IDENTIFICATION

VOCALISATIONS

A down-slurred and drawn-out ‘kreeeyah’ is frequently uttered.

Also, a ‘krek’ or ‘krek-krek’ usually when foraging.

DISTRIBUTION & HABITAT PREFERENCE

In the 1970s flocks numbering several hundred birds could be found at several sites including Deep Bay, Victoria Harbour, Tolo Harbour and Starling Inlet. They appeared to show little preference for any locality although 2,000 in Victoria Harbour on 6 February 1972 was the highest count. Reduced food availability due to re-siting of sewage outfalls into deeper waters combined with improvements in sewage treatment and disposal may have caused a shift in the distribution of the wintering population from the Victoria Harbour area to Deep Bay. Numbers at the latter site increased from winter 1977/78, and most records are now from there.

Away from Deep Bay generally up to 100 have been recorded in western waters around Lantau and in Tolo Harbour, a decrease from the up to several hundred that remained regular in coastal waters throughout Hong Kong in the 1990s. By far the highest count away from Deep Bay this century is 280 between Tung Chung and Outer Deep Bay on 7 February 2015.

OCCURRENCE

Black-headed Gull is an abundant winter visitor, mainly to Deep Bay, but numbers have declined substantially since the 1990s. A significant arrival to Deep Bay occurs in November, with numbers increasing to a peak in January; by mid-February numbers are in decline and a more significant departure occurs during the ensuing month.

Surveys at sea between 1995 and 1997 to the north of Lantau and in Victoria Harbour during the period 1974 to 1980 indicated passage occurs from at least mid-February. Since 1999 the highest count in the first half of April is 1,000, while in the second half it is 523. Up to six have been noted during June, July and August, though over-summering birds are not noted every year.

Vaughan and Jones (1913) stated Black-headed Gulls occurred in ‘considerable numbers’ from the third week of October until February or March, though this assessment does not necessarily apply specifically to HK. Herklots (1967) stated up to 100 had occurred in Deep Bay and that it was less frequently seen in the harbour; until the 1970s Black-headed Gull remained a relatively scarce winter visitor to Deep Bay and Victoria Harbour. Numbers rarely exceeded 100 in the early 1960s, but toward the end of that decade an increase became apparent when flocks of 100 to 200 were a regular feature, and an estimate of 1,000 birds in the western approaches to Victoria Harbour on 27 December 1968 was the highest count.

The winter of 1974/75 saw a large increase in the numbers recorded in HK, due in part to the discovery and regular counting of a roost in the West Lamma Channel. The highest counts of this roost were 6,500 on 23 January 1975, 10,470 on 26 January 1977 and 10,788 on 13 December 1977. Coordinated counts at fortnightly intervals during the winter of 1977/78 at several locations produced an estimated total wintering population of approximately 25,000 birds (Melville 1980).

The estimated wintering population in the mid-1990s was slightly lower at approximately 20,000 (Figure 1), with a much-changed distribution centred on Deep Bay (see above). Further decreases in the size of the wintering population have occurred since. The winter periods from 1996/97 to 2007/08 generally saw 10,000 to 14,000 birds recorded in Deep Bay during the winter waterbird counts, but since then the highest count has been substantially lower at 7,000 on the HK side of Deep Bay and 9,000 in the whole bay. Based on winter waterbird counts in Deep Bay Sung et al. (2021) concluded that the wintering population of Black-headed Gull in HK declined from 1998 to 2017. Given the large population wintering to the north, it is possible that milder winters associated with climate change have meant fewer bird visiting in the non-breeding season.

BEHAVIOUR, FORAGING & DIET

Whereas in western Europe Black-headed Gulls in the non-breeding season readily take food arising from anthropogenic activities of man such as rubbish tips or direct feeding, this appears to not be the case in HK. Birds are seen taking food items from the surface of water bodies, whether the sea or commercial fish ponds, usually by dropping down from the air but also when swimming. Previously large numbers of birds foraged in Victoria Harbour probably as a result of nearby sewage outfalls. Gregarious, forming large and vocal flocks on the mudflats when the tide is rising.

RANGE & SYSTEMATICS

Monotypic. Breeds from Iceland and more northerly parts of Europe east through the Black and Caspian Sea areas, Kazakhstan, sub-Arctic Circle Russia and northeast China to Sakhalin and Kamchatka; winters coastally in the north Atlantic, Mediterranean, Middle East, western and northern Indian subcontinent, Indochina and east Asia as far north as Hokkaido (Burger et al. 2020). In China breeds across northern parts from Xinjiang to Heilongjiang, and winters in lowland areas from the Yellow River south (Liu and Chen 2020).

CONSERVATION STATUS

IUCN: Least Concern. Population trend unknown.