with it at the moment of release after banding⁷.

Mitten Crabs in the Pellets

The name "fish owl" is misleading.

A food-habits study conducted by Sun Yuan-hsun's team at Sakatang Stream from 1994 to 1999 found that stream fish certainly appeared in the Tawny Fish Owl's diet, including common species such as Opsariichthys pachycephalus, Taiwan shovel-jaw carp, and Taiwan white dace. But the largest biomass in the pellets was instead mitten crabs and toads⁸. The Taiwanese mitten crab (Eriocheir formosa), various freshwater stream crabs, and the Taiwan toad are large, slow-moving prey, and they were taken at frequencies clearly higher than their relative abundance in the environment. The researchers inferred that when streams flood and water levels rise, fish become harder to catch, so Tawny Fish Owls switch to catching mitten crabs and frogs in rock crevices along the banks⁸.

Their hunting method also differs from that of other large owls. Tawny Fish Owls have yellow feathers covering their toes, but rough spicules on the soles of their feet, which clamp firmly onto slippery fish and crabs. They share this adaptation with Southeast Asia's Brown Fish Owl and Buffy Fish Owl. The congeneric Blakiston's fish owl (Ketupa blakistoni) is distributed in the Russian Far East and Hokkaido, reaches 71 centimeters in length, and is the world's largest owl⁹. The Tawny Fish Owl is 48-61 centimeters long and weighs an average of 2,415 grams. It is Taiwan's largest owl, but only medium-sized within the fish-owl genus¹⁰.

💡 Did you know?
Among the world's 12 members of the genus Ketupa, only the Tawny Fish Owl has fully feathered toes. The other three fish owls, apart from the Brown Fish Owl, Buffy Fish Owl, and Blakiston's fish owl, have bare toes. Evolutionary biologists infer that this is related to the higher-elevation climate inhabited by the population distributed in Taiwan.

A Stream Not Poured in Concrete

The paper Sun Yuan-hsun's team published in volume 29 of Forktail in 2013 is the single most substantial study of Tawny Fish Owl habitat. They collected coordinates from 91 territories across Taiwan and used GIS to analyze environmental variables[^3]:

For readers outside ornithology, these numbers translate into everyday language like this: a 6- to 8-kilometer stretch of stream can support only one pair of Tawny Fish Owls. That stretch of stream must have no concrete embankments, no large-scale river engineering, and nearly half its banks still covered by natural forest. They do not use the surrounding plantation forests, makino bamboo groves, orchards, or villages³.

Territories on the west side of the Central Mountain Range have an average elevation 431 meters higher than those on the east side. The researchers inferred that because early logging and low-elevation development were more intense on the west side, Tawny Fish Owls were forced to retreat to higher remnant stream corridors³. In other words, the places where they can still breed today are themselves an inverse map of the destruction of Taiwan's mountain forests: where their nests remain, mid-elevation forests and streams have not yet been clear-cut or turned into concrete.

Shei-Pa National Park, Taroko National Park, and Yushan National Park, among Taiwan's largest protected areas, have become the last sites of stable Tawny Fish Owl populations¹¹. Many low-elevation stream populations outside national parks have already disappeared.

The Outline of a Dream Bird

In Taiwan's birdwatching circles, the Tawny Fish Owl is one of the few species called a "dream bird": nocturnal, identifiable only by a low two-syllable duet, restricted to remote stream valleys, and unseen even by many people who spend a lifetime birdwatching. In an in-depth report by the Taiwan Environmental Information Center, the researcher Sun Yuan-hsun described his laboratory this way:

"The reason they go up mountains and into water without regret is that the Tawny Fish Owl is cute and mysterious, like a lover."⁷

Most of the laboratory's work begins after midnight. They replay a recording of the "fish owl mother" call and wait for individuals in the territory to answer. This "playback" survey method was developed by Sun Yuan-hsun in the 1990s and later became a standard tool for nighttime raptor surveys in Taiwan¹². As technology advanced, the team added radio telemetry, automatic cameras, and satellite transmitters. In 2009, they successfully banded a female bird called "Sheng-jie" at Yousheng Creek in Wuling for the first time. Beginning in 2024, they installed two raptor perches at Qijiawan Creek, using automatic cameras to record a complete sequence of a Tawny Fish Owl catching a Taiwan white dace and bringing it back to a perch to eat¹³.

In May 2026, PTS Evening News produced a report describing this thirty-year research effort and Shei-Pa National Park's first 24-hour nestling livestream this year:

PTS Evening News report, 2026-05-03: Shei-Pa National Park's 24-hour livestream of Tawny Fish Owl nestling care fully recorded the process of parent birds caring for two chicks.

Heymei and Ailuo

Heymei, the chick brought home from Sakatang in 1994, entered the bird garden at Taipei Zoo. It lived there for more than twenty years.

For many years, the zoo's aviary tried to pair Heymei with another rescued individual, Ailuo. The problem was not unwillingness. Tawny Fish Owls form year-round pairs and are strongly territorial, and the two birds in the glass enclosure quickly established a bond. The problem lay in reproductive capacity: Heymei laid eggs every year, but almost none hatched. Until one year, they finally succeeded in raising offspring. These two birds, which would never have met again in the wild, accomplished in a glass enclosure what the wild population could not⁵.

Sun Yuan-hsun left another sentence in an interview, in the context of speaking about Heymei:

"This story may be a lesson in learning to let go."⁷

"Letting go" in this context means acknowledging that the 1994 rescue extended beyond a single bird. When the father was shot by a hunter and the mother abandoned the nest, rescue meant receiving the subsequent survival form of an injured family. Thirty years later, that pair in the glass enclosure proved one thing: conservation is not always about returning animals to their native habitat. Sometimes conservation means creating a new, sufficiently long home for individuals whose lives have been changed by accident.

