Mountain serpent eagle  (Spilornis kinabaluensis)

The mountain serpent eagle is classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

The mountain serpent eagle (Spilornis kinabaluensis) is a fierce-looking, forest-dwelling eagle found only on the island of Borneo. A relatively small eagle, it has dark brown plumage that is paler and speckled on the underparts. The flight feathers of the long wings have black tips and white bases. The head and throat of the mountain serpent eagle are black with light speckles on the back of the neck (4), and it has a short, bushy crest of feathers on top of the head (5).

The long, dark tail of the mountain serpent eagle has a thick white band running across it, a feature that differentiates it from its close relative the crested serpent eagle (Spilornis cheela), which has a less distinctive greyish-white tail band. The mountain serpent eagle also has larger wings, smaller speckles and is generally darker in appearance than the crested serpent eagle (4).

Like all birds of prey, the mountain serpent eagle has an incredibly sharp, hooked beak, used for tearing apart its prey. The talons and beak are bright yellow and stand out against the dark body (6).

The call of the mountain serpent eagle is a repeated, high-pitched whistle (2).

The mountain serpent eagle is found only in Borneo. It is restricted to the mountains of central and northern Borneo, in Brunei, Malaysia and Indonesia (2).

An inhabitant of montane and submontane evergreen rainforest, the mountain serpent eagle favours ridge tops at elevations between 750 and 2,900 metres (2).

For many years the mountain serpent eagle was assumed to be a subspecies of the crested serpent eagle (Spilornis cheela), Borneo’s most common eagle (7) (8). Due to this, and the fact that its habitat is often difficult to access, little is known about the biology of this rare bird (6).

The mountain serpent eagle is often seen soaring over ridge tops (6). It has been reported to feed on snakes and lizards, including anglehead lizards (Gonocephalus species) (9).

Information on the breeding biology of the mountain serpent eagle is also scarce. In one case, adults were seen with two juvenile birds in November (9).

The greatest threats facing the mountain serpent eagle are habitat loss and degradation. This is mainly due to logging and the expansion and intensification of agriculture, forcing rainforest to be converted into oil palm, rice, maize, sugar and coffee crops (6).

However, because the mountain serpent eagle is found at high altitudes and in remote locations, it is secure in many parts of its range (6).

International trade in the mountain serpent eagle should be strictly controlled under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3). This bird is protected in Sarawak, and it occurs in Kinabalu Park in Sabah and Gunung Mulu National Park in Sarawak, where its habitat is protected (2) (9).

Outside of these parks there are no specific conservation measures in place for the mountain serpent eagle, as it is found at altitudes which are beyond logging and agricultural activities and is therefore assumed to be relatively secure in these parts of its range (2) (6). 

However, a number of conservation actions have been recommended for this species, including conducting research to accurately estimate its range and population, and to assess the degree of threat from habitat destruction. It is proposed that a large area of the mountain serpent eagle’s habitat in the Bornean highlands should be protected, and the areas that are currently protected should be properly managed (2) (6).

Find out more about the mountain serpent eagle and its conservation:

• BirdLife International - Mountain serpent eagle:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=3393

Find out about conservation in Borneo:

• WWF - Heart of Borneo Forests: 
  http://wwf.panda.org/what_we_do/where_we_work/borneo_forests
• Borneo Conservation Trust: 
  http://www.borneoconservationtrust.org.my/