Lesser Black-backed Gull Larus fuscus 烏灰銀鷗
Category I. Abundant winter visitor and passage migrant in early spring to Deep Bay and southern coastal waters; low numbers at other times.
IDENTIFICATION
Mar. 2010, Michelle and Peter Wong.
51-61 cm. Medium-dark grey upperparts, greyish head streaks before the spring moult and yellow or predominantly yellow legs identify adults in HK. Although adult / near adult Slaty-backed Gull has equally dark (usually darker) upperparts, they are rare in HK and differ structurally. Primary moult of adult Lesser Black-backed Gulls is later than other large gulls, and in HK most complete in the last week of February or, as in the case of this bird, the first half of March.
A minority of birds appear to be hybrids with Vega Gull. These show intermediate structure, plumage and/or moult; leg colour varies from yellow through pinkish-yellow to pink.
Mar. 2009, Thomas Chan.
Adults usually have extensive black in the outermost three primaries (P8-P10), one white ‘mirror’ on the outermost primary, with that on P9, if present, usually small. Note contrast in shade of grey on inner wing and mantle compared with outer wing, due to difference in angle of light. Leg and bill colour (orange-tinged yellow) are typical of adults in early spring. The outermost primary is full-grown indicating moult is complete (date 12 March).
Mar. 2010, Michelle and Peter Wong.
Compared to other large gull species on the HK List, identification of first-year birds relies on smaller size, slimmer body, longer wings and smaller bill, the lack of contrastingly paler inner primaries, broad blackish tail band, dark greater coverts and gradual replacement of solidly dark juvenile mantle and scapulars by greyish-tinged feathers with dark subterminal band and pale fringe. The tertials are rather plain brown with only a pale fringe. Bill pattern varies from largely dark early in the winter to only having a dark tip later, while the head and chest can be contrastingly pale later in the winter.
Second-winter birds have dark grey mantle, scapulars and wing coverts, while third-winter birds also have grey primaries usually with a small white spot near the tip of the outermost primary.
Mar. 2012, Geoff Carey.
First-winter birds in flight have a tail band broader than that of Vega Gull but narrower than Slaty-backed Gull, often with dense barring at the base and a cleaner rump and uppertail coverts. The inner primaries have a poorly marked inner primary window, while the head often looks pale compared to the dark bill and upper mantle and neck.
VOCALISATIONS
Calls of European birds are said to be similar to Herring Gull L. argentatus but on average deeper and more nasal (Mullarney et al. 1999).
DISTRIBUTION & HABITAT PREFERENCE
Most records are from the roost that forms on the falling tide in Inner Deep Bay, but it is also seen in coastal areas. Flocks of birds are seen on northward migration over the sea, mainly in the vicinity of Po Toi, from 6 January to 12 April, with the highest counts occurring from the last week of February to the middle of March. The peak count of such birds is 291 on 15 March 2007. Perhaps the most unusual record is that of approximately 750 birds on 5 March 2016 in Mirs Bay, a location for which there are very few records.
OCCURRENCE
The default large gull species in HK forming the bulk of the wintering flock. The highest count is of 865 birds on 28 January 2000, with an additional 73 adults present the following day. Figure 1 indicates that peak winter counts are somewhat variable, which may be partly due to factors other than the number of birds present (i.e., height of tide on the date of any count). However, it appears that since winter 2015/16 numbers have been relatively low, with no count exceeding 350. The mean of peak counts in the five winter periods from 2016/17 is 265, whereas for much of the earlier period from 1985/86 (when access to the intertidal areas of Deep Bay was much improved due to installation of a boardwalk hide) this figure was generally above 400. Based on winter waterbird counts in Deep Bay Sung et al. (2021) concluded that the wintering population declined from 1998 to 2017.
Passage has generally ceased by the second week of April, though stragglers may remain to late May, the latest of these occurring on 27th. There is one summer record of a bird seen from 24 July to 10 August 2014. The earliest date on which return passage has been noted is 25 August 2018, though no more than five have been noted before 12 November. The earliest significant count is of 90 on 26 November, though numbers do not appear to increase notably until mid-December.
BEHAVIOUR, FORAGING & DIET
The flock of birds present in Deep Bay in the winter and early spring period often begins to form as the high tide recedes from the mangrove in front of the boardwalk hide, though it is erratic in its presence. Small groups of birds, presumed to be on passage, are also seen in inshore waters such as those north of Lantau.
RANGE & SYSTEMATICS
Breeds from Iceland and northwest Europe through Scandinavia east to north Siberia as far as the Taimyr Peninsula, apart from barabensis which breeds in Central Asia. It carries out short to long-distance migrations to wintering areas that extend from western Europe down to equatorial Africa, east Africa, the Middle East to India and across to south China and east Asia; also, a regular non-breeding visitor to north America (Burger et al. 2020). In China it occurs in all coastal areas (Dierschke and Heintzenberg 1994, Liu and Chen 2020, Birding Beijing 2022).
Taxonomic treatment varies according to authority. IOC places birds breeding in northern Siberia and wintering in east Asia within L. fuscus following Collinson et al. (2008). Five subspecies are recognised by IOC, among which L. f. heuglini breeds north of the Arctic Circle from north Russia to north central Siberia; birds from the east of this area are presumed to winter in east Asia, including south China. Three subspecies breed to the west (graellsii, intermedius and fuscus), while L. f. barabensis breeds in Central Asia and could potentially occur in HK.
Birds occurring in HK have previously been identified as Larus heuglini (fuscus) taimyrensis (Kennerley et al. 1995). However, there is considerable doubt as to the validity of this form (Collinson et al. 2008), and while birds from the Taimyr Peninsula appear to closely resemble the birds occurring in HK (Van Dijk et al. 2011), there is no objective evidence.
CONSERVATION STATUS
IUCN: Least Concern. Population trend increasing.
Figure 1.
Birding Beijing (2022). https://birdingbeijing.com/the-status-of-the-birds-of-beijing/ (Accessed 4 February 2022).
Burger, J., M. Gochfeld, G. M. Kirwan, D. A. Christie, and E. de Juana (2020). Lesser Black-backed Gull (Larus fuscus), 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.lbbgul.01
Collinson, J. M., D. T. Parkin, A. G. Knox, G. Sangster and L. Svensson (2008). Species boundaries in the Herring and Lesser Black-backed Gull complex. British Birds 101: 340-363.
Dierschke, J. and F. Heintzenberg (1994). Happy Island and Beidaihe Bird Report. Unpublished.
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.
Mullarney, K., L. Svensson, D. Zetterstrom and P. J. Grant (1999). Collins Bird Guide. Harper Collins, London.
Sung, Y. H., C. C. Pang, T. C. H. Li, P. P. Y. Wong and Y. T. Yu (2021). Ecological Correlates of 20-Year Population Trends of Wintering Waterbirds in Deep Bay, South China. Frontiers in Ecology and Evolution. Published 20 April 2021 doi: 10.3389/fevo.2021.658084
Van Dijk, K., S. Kharitonov, H. Vonk and B. Ebbinge (2011). Taimy Gulls: evidence for Pacific winter range, with notes on morphology and breeding. Dutch Birding 33: 9-21.
