IDENTIFICATION

VOCALISATIONS

A loud and low-pitched clicking is most often heard; there is some variation in pitch of this call.

A buzzing and grating ‘vzzzcht’ not unlike Amur Stonechat.

Also, a loud and deep churring rattle probably uttered in alarm.

The song is most often heard from April to July but is occasionally uttered at other times of the year.

DISTRIBUTION & HABITAT PREFERENCE

Oriental Reed Warbler is largely recorded in wetland habitats such as reed marsh, mangrove, freshwater marsh, vegetated large river channels and wet agricultural areas, with Phragmites reeds and grasses being the preferred habitat. However, it is occasionally encountered at other sites such as urban parks, bamboo stands and landscaped areas on passage.

Most records are from the Deep Bay area, but it is also recorded at other widespread sites on Lantau and Chek Lap Kok, around Three Fathoms Cove, the site of the former airport at Kai Tak, offshore islands and urban locations such as Ho Man Tin and Kowloon Park.

OCCURRENCE

Oriental Reed Warbler is a passage migrant, common in autumn, uncommon in spring, and is scarce to rare in winter and summer.

The most systematic dataset available for this species comes from the constant-effort trapping programme at Mai Po from the last week of August to the last week of May during the winter periods from 2008/09 to 2020/21 (Figure 1). These data show that it is rare in the last week of August, and numbers increase to peak during the last two weeks of September and the first week of October. The subsequent decline occurs at the same rate to the last week of November, after which numbers remain very low throughout the winter. Return passage is obvious by at least the final week of March, but spring passage is relatively weak, despite continuing to the middle of May in most years, and occasionally the end of May.

When comparing ringing data up to 1997 with those collected from 2001 to 2011, a decline was noted in peak counts in spring by Allcock et al. (2013) and Welch et al. (2016), who postulated an unknown regional factor to be at play. Although differences in trapping site could not be ruled out, Allcock et al. (2013) noted that wing length of birds trapped in spring is significantly longer than those trapped in autumn, suggesting that different populations pass through in each season. Dyrcz and de Juana (2020) note that Oriental Reed Warbler is “in many regions … suffering from habitat loss through e.g., canalization of riverbeds and land reclamation”.

The first midsummer record occurred in 1981, and there are occasional records in June but even fewer in July and the first half of August.

The highest counts are all from the Deep Bay area: 300, of which 200 were present around a single pond, at Lin Barn Tsuen on 25 September 1997 and 200 at Mai Po on 27 September 2003. However, since 2004 the highest count is only 80, at Mai Po on 14 October 2015. The large concentrations on the overgrown grassy bunds of fish ponds, which were a feature of autumn in the 1990s and the early years of this century, appear to be a thing of the past.

It was described as a passage migrant by Vaughan and Jones (1913) and Dove and Goodhart (1955), the latter of whom had the first HK record on 13 September 1953.

BREEDING

Single partially built nests presumed to be of this species were discovered at Mai Po in 1987 (Melville 1988) and during the 1993-96 Breeding Bird Survey; there is no evidence of successful breeding, however.

BEHAVIOUR, FORAGING & DIET

Vocal and obvious in reed marsh and grassy habitats on passage, and frequently seen in flight when flushed or moving between foraging areas at times of peak passage. Somewhat clumsy foraging action in the taller reeds and grass that it requires.

Autumn birds may linger in the reed marsh for up to two months and re-trap rates are relatively high at over 10%. Year-on-year re-trap rates are also high, with the oldest birds trapped eight years after ringing (Allcock et al. 2013).

RANGE & SYSTEMATICS

Monotypic. Breeds in the eastern half of Mongolia east to northeast China and adjacent parts of Ussuriland and Sakhalin south through Japan and Korea to east China; winters in Indochina, southeast Asia and Sumatra (Dyrcz and de Juana 2020). In China it breeds in much of the eastern half of the country but away from south coastal areas (Liu and Chen 2020).

CONSERVATION STATUS

IUCN: Least Concern. Population trend decreasing.