Saturday, February 27, 2021

Crested Serpent Eagle

Crested Serpent Eagle Spilornis cheela (Latham) 1790
Other Name: Nil
Resident & Migrant
Author: Mr Terence Ang

Status and distribution
Occur south to Johore. Borneo Island occurs in both Sabah and Sarawak.

Subspecies Burmanicus is the only migratory subspecies recorded in P.Malaysia.

All subspecies in Borneo were residents.

The adult is mainly medium-sized and "full-crested" head—facial skin yellow distinctive to serpent eagle group. The crest is black with white marked. Naped and hind necked dark with whitish marking. Throat and cheek greyish, pale range to darker in color. The throat may appear brown in some individuals. 

Underpart brown with a spot where some may appear as elongated white spot: Upperpart, warm brown. Thigh at the time seems unmarked.

The upper part is mainly brown above. When the eagle is perched, look out for the black terminal band and the white subterminal band.

In-flight, underwing covert brown with heavy white spot. Flight feather with a white subterminal band and broad black trailing edge. Soar with U shape, and wing held upwards. The tail usually are seen well with a black terminal band and more overall white subterminal band

Juvenile. Whiter face and crest. Slight dark brown appears scaling on the crest. Upper part brown with white on the tip of the feather. Underpart white with streaking. Throat and breast all white.

Malayensis race is usually darker on the throat and may appear black. Dark variation typically points to these subspecies. The underpart of this subspecies was mainly dark, with usually darkest among all four subspecies.

White spots are also less heavily marked compare to burmanicus. Nevertheless, due to the darker color, it tends to make the white area more pronounced. Thighed usually appear white bar. Upperpart on shoulder spot white.

The juvenile below is mainly dark brown with plumage very near-adult. Leg colors are paler. Underpart more heavily spots to the thigh—shoulder of the bird's spots white. Crest tends to show more white.

Pallidus subspecies are very pale and restricted to north Borneo.

Richmodi breast is more rufous and unbarred with cheek and throat grey.

Juvenile of both Borneo subspecies are poorly document.

Confusion Species
Possible to confuse both the Oriental Honey Buzzards orientalis race and the torquatus race. From Honey-buzzard by Posture and jizz of bird are relatively different, the absence of erect crest and face skin was yellow. 

The underpart of the body with spots is somewhat distinctive to Crested Serpent Eagle. 

In Borneo's mountain area, such as Kinabalu, this species may be confused with the Kinabalu (Mountain) Serpent-Eagle, separated by the smaller, relatively shorter wing. It is also noted that pallidus subspecies are paler birds overall with cheek, throat, grey, and a larger white spot on the abdomen. Take note of the range and altitude. Mountain serpent eagle is restricted to montane.

Geographical Variation
Two subspecies were recorded in P. Malaysia

S.c.malayensis : resident

S.c.burmanicus : Migratory subspecies Both juvenile burmanicus have been confidently identified with two confirmed records, one in Kuala Selangor and another in Johore. Other adults were unconfirmed, and one adult observed suspected to burmanicus was also documented up north. Various records of adults restricted to lowland with no case pointed to Burmanicus subspecies were mention in montane.

In Borneo Island
S.c richmodi: Sarawak

Some texts have suggested that Natuna Serpent-Eagle Spilonis natunensis occur in Borneo; however, there was no evidence to support such claim.

Note: See above for a description

Observation on hunting and territorial display in Merapoh Taman Negara, Perak, Kuala Selangor, and Penang, in the lowland. On limited occasions, hunting was observed in the mountain area. A few successful observation was in the montane Genting Highland and Cameroon Highland. This was only limited to Malaysia, with two hunting occasions in Sabah and a few more on territorial display.

Territorial display
The majority of the time, observation on CSE calling in flight is on territorial display. Each time pair will fly together and calling. Where territorial meet with other groups, more pairs can be observed flying nearby, and all individuals can be observed calling. In one occasion in Merapoh Taman Negara, three pairs were observed, and all three couple was calling. Circling within their territory but never enter and no conflict arises. Observation in Sandakan in one of the projects yield the same result. Meanwhile, in the nesting period, female may be calling on perch, to communicate with the  male which is not territorial display. 

