Vega Gull Larus vegae 織女銀鷗
Category I. Winter visitor and passage migrant; birds presumed to be L. v. mongolicus are uncommon, while those presumed to be L. v. vegae are scarce.
IDENTIFICATION
Mar. 2021, Michelle and Peter Wong. Adult L. v. mongolicus.
55-67 cm. Large gull, males larger than females. Two subspecies are considered to occur: mongolicus and vegae. With the caveat that field separation of mongolicus and vegae cannot be confirmed objectively (Collinson et al. 2008), the following describes the features used in HK in winter to identify the two taxa. Structurally mongolicus (illustrated) is generally larger, deeper in the chest, longer-billed and longer-winged.
From November most adult mongolicus have limited to barely any head streaking; if present, this is confined to the nape and sides of the neck. Compared to vegae the upperparts are paler grey, the primaries have a larger area of black and the legs are generally pinkish or peachy. Moult in adults appears to be an important distinction as most vegae complete primary replacement in December or January, while in mongolicus this occurs considerably earlier (usually no later than November). This means that primary wear is more advanced in mongolicus in the second half of winter.
Mar. 2010, Michelle and Peter Wong. L. v. mongolicus.
First-year mongolicus seen in HK are greyish overall with dark brown primaries and tail tip and a black to black-tipped bill. Fading of the plumage occurs as winter progresses and birds may become very pale by mid to late winter. The have a rather white head and underparts with only pale brown mottling on the latter, pale grey or greyish-white mantle and scapular feathers usually with contrastingly dark streaks on the nape and clear-cut dark centres to some of the mantle and scapular feathers. The tertials and scapulars appear particularly prone to wear. The tail band is usually relatively narrow, and the inner primaries are obviously pale.
Jan. 2010, Choshi, Japan. Geoff Carey. L. v. vegae.
Adult vegae may be distinguished by more of a brownish tone to the rather dense (and sometimes blotchy and extensive) head streaking, upperparts darker than adult mongolicus and slightly paler than many Lesser Black-backed Gull, pink legs, a greenish tone to the yellow bill and, by the third week of January, completed primary moult (rarely complete on Lesser Black-backed Gull in this month).
Jan. 2010, Choshi, Japan. Geoff Carey. L. v. vegae.
First-winter vegae generally darker overall with dull buff pale areas on mantle and scapulars, though fading and bleaching may occur as winter progresses. The extensive pale in the greater coverts and inner primaries and the relatively narrow browner tail band is different from Lesser Black-backed Gull.
Mar. 2015, Martin Hale. 3rd winter L. v. mongolicus.
Presumed third-winter mongolicus have extensive grey in the mantle, scapulars and some wing coverts, a black-tipped yellowish bill, relatively clean white head and underparts and broadly-fringed white tertials with irregular brown marks.
VOCALISATIONS
Calls are similar to those of other large gulls and do not appear to be useful for identification in HK.
DISTRIBUTION & HABITAT PREFERENCE
Most records of both taxa are from the late winter and early spring gull roost that forms on the falling tide in Inner Deep Bay near the Mai Po Boardwalk hides. Also seen in other intertidal parts of Deep Bay, including along the Kam Tin River, and on migration in southern waters.
OCCURRENCE
Figure 1 indicates that Vega Gull (mostly L. v. mongolicus) is a winter visitor and early spring passage migrant mainly from the second week of January to the end of March, with numbers peaking in the first half of March. Due to the paucity of high diurnal tides in November and December, it is possible that the numbers early winter are understated, as the gulls are more difficult to observe. Very small numbers occur less than annually at other times of year.
The highest count of mongolicus is 25 on 13 March 2000, comprising 13 first-years, two second-years and ten adults: such an age-class distribution appears to be broadly typical.
BEHAVIOUR, FORAGING & DIET
No information.
RANGE & SYSTEMATICS
L. v. vegae breeds north of the Arctic Circle in northeast Siberia east of the Taimyr Peninsula and winters coastally in east Asia, mainly in Japan and the Korean Peninsula. L. v. mongolicus breeds from the area around Lake Baikal southwest to northwest Mongolia and northwest China, and winters coastally from Vietnam to southern Japan (Weseloh et al. 2020) and along inland waterways and large lakes in China, sometimes in very large aggregations.
Taxonomic treatment varies according to authority. IOC, following Collinson et al. (2008,) includes the southern form breeding in the Lake Baikal to northwest China area within Larus vegae. Consequently, it recognises two subspecies: L. v. vegae breeding north of the Arctic Circle and L. v. mongolicus. However, Collinson et al. (2008) also note that it is impossible to say whether mongolicus is derived from vegae or from Slaty-backed Gull. They also note that although there are population level differences in adult plumage between vegae and mongolicus, field observations of these cannot be confirmed objectively.
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing. Both taxa placed within Arctic Herring Gull L. smithsonianus.
Figure 1.
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.
Weseloh, D. V., C. E. Hebert, M. L. Mallory, A. F. Poole, J. C. Ellis, P. Pyle, and M. A. Patten (2020). Herring Gull (Larus argentatus), 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.hergul.01
