IDENTIFICATION

VOCALISATIONS

The call is based around a harsh ‘chak’ note that is relatively low in pitch. It may be uttered singly, or more often as two to three notes in a very short duration rattle.

More excited birds run these notes together as a longer rattle.

The song heard in HK is rich and loud. It usually begin with a short series of low-pitched notes followed by a short explosive phrase.

Birds that lack or have a poorly-developed introductory phrase tend to have the rest of the song also less structured.

DISTRIBUTION & HABITAT PREFERENCE

Occurs in shrubland and open country areas with sufficiently dense areas of shrub or shrub-grass mix, and at the margins of closed-canopy shrubland and woodland; also occurs in reed marsh on migration. It is rarely found over 400m asl. In spring it is more likely to be recorded in the Deep Bay area, though this may in part be a function of observer activity.

Its distribution is concentrated in the northeast from Deep Bay through Lam Tsuen Country Park to Sai Kung and in the western half of Lantau. However, there was a substantial decline between the 2001-05 and 2016-19 winter atlas surveys, with 14.5% of 1km squares occupied in the earlier survey and only 5.2% in the latter. The decline was widespread, but more evident in offshore islands and western Lantau, the latter perhaps due to the spread of closed-canopy forest or shrubland.

OCCURRENCE 

Manchurian Bush Warbler is a passage migrant and winter visitor, with numbers highest in late autumn from the third week of November to the end of the year (Figure 1). A sharp fall in the first half of January may be anomalous or may reflect a response to cold weather in the form of departure and/or a decrease in the frequency of its distinctive vocalisations. Trapping records in the 1990s, which are independent of detectability by vocalisations, indicated a gradual decline in numbers up to the end of February, when an increase marked the beginning of spring passage. The pattern of field records from 1999-2020, however, indicates a slow decline from the last week of January to the first week of April, followed by a sharper decline around the middle of April. This is despite an increase in the frequency of vocalisations, both call and song, as spring approaches.

As indicated by Welch et al. (2016), there has been a decline in spring since the 1990s, when the numbers recorded on spring passage did not fall far short of those recorded in autumn; in contrast, the difference now is noticeable. Welch et al. (2016) also stated winter counts were higher in the 1990s, particularly at Mai Po.

Extreme dates are 24 October 2012 on Po Toi and 8 May 1996 at Cape D’Aguilar. The highest count is 40 at Mai Po on 15 November 1992; the highest count since 1999 is 20 at Fung Lok Wai on 29 February 2020.

One collected at Mong Tseng on 3 February 1937 (Herklots 1937) was the first HK record. It was subsequently recorded in winter by Herklots (1953), Dove and Goodhart (1955) and Walker (1958).

BEHAVIOUR, FORAGING & DIET

Generally, rather shy and difficult to see in dense shrub or rank vegetation. Easier to observe early morning when it comes to edge areas, but in warmer part of day moves deeper into shrubland or even woodland.

Birds can be heard in song from late January to the end of spring passage, though mainly from the end of February.

RANGE & SYSTEMATICS 

Two subspecies are recognised. The nominate breeds in central and east China as far as the coast and north at least as far as Beijing, while borealis breeds in the coastal provinces of northeast China, adjacent Ussuriland and much of the Korean peninsula. In the non-breeding season occurs in south and southeast China coastal provinces, including Taiwan and Hainan, and north Vietnam. The northerly taxon borealis is considered to winter in Taiwan and to reach the northern Philippines (Liu and Chen, 2020, del Hoyo et al. 2020, Birding Beijing 2022).

CONSERVATION STATUS

IUCN: Least Concern. Population trend stable.