Crested Serpent Eagle (Spilornis cheela)

Introduction

The Crested Serpent Eagle (Spilornis cheela), known in Japan as Kanmuriwashi, represents a unique Ryukyu subspecies (S. c. perplexus) found only on Ishigaki and Iriomote. Therefore, Japan lists it as Critically Endangered (CR), designates it as a Domestic Rare Wildlife Species, and protects it as a Special Natural Monument.

Appearance

This is a compact, broad-winged raptor with a bold yellow face, legs, and cere. In addition, it shows a slight crest, heavily barred tail, and finely patterned underparts. Its clear, two-note whistle often echoes over fields and forest edges, revealing its presence.

Habitat & Distribution

The Ryukyu subspecies S. c. perplexus is endemic to the Yaeyama Islands, breeding only on Ishigaki and Iriomote. Typically, it inhabits lowland forests, forest margins, farmlands, and coastal woods. Moreover, it frequently perches on roadside trees or poles to scan for prey.

Where to See in Japan

On Ishigaki and Iriomote, drive slowly through farmland and forest-edge roads at dawn. Early in the morning, you have the best chance to see birds resting low on branches. However, stay inside your vehicle or observe from a distance—road collisions are one of their biggest threats.

Behavior

A patient sit-and-wait hunter, the eagle often perches quietly before swooping down on prey. Occasionally, it walks along the ground while foraging and adapts well to open edges. As a result, it is visible near roads—sadly also where accidents occur.

Diet

Though named for its fondness for snakes, this eagle’s diet also includes frogs, lizards, crabs, insects, and small birds or mammals. Interestingly, studies on Iriomote show it shares prey resources with the Iriomote cat but avoids direct competition through seasonal differences.

Reproduction

Breeding begins with nest building in late January; eggs are laid in early April, usually one per clutch. After about 45 days of incubation, chicks fledge in 50–70 days, becoming visible near forest edges as they learn to hunt.

Conservation

The Ryukyu population is legally protected as CR, Domestic Rare Wildlife, and Special Natural Monument (1972; upgraded in 1977). According to surveys from 2012–2021, 24–62 birds were found on Ishigaki and 38–66 on Iriomote in the non-breeding season, showing no clear increase. Unfortunately, traffic collisions remain a major cause of mortality—locals and visitors alike are urged to slow down in key habitats.

Author’s Impression

I once traveled to Ishigaki Island to see the Crested Serpent Eagle. Encounters were frequent, though most birds were perched far away. Early in the morning, however, I found several resting quietly on roadside trees — and, with a bit of luck, even came across a pair perched together.