Crested Serpent-Eagle Spilornis cheela Scientific name definitions

50–74 cm (cheela), 50–56 cm (perplexus); 420–1800 g (palawanensis 688 g males, 853 g females 1 Gamauf, A., Preleuthner, M. and Winkler, H. (1998). Philippine birds of prey: interrelations among habitat, morphology, and behavior. Auk. 115(3): 713–726. Close ; pallidus 675–925 g); wingspan 109–169 cm (cheela), 110–123 cm (perplexus). Small to fairly large dark brownish eagle ; size extremely variable; shoulders and undersides (especially belly, thighs and undertail-coverts) variously marked with white spots or barring. Females average 4–6% larger than males, but up to 17% larger in some subspecies 2 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close . Short, rounded dark crest and broad wings characteristic; prominent pale band in tail and along trailing edge of underwing present distinctive pattern in flight. Juvenile paler with black face patches and two pale tailbands. Racial variation mainly in size and colour: nominate race largest, minimus smallest; island forms (e.g. <em>spilogaster</em> , <em>perplexus</em> ) tend to be smaller, some only half the size of nominate cheela; birds from wetter habitats (e.g. <em>abbotti</em> , bido) tend to be darker; ricketti averages larger than burmanicus, has paler underparts, narrow whitish bars on breast, and fewer bars/spots over rest of underparts. .

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Present in a wide variety of tropical and subtropical forest habitats, including dry to wet primary forest, riparian gallery forest, savanna, mangroves, degraded semi-open mixed forest, tea and teak plantations, and edges of cultivated areas and villages. Typically avoids dense forest interior; prefers secondary or partly open forest, clearings, gaps and forest edge. Preference for edge and more-open forest reflected by increased abundance with logging in SE Sabah on Borneo (7 Johns, A. G. (1996). Bird population persistence in Sabahan logging concessions. Biological Conservation 75(1):3–10. Close ). Home-range size of radio-tagged birds in Taiwan averaged 12·3 km² using minimum convex polygon method (8 Walther, B.A., Chou, T.-C. and Lee, P.-F. (2014). Population density, home range, and habitat use of Crested Serpent-Eagles (Spilornis cheela hoya) in southern Taiwan: using distance-based analysis and compositional analysis at different spatial scales. Journal of Raptor Research. 48(3): 195–209. Close ). Race perplexus of Ishigaki and Iriomote Is, Japan, unusual in favouring wet grassland habitat, in addition to forest edge (9 Ueta, M. and Minton, J.S. (1996). Habitat preference of Crested Serpent Eagles in southern Japan. Journal of Raptor Research. 30(2): 99–100. Close ). Occurs mostly from sea-level to 2000 m, occasionally as high as 3000 m or more in Bhutan and Nepal (10 Tymstra, R., Connop, S. and Tshering, C. (1997). Some bird observations from central Bhutan, May 1994. Forktail 12:49–60. Close , 2 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ).

Usually considered sedentary aside from juvenile dispersal, but birds that clearly were northbound migrants observed in S Thailand in Mar 2007 and 2008 11 DeCandido, R. and Nualsri, C. (2009). Timing and abundance of Grey-faced Buzzards Butastur indicus and other raptors on northbound migration in southern Thailand, spring 21511517–21511518. Forktail. 25: 90–95. Close .

Feeds mainly on reptiles, especially tree snakes ; less commonly on mammals, crabs, eels, frogs and birds. Recent study in India documented 173 prey items: 74% reptiles, 18% birds, 7% amphibians and 0·5% each fishes and mammals 12 Gokula, V. (2012). Breeding ecology of the Crested Serpent Eagle Spilornis cheela (Latham, 179159) (Aves: Accipitriformes: Accipitridae) in Kolli Hills, Tamil Nadu, India. Taprobanica. 4(2): 77–82. Close . Another study in India recorded predation on termites 13 Vasava, A. (2011). Crested Serpent-Eagle Spilornis cheela preying on termites (Termitidae) in Shoolpaneshwar Wildlife Sanctuary, Gujarat, India. Indian Birds. 7(2): 56. Close , and in Peninsular Malaysia has been observed hunting large earthworms 14 Shepherd, C.R. (2018). Observation of a Crested Serpent Eagle Spilornis cheela catching and eating worms on the ground in Peninsular Malaysia. BirdingASIA. 29: 90–91. Close . Hunts almost exclusively from exposed perch near open glade or along stream or forest edge; when foraging remains still for long periods while scanning for suitable prey items. Prey taken on ground or from trees, after short stoop, and consumed on ground or on elevated perch .

Fairly noisy, especially during aerial displays in breeding season; also vocalizes while perched. Most common call a loud, shrill “pi-pi-wheeeah-wheeah”  , the introductory notes often inaudible from a distance 2 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close . Much time spent soaring and calling throughout year.

Nesting chronology varies with locality, depending on elevation, latitude and timing of rainy season (laying mostly in dry season in N of range): Dec–Mar in S India; Feb–May in N India and Sri Lanka; Feb–Apr in Burma and Sumatra, Feb–Nov in Java; record of second brood in Jun in Burma. Nests 55–105 cm across, 10–30 cm deep; lined with grass and green leaves; built by pair 6–25 m above ground in large tree; often near clearing or stream. Sometimes breeds in old nests of other raptors, e.g. Gyps bengalensis and Nisaetus cirrhatus 15 Naoroji, R.K. (1994). Observations on the courtship, nesting and hunting behaviour of the Crested Serpent-eagle, Spilornis cheela. Journal of the Bombay Natural History Society. 91(2): 311–313. Close . Spectacular display flights include mutual soaring, undulations and threat display, with wings bowed upwards and head and tail raised; all accompanied by loud vocalizations. Clutch one egg (reports of two eggs should be verified); incubation c. 40 days (range 37–42 days), by female only; nestling period c. 64 days (range 59–65 days) 12 Gokula, V. (2012). Breeding ecology of the Crested Serpent Eagle Spilornis cheela (Latham, 179159) (Aves: Accipitriformes: Accipitridae) in Kolli Hills, Tamil Nadu, India. Taprobanica. 4(2): 77–82. Close . Hatchling has white down; both adults feed chick; post-fledging dependency period unknown. Fledgling seen being fed in Sept in Malaysia, suggesting a late nesting or long dependency period.

Not globally threatened (Least Concern). CITES II. Throughout extensive range generally widespread and common, sometimes abundant, but locally uncommon. No threats known at present, and species appears to be quite adaptable to habitat disturbance, including logging that opens up dense forest. Surveys are needed to determine conservation status of well-marked island races, especially because many (all?) may prove to be distinct species that would have small global ranges and population sizes. For example, race natunensis went completely unrecorded between 1937 and 2014, when it was observed several times on Belitung I in somewhat degraded habitat, and this taxon is suspected to be threatened by tin mining, loss of habitat (to explanding oil-palm plantations) and infrastructural development 16 Iqbal, M. (2015). Natuna Serpent Eagle Spilornis cheela natunensis: first photographic record in the wild. BirdingASIA. 24: 116–118. Close . Study of radio-tagged birds in S Taiwan found density of 2·7 individuals/km² 8 Walther, B.A., Chou, T.-C. and Lee, P.-F. (2014). Population density, home range, and habitat use of Crested Serpent-Eagles (Spilornis cheela hoya) in southern Taiwan: using distance-based analysis and compositional analysis at different spatial scales. Journal of Raptor Research. 48(3): 195–209. Close . Using average of only one pair/100 km² yields population estimate of 160,000–180,000 adults for all currently recognized subspecies 2 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close .