Eastern Spot-billed Duck Anas zonorhyncha 中華斑嘴鴨
Category I. Scarce winter visitor to Deep Bay area mainly in fresh and brackish water marsh; much declined from the mid-1990s, when it was common to abundant.
IDENTIFICATION
Nov. 2020, Kenneth Lam. Male (left), female.
58-63 cm. A large dabbling duck that has a bright yellow tip to the bill and is overall dark brown at rest with a pale head, white edges to the tertials and pale sides to the tail. The crown and nape are dark, while from bill base to behind the eye runs a dark eye stripe that contrasts with a pale supercilium. A dark bar from the bill base toward the eye varies in intensity and may be related to gender. Otherwise, females can only be distinguished by their smaller size and duller overall coloration.
Nov. 2017, Michelle and Peter Wong. Male.
In flight shows a bluish or greenish speculum (depending on the angle of view) bordered both sides by narrow white feather tips set against an otherwise plain brown upperwing. The underwing coverts are largely white. From head to the rear of the body gets increasingly dark.
VOCALISATIONS
The most commonly heard call is given by birds in flight when flushed.
DISTRIBUTION & HABITAT PREFERENCE
The majority of records are from the Deep Bay area, with rather few from elsewhere. Most have occurred on the ponds and gei wai of Mai Po NR, and more recently at the Lok Ma Chau MTRC Ecological Enhancement Area. Eastern Spot-billed Duck is rare on commercial fish ponds (though there is a count of 20 birds at Lut Chau on 28 November 2004) and on the intertidal mudflats.
Of the eight records away from the Deep Bay area up to 1998, two were of up to 31 zonorhyncha at Kam Tin, while the remainder (presumed to be this species, as there are no records of Indian Spot-billed Duck away from the Deep Bay area) were at Nam Chung/Luk Keng, Shuen Wan, Hebe Haven and Kai Tak between 29 October and 20 April. Since then, at Long Valley up to four have been recorded, while singles have been seen at Kam Tin and Pui O, Lantau.
OCCURRENCE
Although the data used for Figure 1 includes small numbers of Indian Spot-billed Duck prior to winter 1992-93, it is clear that from the mid-1980s to the mid-1990s Eastern Spot-billed Duck could be regarded as a common to abundant winter visitor, with the highest winter period count generally approximately 200 or more and the peak count being 511 on 13 January 1991. Although numbers prior to the mid-1980s were lower, it is likely this was a result of limited access to the Deep Bay area, including the intertidal areas.
Beginning in winter 1996/97 there occurred a substantial decline in the number of wintering birds, and since winter 2009-10 the peak winter period count has been fewer than 20 birds. It is now no more than a scarce to uncommon winter visitor.
A likely explanation for this remarkable change is that global heating has enabled the species to winter further north, as HK has always lain at the southern edge of its wintering range. A similar phenomenon has occurred for that other more northerly wintering duck Mallard.
Deciphering what has happened in the breeding season is more complicated due to the unrecorded presence of higher numbers of Indian Spot-billed Duck relative to the total population of the two species up to the mid-1990s. Leader (2006) found approximately equal numbers of pairs of each species in the breeding season around the turn of the century. Prior to 1995 there were regular double-figure counts in the breeding season (here defined as April to mid-August), the highest being 81 in the first week of July 1990. This suggests that though it is likely half of these birds were Indian Spot-billed Duck (assuming equal visibility of the two species at this time), the fact that since 1999 the highest breeding season count is 14 in 2020 indicates a decline in the breeding population.
During the late 1950s and 1960s there were records of up to 100 birds on evening flights and regular reports of flocks of up to 60 birds; in addition, there were hunters’ reports of ‘extraordinary numbers’ on 30 January 1960 causing them to run out of cartridges, and of 200-300 in August and September 1969. Furthermore, it was noted in the 1980s that there appeared to be greater numbers of birds in wing-moult at Mai Po during the autumn months. If these birds were from other parts of the Pearl River Estuary, it may be that rapid development of fish pond areas during the 1980s caused a local decline in numbers at that time.
Vaughan and Jones (1913) referred to Spot-billed Duck as the commonest of the ducks spending the winter in southeast China, with a few remaining throughout the summer and occasionally breeding. They also refer to a partiality for salt water, with which Herklots (1967) agreed. Macfarlane and Macdonald (1966) referred to flights over inland waters around Sai Kung. The brackish water of gei wai and fish ponds in the Deep Bay area remain the stronghold of this species, though there are no recent reports from Sai Kung of the kind of flights reported by Herklots.
Hybrid Mallard x Spot-billed Ducks are occasionally recorded and were described by Melville (1999).
BREEDING
Display has been noted in March and April, copulation in April and September and female Eastern Spot-billed Duck have been noted with chicks in April and May. However, although pairs have occasionally been noted in the breeding season from April to September, there is no substantial evidence this century of breeding having occurred.
Records of juveniles not assigned to either Eastern or Indian Spot-billed Duck have been received for dates from 6 May to 30 August.
BEHAVIOUR, FORAGING & DIET
No information, though its being rare in intertidal mudflats probably indicates it is vegetarian here as it is elsewhere (del Hoyo et al. 2020).
RANGE & SYSTEMATICS
Monotypic. Breeds from Lake Baikal southeast through eastern Mongolia to Ussuriland, southern Sakhalin, Hokkaido and northern China; it winters from Japan and the Korean peninsula to south China, including Taiwan, and northern Indochina (del Hoyo et al. 2020). In China breeds in northwest, northern and northeast areas and winters south of the lower reaches of the Yellow River; present all year in parts of the southwest east to the Pearl River Delta (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Figure 1.
Carey, G. J. and D. S. Melville (1996). Spot-billed Ducks in Hong Kong. Hong Kong Bird Report 1995: 224-230.
del Hoyo, J., N. Collar, and G. M. Kirwan (2020). Eastern Spot-billed Duck (Anas zonorhyncha), 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.spbduc.01
Leader, P. J. (2006). Sympatric breeding of two Spot-billed Duck Anas poecilorhyncha taxa in southern China. Bull. B.O.C. 2006 126(4): 248-251.
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.
Melville, D. S. (1998). Apparent Hybrid Mallard x Spot-billed Ducks. Hong Kong Bird Report 1997: 150-155.
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.
