Crested Serpent Eagle Spilornis cheela 蛇鵰
Category I. Present all year in forested habitat or adjacent areas. Some evidence of passage.
IDENTIFICATION
Feb. 2021, Martin Hale. Adult.
50-74 cm. Medium-large raptor with broad rounded wing tips that glides and soars on uplifted wings. Upperparts of the adult (illustrated) are mid brown with pale spots or tips to wing coverts. Flight feathers are darker with a slightly paler broad band across the middle; tail dark brown. The underparts are brown with white spotting on the flanks and belly; in flight, a distinctive broad pale band stretches from the body to the wing tips.
Oct. 2009, Kinni Ho. Juvenile.
In flight the juvenile underwings are pale with dark barring and a broad dark tip on the flight feathers, while the feathers of the ‘thigh’ are narrowly barred dark brown.
Nov. 2010, Michelle and Peter Wong. Adult.
On the adult the flat crown and small crest at the rear are blackish with white markings. The legs are greyish to yellowish and the cere is yellow.
Oct. 2009, Kinni Ho. Juvenile.
The juvenile is pale below with sparse brown streaks that are broadest on the chest and form a dark patch on the side of the neck. The upperparts are brown with pale tips to the wing coverts and darker barring on the flight feathers and tail. The cere is yellow, while the legs are greyish.
VOCALISATIONS
Mainly in spring and early summer but also in autumn its distinctive display call is heard over wooded areas, but also over the Deep Bay area and other lowland areas.
DISTRIBUTION & HABITAT PREFERENCE
The stronghold of Crested Serpent Eagle is forested areas in the New Territories, mostly north of a line from Tuen Mun to High Island Reservoir. Elsewhere, it is present on Lantau, particularly the western half, where the forest is more mature, but also above Mui Wo. Since 2009 it has been recorded more or less annually on HK Island, but usually there are only one or two records. Most of these have occurred in the period March to mid–May, suggestive of passage.
Crested Serpent Eagle was recorded in 6.9% of 1km squares during the 1993-96 breeding bird survey, declining to 4.9% in the 2016-19 survey. However, the declines appear to have occurred in forested areas, and so this may be an artefact. This is also suggested by the fact it was recorded in 3.4% of squares during the 2001-05 Winter Atlas but 4.2% of squares during the 2016-19 winter atlas. Occasionally birds are present in open or marshy areas in the non-breeding season.
OCCURRENCE
Crested Serpent Eagle is present throughout the year, although most reports occur from February to May and September to November (Figure 1). These are the periods when the species vocalises most, meaning that its occurrence is not as weighted toward migrants as this pattern suggests. Observer activity is substantially lower in the summer months, which may be a factor in the low number of detections at this time; however, observer activity midwinter is high, and so is not a significant factor in the low number of reports at that time.
Records of four birds over Crest Hill on 7 April 1996 (two of which flew east), one flying northwest over Tsim Bei Tsui with Grey-faced Buzzards on 12 April 1997, three flying northeast at Ta Kwu Ling on 18 April, six flying northeast over Lam Tsuen on 15 May, one near the border at Ta Kwu Ling on 25 September and eight immatures at Pak Nai on 22 October suggest that passage does occur. The highest count is ten birds over Chi Ma Wan on 24 March 2008, though most records are of one to four birds.
The first record was of one shot by a farmer in Lam Tsuen in early 1940 (Herklots 1940); the next records occurred in December 1955 and March-April 1957 (Walker 1958). However, it was not recorded annually until 1970 indicating it remained uncommon during this period. Since then, Crested Serpent Eagle has become a widespread if uncommon resident in HK. As the species was present in neighbouring areas of China (Mell 1922, La Touche 1931-34, Yen 1933-34) but did not colonise HK until relatively recently, this is presumably due to the maturation of woodland here.
BREEDING
Although Crested Serpent Eagle almost certainly breeds, there is no firm evidence. Aerial display flights in forested areas are frequently observed, daily at the certain times of year. On one occasion in late April one was seen carrying nesting material, but no nests have been found and there are no observations of dependent young.
BEHAVIOUR, FORAGING & DIET
Crested Serpent Eagle can be seen patrolling rocky hilltops in search of sunning snakes or perched over undisturbed marshy areas or grassy hillsides waiting for prey to appear. Fine days in spring and autumn often result in this species soaring and calling, often in pairs, above forested hilly areas.
Snakes, including Greater Green Snake Opheodrys major, are the primary food item reported; in addition, it has also been seen holding Asiatic Painted Frog Kaloula pulchra.
RANGE & SYSTEMATICS
Occurs from India east through Indochina to south China and south through southeast Asia to the Greater Sundas (Clark et al. 2020). In China it occurs in much of the area south of the Yangtze extending to Taiwan (Liu and Chen 2020).
S. c. ricketti occurs in north Vietnam and south China including Hong Kong. Twenty other subspecies are also recognised, most of them island forms, including on Hainan and Taiwan.
CONSERVATION STATUS
IUCN: Least Concern. Population stable.
Figure 1.
Clark, W. S., J. S. Marks, and G. M. Kirwan (2020). Crested Serpent-Eagle (Spilornis cheela), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.crseag1.01.
Herklots, G. A. C. (1940). Notes and Comments. Ornithology. Hong Kong Naturalist 10: 122-127.
La Touche, J. D. D. (1931-34). Handbook of the birds of Eastern China Vol. 2. Taylor and Francis, London.
Liu, Y. and Y. H. Chen (eds) (2020). The CNG Field Guide to the Birds of China (in Chinese). Hunan Science and Technology Publication House, Changsha.
Mell, R. (1922). Beitrage zur Fauna sinica. Archiv fur Naturgeschichte 88 (10): 1-100.
Walker, F. J. (1958). Field observations on birds in the Colony of Hong Kong. Hong Kong Bird Watching Society, Hong Kong (duplicated).
Yen, K. Y. (1933-34). Les oiseaux du Kwangsi (Chine). L’Oiseau et La Revue Francaise d’Ornithologie (NS) 3: 204-243, 615-638, 755-788; and 4: 24-51, 297-317, 489-507.
