Eastern Marsh Harrier Circus spilonotus 白腹鷂
Category I. Common winter visitor and passage migrant, most numerous in autumn. Mainly occurs in Deep Bay area wetlands.
IDENTIFICATION
Oct. 2014, Martin Hale. Juvenile.
47-55 cm. Medium-large raptor with long and broad rectangular wings that are often held slightly raised when gliding or soaring. Hunts flying low over reeds or marsh and swooping down on prey.
Females and juveniles, which predominate in HK, are rufous-tinged brown below with pale cream lower chest band that extends to the inner forewing, a dark upper chest band and rear face (variable in extent) and pale crown and throat. The underside of the primaries lack barring and are pale greyish with dark tips, broadest on the outers, while the secondaries are greyish, darker than the primaries. Juveniles have a dark iris and are dark rufous-brown above with a poorly-marked whitish rump.
Jan. 2023, Wellington Ngai. Adult female.
Eyes of the adult female are pale, and the pale rump is usually more obvious than on juveniles.
Dec. 2022, Paul Leader. Adult male.
Adult males have black outer primaries, greyish inner primaries, secondaries and greater coverts on the upperwing contrasting with dark mantle, forewing and head. From below the dark outer primaries contrast with the pale underwing and belly; the throat and chest are heavily streaked blackish.
Sep. 2022, Thailand. Ayuwat Jearwattanakanok. Immature male.
Immature males are separated from adult female Pied Harrier by lack of whitish shawl over forewing, lack of neat bars on upper side of inner primaries, plainer upper tail and less prominent facial disk (Ayuwat 2022).
VOCALISATIONS
A short ‘pseeeoo’ that rises and falls rapidly in pitch; can sound whistled or rather harsher and more gull-like.
DISTRIBUTION & HABITAT PREFERENCE
Most records are from the Deep Bay area and adjacent Kam Tin where birds are seen hunting over gei wai, fish ponds, reedbeds, mangroves and intertidal mudflats. Migrants are occasionally recorded elsewhere, mainly in autumn from 21 September to 14 November; there are three such spring records on 16 February and 14th and 18 April.
OCCURRENCE
Eastern Marsh Harrier is commonly seen in the Deep Bay area, particularly Mai Po NR, from October to March (Figure 1), with the main passage period in October and the first half of November. There appears to be a midwinter peak in January, which may reflect an influx related to chilly weather, or may in part be due to increased observer activity associated with the main winter waterbird count. Spring passage is evident from the middle of March. Extreme dates are 5 September 1981 and 9 May 1989.
Most reports are of immatures or females, with males accounting for only 2% of records since 1999; previously, this figure was estimated to be 7%, perhaps indicating that climate warming has allowed males to remain further north.
Records of Eastern Marsh Harrier usually concern one to four birds, but higher numbers can be present at winter roosts or during passage periods. Ten or more birds were noted at Mai Po on six dates in the winters of 1984-85, 1986-87 and 1988-89, and the highest count is 11 at Mai Po on 7 January 1989. Despite increased observer activity, only one count higher than six has been made since 1989, indicating that a decline, the reasons for which are unknown, may have taken place.
Formerly, La Touche (1931-34) considered that both Western Marsh Harrier C. aeruginosus and Eastern Marsh Harrier occurred in southern China, as did Herklots (1967) who also treated spilonotus as a subspecies of C. aeruginosus. However, all historical HK records are treated as spilonotus, as there is no evidence that aeruginosus occurs regularly in the region. However, birds showing characters of presumed hybrid spilonotus x aeruginosus are occasionally reported.
First reported in the Pearl River Delta area, and thus possibly HK, by Vaughan and Jones (1913) who regarded it as not uncommon in winter, Eastern Marsh Harrier was subsequently regularly recorded from September to April in the 1930s and 1950s, mainly in the Deep Bay marshes (Aylmer 1932, Dove and Goodhart 1955, Walker 1958).
BEHAVIOUR, FORAGING & DIET
The only food items reported are birds, those identified being a Grey Heron, thought to have been killed by an Eastern Imperial Eagle (Tipper 1992), Eurasian Wigeon (Carey 1998, Clarke 1999), Whimbrel, Black-headed Gull and a plover Charadrius sp. Usually seen quartering reed marsh or other wetland habitats at Mai Po NR.
RANGE & SYSTEMATICS
Monotypic. Breeds southeast Siberia, eastern Mongolia, northeast China, Ussuriland, Sakhalin and northern Japan, winters from South Korea and southern Japan south through south China and Indochina to southeast Asia, Sumatra and Borneo (Orta et al. 2020). In China a summer visitor to the northeast and a winter to the lowland southern half of the country (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Figure 1.
Aylmer, E. A. (1932). The birds of Hong Kong. Part IX. Order Accipitres (Falcons, Kites, Buzzards, Eagles, Hawks, etc.). Hong Kong Naturalist 3: 3-5.
Carey, G. J. (1998). Eastern Marsh Harrier drowning Mallard. Hong Kong Bird Report 1996: 171-172.
Clarke, R. (1999). Harriers drowning prey. Hong Kong Bird Report 1997: 158-159.
Dove, R. S. and H. J. Goodhart (1955). Field observations from the Colony of Hong Kong. Ibis 97: 311-340.
Herklots, G. A. C. (1967). Hong Kong Birds (2nd ed.). 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.
Orta, J., G. M. Kirwan, E. de Juana, and J. S. Marks (2020). Eastern Marsh-Harrier (Circus spilonotus), 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.easmah1.01
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.
Walker, F. J. (1958). Field observations on birds in the Colony of Hong Kong. Hong Kong Bird Watching Society, Hong Kong (duplicated).
