IDENTIFICATION

VOCALISATIONS

The typical call heard in HK is a throaty ‘raaow’.

DISTRIBUTION & HABITAT PREFERENCE

Most records occur in Deep Bay, either in the intertidal areas or on Mai Po NR when birds are roosting. Previously there was a winter roost at Pak Nai in Outer Deep Bay, but this disappeared in the late 1980s due to human disturbance. Up to eight birds have been recorded elsewhere in southern waters mainly in spring, off Cape D’Aguilar during 1-2 May 1999 during the passage of a tropical storm and in scattered inshore water locations. The former marsh at San Tin was a preferred late spring stopover in the 1970s and early 1980s, when birds were regularly present throughout late May and early June, the highest count being up to 37 between 24 May and 17 June 1980.

OCCURRENCE

Primarily a passage migrant in the last week of March and first half of April, numbers peak in the first week of the month (Figure 1). Migrants first appear in the third week of February and are largely gone by the middle of May.

The highest count in HK is 270 on 2 April 2020, followed by 170 on 7 April 2012. Figure 2 indicates that there is some variation in peak spring counts, with particularly low numbers recorded from 1997 to 2002 and during 2005-08. The five-year mean of peak counts has returned to slightly below the levels recorded in the late 1980s and early 1990s.

Since 1987 records of Caspian Tern from June to September have been less than annual, and the highest count only seven. This contrasts with the period 1973-86 when there were records from late June to October each year, with groups of up to eight birds recorded. November sees either late passage or the arrival of wintering birds, but no double-figure counts have occurred in the rest of the year.

Prior to 1966 there were no winter records. A small wintering population became established at Pak Nai in Outer Deep Bay in the early 1970s, rapidly increasing after 1972-73 to peak at a high of 80 on 20 February 1977. In the early 1980s a gradual though irregular decline set in, and after the winter of 1986-1987 the wintering population did not exceed 14 birds. The number of wintering birds continued to fall until the winter of 1987-88, the last time Caspian Terns wintered at Pak Nai. Since 1990 no more than eight birds have been recorded in winter and all such records since 1989 have been from Inner Deep Bay.

BEHAVIOUR, FORAGING & DIET

Rarely seen foraging in HK, and so is presumed to feed mostly on fish at sea or in inshore waters. Generally seen at roost on the intertidal mudflats of Deep Bay in the winter or on Mai Po NR in the spring, often together with Gull-billed Terns.

RANGE & SYSTEMATICS

Monotypic. Distributed worldwide but populations scattered and relatively restricted. Breeding populations present in central North America, Scandinavia, southeast Europe, Central Asia and Mongolia; winters in southern North America, Africa, the Indian subcontinent and south China, with resident populations in Australia and Madagascar (Cuthbert and Wires 2020). In China locally common in Xinjiang, the northeast and coastal areas during the summer, and winters coastally in southeast China, including Hainan and Taiwan (Liu and Chen 2020).

CONSERVATION STATUS

IUCN: Least Concern. Population trend increasing.