The Michelia at 1,800 Meters

Beginning in 2024, Sun Yuan-hsun's student Hung Hsiao-yu took over leadership of the Qijiawan Creek project. In December 2025, he fitted a male bird with a satellite transmitter. In March 2026, the team discovered signs of breeding. On April 10, the nest was located in the hollow of an old Michelia compressa tree at about 1,800 meters above sea level, with a diameter at breast height of about 1.5 meters. It is Taiwan's highest known Tawny Fish Owl breeding record⁴.

Shei-Pa National Park seized the opportunity and launched the "Wuling Tawny Fish Owl Nestling Care" 24-hour YouTube livestream on April 29, 2026. The phrase "aerial nursery" appeared across major media. The livestream camera followed the two chicks, one 40 days old and 1,212 grams and the other 30 days old and 899 grams, as they peered out from the nest hollow, were fed by their parents, stretched their wings, and practiced flying. They were expected to leave the nest by mid-May[^4]:

The "Wuling Tawny Fish Owl Nestling Care" 24-hour livestream launched by Shei-Pa National Park on April 29, 2026. Inside the hollow of an old Michelia compressa beside Qijiawan Creek at about 1,800 meters above sea level, it follows the growth of two chicks, Dabao and Xiaobao. On May 1, 2026, the larger chick, "Dabao," successfully left the nest and moved to a branch above the tree hollow. The team immediately installed a second camera to track the chicks with a picture-in-picture view ¹⁴¹⁵.

✦ Taiwan's largest owl was named only in 1916; its first nest was found only in 1994; only in 2026 did the whole island see it together.

The livestream became a public topic across Taiwan, in a sense repairing the long-disconnected relationship between this bird and the island. Most people will never hear its call or see its silhouette in their lifetimes, but now anyone can open a phone and see, inside a Michelia hollow at 1,800 meters, two tawny chicks learning to spread their wings.

The Last Fortress of Giant Trees

The things Tawny Fish Owls need are very concrete, and all of them are disappearing from Taiwan's mountain forests:

1. Living trees or standing dead trees with a diameter at breast height of over 1 meter: only sufficiently old trees have natural hollows large enough. During the earlier era of mountain logging, most primary forest was felled; giant trees over 1 meter in diameter at breast height now remain only in national parks, protection forests, and Indigenous traditional territories¹⁶.
2. Streams that have not been concretized: embankment construction, wild-stream engineering, and reservoir impoundment have changed stream structure and sharply reduced fish resources.
3. Continuous belts of natural forest: 44.6% of a Tawny Fish Owl territory must be natural forest. Makino bamboo groves, plantation forests, and farmland do not count³.

Add the reproductive bottleneck, with an average of only one chick per brood, a 60-day nestling period, and extreme dependence on nest trees, and the fall of a single giant tree may break generational continuity in a population. In Taiwan's latest bird red list, released in 2024, the Tawny Fish Owl was assessed as Vulnerable (VU), even though the global IUCN assessment is only Least Concern (LC)¹⁷¹⁸.

There is also a kind of conflict that is less dramatic but continuously drains the population: among more than 100 cold-water aquaculture ponds across Taiwan, 25 have recorded Tawny Fish Owl predation, and 10 Tawny Fish Owls have drowned in ponds after entering fish farms¹⁹. Operators lose about NT$20,000-30,000 each year, a relatively small amount. Sun Yuan-hsun once suggested offsetting this through ecotourism, but few cases have been implemented.

⚠️ Contested View
What is the greatest long-term threat to the Tawny Fish Owl? Conservation discussions do not always give the same answer. Some say it is the scarcity of giant trees and natural tree hollows; others point to the concretization of streams; still others emphasize conflicts with fish farms and leg-hold traps. The three are actually different facets of the same thing: in Taiwan's modernization, the Tawny Fish Owl's home has been squeezed at once along three dimensions: habitat, food, and human tolerance. What needs protection is an entire ecology of "mountain streams not yet poured in concrete," and the Tawny Fish Owl is only one of the rarest residents within that ecology.

One Hundred and Ten Years

First named in 1916, first nest found in 1994, first fitted with a transmitter in 2009, and in 2026, the first satellite signal came from a Michelia hollow at 1,800 meters.

One hundred and ten years have passed. The people studying Tawny Fish Owls have changed generation after generation, and Taiwan's streams have grown shorter, straighter, and increasingly without the sounds of night. Yet every year, someone still walks into a stream valley after midnight carrying an infrared camera, waiting for a bird they have never been able to see completely clearly.

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

Further Reading:

• Formosan Ornithology — The Tawny Fish Owl was named only in 1916, one of the resident birds "discovered" by natural history only in the late Japanese colonial period; it reveals the temporal structure of ornithological research in Taiwan
• Formosan Landlocked Salmon — The two share the Qijiawan Creek ecosystem; in the same period, Sun Yuan-hsun was commissioned by Shei-Pa to study both species, two ends of the same habitat community
• Formosan Black Bear — Also a species long tracked by the Graduate Institute of Wildlife Conservation at National Pingtung University of Science and Technology; both depend on mid-elevation old-growth and giant-tree environments
• Taiwan Forest Ecosystems — With giant trees over 1 meter in diameter at breast height and the proportion of natural forest at stake, the Tawny Fish Owl is the most dramatic representative of "old-tree birds"
• Taiwan's National Parks — Shei-Pa, Taroko, and Yushan national parks are the last fortresses of stable Tawny Fish Owl populations, concrete examples of the protected-area system

References

Image Source

This article uses one CC-licensed image, cached under public/article-images/nature/ to avoid hotlinking 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