Hunting methodology was noted where CSE practices perching hunting method. As of date, almost 100% of all observations in the hunting process are perching hunting. There was no documentation of where soaring hunting was practiced. The bird mainly perches quietly motionless unless movement from the head. The prey will be detected from the flight, and once noticed, the CSE will fly directly to the quarry. Prey items are mainly reptile consisting of lizards such as garden fence lizard and snake, consisting of both venomous and non-venomous snakes such as Sumantra Spitting Cobra, Monocled Cobra, Bronzeback.

On one occasion, an observation was made on a mangrove where a crab was observed to be a prey item. (see photo attach)

Approaching the prey is mainly done in two types. Where non-venomous snakes and lizards are hunted, the CSE comes directly to the quarry and griping the snake or lizard directly during landing.

However, when approaching venomous snakes, the strategy has been switch differently. The prey is detected on perch. CSR will fly to the prey's side or very near the quarry but never snatch it directly. Once landed on the ground, the CSE will strategize occasionally opening its wing to attract the snake's attention. This will continue till the opportunity to attack the snake's head is available. The bird will directly attack the snake's head, killing it. If the bird is feeding, the snake will be brought to the nearby perch for feeding. For nesting birds, venomous snakes are often brought back with heads almost severed or been severed. 

Although with such great predator strategy, in Naroaji's book, it was noted that the death case of CSE due to snakebite had been documented. On my observation, however, I have yet to have such an encounter. Although some prey was observed to be a more challenging choice and more effort will be required.

It will be great to know from other observers in the country on this observation and share the knowledge available, which will be a great assistant to the habitat management program.

Cover various of habitat but usually wooded area up to 8000 feet asl.

Breeding records have been documented in the mangrove and montane area at approximately 4000 feet asl.

Only one egg and one eaglet was raised on all occasion and never recorded more than once. Observation on nest show medium size. 2 nests observed in mangrove was off covered well with leave and entrance were subjected to one entry. Nevertheless, this was different from the nest sighted in Fraser's Hill, where the medium-sized nest was located on a fork. This nest was relatively open and leaning on top of a bird's nest fern. All perch on lowland were not more than 10-15meter height. Fraser's Hill nest was an exception, with nest sighted at least 40 meters in height.  Females spend more time in the nest and caring for the eaglet while males conduct most hunting. 

There is not much evidence where Crested Serpent Eagle here reuse the nest; however individual sighted nesting over five years rebuilt new nest near the old one and approximately 50m radii from the original nest. This suggests that they may use the old nest described in many texts but will occasionally be built. 

Courtship display has seen birds were presenting stingray as early as in March. Nest with young in May. Fraser's Hill nest was also sighted in May. 

The dependency period of the young was somewhat challenging to document. One nestling was observed near the nest together with an adult six months after fledging. There is no evidence recorded locally where dependency period longer than six months.


Ben F.King & Edwards C.Dickson, 1989, A Field Guide To The Birds of South-East Asia, Collins, Grafton Street, London

Craig Robson, 2017, A Field Guide To The Birds of South-East Asia, Bloomsburry, London

Handbook to Birds of The World, Lynx Edicions, Bercolona, Collins, Grafton Street, London

Smythies B.E Revised by Davison G.W.H, 1999,  The Birds Of Borneo, Natural History Publication, Sabah Malaysia. (ISBN 983-812-028-6)

Susan Myers, 2009, A Field Guide To The Birds of Borneo, Talisman, Singapore

Boonsong Lekagul & Philip D.Round, 1991, A guide to the Birds of Thailand, Saha Karn Bhaet Co., Ltd Bangkok

David R Wells, 1999, Birds of The Thai Malay Peninsula Vol 1, Academic Press, London UK

James A. Eaton, Bas van Balen, Nick W. Brickle & Frank E. Rheindt, 2016,  Birds of the Indonesia Archipelago Greater Sundas and Wallacea, Lynx Edicion, Bercelona

James Fergusan Lee and David A Christie 2001, Raptors of The World, Christopher Helm, Great Britian (ISBN 0-618-12762-3)

Medway & David R Well 1976, The Birds of the Malay Peninsula Volume V: Conclusion and Survey of Every Species, Broadwaterpress, England

One observed feeding on crab

Juvenile of malayensis subspecies. Differ from juvenile Bumranicus white underpart with streak

In flight

Adult taking off

Adult malayensi subspecies with clear barred on thigh

Adult suspected to be Burmanicus subspecies. See the less marked white spot below and unmarked thigh

Subadult malayensis subspecies. Individual observed under 6 month dependency period