Red-breasted Merganser Mergus serrator 紅胸秋沙鴨
Category I. Rare winter visitor, much declined since the mid-1990s.
IDENTIFICATION
Dec. 2012, Michelle and Peter Wong.
52-58 cm. Fairly large duck with a streamlined shape that is well-adapted for swimming underwater; long, narrow red bill, red eyes and short at times spiky crest on hind neck.
Adult female/immature birds have medium orange brown head and upper neck with diffusely bordered white throat, greyish underbody mottled darker on the sides, greyish-brown upperparts.
Dec. 2012, Michelle and Peter Wong.
In flight has slim profile; female/immature has large white patch on inner wing divided into two by black line, while male has larger patch separated into three sections. Both have largely pale inner half of underwing.
Adult male breeding has dark green head, white collar, black mottled brownish chest with large white spots at sides of upper flanks.
VOCALISATIONS
Generally silent away from the breeding grounds, and there are no reports of vocalisations heard in HK.
DISTRIBUTION & HABITAT PREFERENCE
Most records are from the Deep Bay area; previously there was a regular wintering flock along the section of coast from Tsim Bei Tsui to Nim Wan. Other records have occurred in widespread coastal waters. Observations from Po Toi have noted small numbers on northward migration in the second half of March.
There are only two records at enclosed inland water bodies: a male at Plover Cove Reservoir on 6 February 1982 and a female at Shing Mun Reservoir on 21 February 1993 (and probably also on 21 March and 4 April).
OCCURRENCE
A rare winter visitor and passage migrant that is much declined compared with the late 1980s and early 1990s when double-figure counts were made in most winter periods.
Up to 1998 Red-breasted Merganser was a somewhat irregular winter visitor to Deep Bay from the third week of November and a passage migrant there and in other coastal waters during spring to the end of March, rarely to mid-April (Carey et al. 2001). However, it was recorded in only nine winter periods from 1998-99 to 2013-14 and not at all from then to the end of 2020.
The highest count is 97 on 14 January 1990, while the mean peak count from 1985 to 1995 was 38. Migrating flocks of up to 27 birds were seen during the second half of March. In contrast, aside from a flock of eleven migrating northeast past Po Toi on 14 March 2009, all records this century have been of five birds or fewer.
The earliest on record occurred at Shuen Wan on 15 November 1999, though since then the earliest is 27 November. The latest record this century is five flying northeast on 30 March, while last century the latest records occurred on 12 April, with a further bird from 26 April to 4 May 1975.
Vaughan and Jones (1913) stated that Red-breasted Mergansers were common winter visitors to the Guangdong coast and were seen from 22 November to the end of April. Macfarlane and Macdonald (1966) stated there were no further records until December 1958, after when parties of up to 33 birds were frequently seen in Deep Bay between 7 December and the end of April.
BEHAVIOUR, FORAGING & DIET
Close-knit flocks foraging on fish were noted from Tsim Bei Tsui. Flocks of fast-flying migrating birds are occasionally seen in southern waters.
RANGE & SYSTEMATICS
Monotypic. Breeds across the Holarctic between 40oN and 75oN and winters coastally on both Pacific and Atlantic coasts of the U.S.A., in east Asia from Hokkaido south to southeast China and in scattered areas from northwest Europe southeast through the Black and Caspian Sea area to inland sites in Kazakhstan (Craik et al. 2020). In China a common winter visitor to coastal and nearby inland waters along the east coast, less numerous further south; a passage migrant through the northeast and there are scattered records inland as far as Xinjiang (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Carey, G. J., M. L. Chalmers, D. A. Diskin, P. R. Kennerley, P. J. Leader, M. R. Leven, R. W. Lewthwaite, D. S. Melville, M. Turnbull and L. Young (2001). The Avifauna of Hong Kong. Hong Kong Bird Watching Society, Hong Kong.
Craik, S., J. Pearce, and R. D. Titman (2020). Red-breasted Merganser (Mergus serrator), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.rebmer.01
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.
Macfarlane, A. M. and A. D. Macdonald, revised by Caunter, J. R. L. and A. M. Macfarlane (1966). An Annotated Check-list of the Birds of Hong Kong. Hong Kong Bird Watching Society, Hong Kong.
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.
