White-bellied Sea Eagle Haliaeetus leucogaster 白腹海鵰
Category I. Uncommon resident in coastal areas.
IDENTIFICATION
Feb. 2019, Michelle and Peter Wong. Adult.
75-85 cm. Adults are highly distinctive due to a combination of white underbody and lesser and median underwing coverts, dark grey upperparts and white tail.
Oct. 2015, Michelle and Peter Wong. Juvenile.
Juveniles are variegated brown and cream on the underwing coverts, have a largely brown body and blackish secondaries, inner primaries and tips to outer primaries contrasting with whitish primary bases. Immature birds gradually become paler below as they approach adulthood. Some may acquire a white tail with a broad black terminal band.
Nov. 2003, John and Jemi Holmes. Adult.
The bill is fairly deep, the head relatively small but the neck is long; the tail is short and wedge-shaped. Females are larger.
VOCALISATIONS
Displaying birds can be heard early in the breeding season, mainly from October to January. The calls are loud and slightly nasal, becoming faster when birds are in the air.
SYSTEMATICS & RANGE
Monotypic. Resident in coastal areas from western India east to southeast China and south through the Philippines, southeast Asia, the Greater and Lesser Sundas and Australia (Debus and Kirwan 2020). In China resident in coastal areas of south China, including Hainan and Taiwan (Liu and Chen 2020).
DISTRIBUTION & HABITAT PREFERENCE
Mainly recorded in coastal areas, with the known breeding locations extending from north and south Lantau to HK Island and eastern sea areas from the Ninepins north to Yeung Chau (Crooked Island) in Mirs Bay (So and Lee 2010). It is likely that the longer coastline and greater number of islands is a factor in the higher numbers in eastern areas.
Away from these areas, adults and young are irregularly reported in Victoria Harbour and Deep Bay, as well as at several of the larger reservoirs and occasionally at inland sites up to 10km from the coast.
OCCURRENCE
Most reports refer to one or two adults or immatures, but occasionally four to six are seen together. These usually comprise pairs in territorial disputes or display.
So and Lee (2010) estimated 15 breeding adult pairs in 2009, an increase from 23 adults in 2003. The number of immatures and juveniles was estimated by adding the number of fledglings produced in the previous five years and calculated to be 27, making a total maximum population of 57 birds in 2009. However, the actual population was stated to be probably lower due to mortality.
Vaughan and Jones (1913) first reported this species but did not find a nest site in HK. The number of breeding pairs increased from three in the 1930s and 1960s to ten in the 1980s and 1990s, most likely because of a decline in nest-robbing and disturbance by grass-cutters, which were significant problems in the past (Aylmer 1932, Taylor 1933), the eggs of this species reputedly being of value in traditional Chinese medicine (Herklots 1953).
BREEDING
Displaying adults have been reported from late September to mid-April. Nest-building has been observed from early October to early January. Incubation has been reported in the second half of December. The clutch usually consists of two eggs that hatch between early January and mid-March. The young may then remain in the nest for as long as 85 days, with fledging reported most often in March (Aylmer 1932, Taylor 1933, Dale 1965).
So and Lee (2010), as part of their investigation of the breeding ecology, reported a total of 15 territories across Hong Kong in the 2008/09 breeding season. Distances between territories ranged from 3.4 km to 18.7 km, a relatively dense distribution. Of the 15 territories, seven supported successful breeding pairs that produced eight fledglings. The long-term average number of active breeding pairs was reported to be nine pairs.
So and Lee (2010) noted that breeding success is variable and ranged from 14.3% of breeding pairs to 87.5%. The number of fledglings raised successfully ranged from one to ten (mean of five). Approximately 60% of the time only one of the two chicks survives. Factors cited as impacting breeding success were human disturbance, weather (colder weather causing lower breeding success) and habitat quality (pairs nesting in wooded habitats produced more young than those in more open habitats).
All nests reported by So and Lee (2010) were in natural habitats apart from a pair that nested in a cable tower at Tin Wan, Aberdeen. Most faced west, presumably due to northeast winds prevailing in the winter. Most nests were in living or dead trees, with one present on a rocky ledge and another on the ground. In contrast, the typical nest site reported in the 1930s was a rocky ledge, presumably due to the paucity of mature woodland habitat at the time. Nests may be used for several years, and refurbishment work may cause it to grow into a large structure up to two metres wide and 3.5 metres deep (Aylmer 1932, Taylor 1933, Dale 1965).
BEHAVIOUR, FORAGING & DIET
Food items identified from remains found at a nest in the winter of 1959-60 were cuttlefish, crustaceans and fish such as croaker, hairtail, puffer, moray eel and garfish. Other food items noted are ‘large Macao Crab’, skate and a sting ray (Taylor 1933), sea-snakes and carrion (Herklots 1967).
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Aylmer, E. A. (1932). The nest of the White-bellied Sea Eagle. Hong Kong Naturalist 3: 80-81.
Dale, C. (1965). The White-bellied Sea Eagles. Hong Kong Bird Report 1964: 34-36.
Debus, S. and G. M. Kirwan (2020). White-bellied Sea-Eagle (Haliaeetus leucogaster), 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.wbseag1.01
Dove, R. S. and H. J. Goodhart (1955). Field observations from the Colony of Hong Kong. Ibis 97: 311-340.
Herklots, G. A. C. (1953). Hong Kong Birds. South China Morning Post, Hong Kong.
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.
So, I. W. Y and W. H. Lee (2010). Breeding Ecology of White-bellied Sea Eagle (Haliaeetus leucogaster 白腹海鵰) in Hong Kong – A Review and Update. Hong Kong Biodiversity 18: 1-8.
Taylor, M. (1933). Further notes on the White-bellied Sea Eagle Haliaetus leucogaster. Hong Kong Naturalist 4: 11-12.
Vaughan, R. E. and K. H. Jones (1913). The birds of Hong Kong, Macao and the West River or Si Kiang in South-East China, with special reference to their nidification and seasonal movements. Ibis 1913: 17-76, 163-201, 351-384.
