IDENTIFICATION

VOCALISATIONS

Sings all year but is perhaps most vocal from March to May. The instantly recognisable territorial song is a lilting cadence that has an almost ethereal character.

Occasionally heard is a more prosaic, low-intensity variation that is less distinctive; this may be interspersed with calls, or the latter are incorporated into the song strophe.

The most-frequently heard call is a distinctive short rattle, like that of Manchurian Bush Warbler but notably higher-pitched and also longer due to the extra element in each note.

DISTRIBUTION & HABITAT PREFERENCE

Unknown in HK at the time of the 1993-96 breeding atlas survey, Mountain Tailorbird was recorded from just 0.5% of squares at the time of the first (2001-05) winter survey; however, in the 2016-19 surveys it was found in 5.6% of squares in the breeding season and 10.1% of squares in winter. Breeding season distribution is centred around the Tai Mo Shan massif (including the summit of Tai Mo Shan itself) and, to a lesser extent Ma On Shan, but it also occurs in the northeast and eastern New Territories, HK Island and on Lantau.

In the breeding season it is largely confined to native forest with a dense understorey, but is also found in closed canopy shrubland, the latter perhaps especially at higher altitudes. The highest numbers appear to be found in older established forest blocks, but it is not clear if there may be an element of observer-bias with such areas being better covered by birdwatchers.

It is, however, markedly more widespread outside the breeding season with wintering and perhaps dispersing locally bred birds found widely throughout HK. It is more frequently found in shrubland at this time of year and is less restricted to closed canopy shrubland. Presumed migrants also occur widely in other habitats, including city parks (there are several reports from the heart of Kowloon and the north side of HK Island). It has also been seen in gardens in city and suburban residential estates and in wetlands, where it has occurred in reedbeds and mangroves. The sea appears to be no barrier to dispersal and as well as there being many records from HK and Lantau Islands, there are reports from many of the smaller islands, including Tung Ping Chau and Po Toi (where it is a regular passage migrant and winter visitor).

OCCURRENCE

Mountain Tailorbird was first observed in HK during 8-9 October 1999 when one was found at Tai Po Kau (Lewthwaite 2007). One was seen, again at Tai Po Kau on 19 November 2001 and it was next reported, this time from Ng Tung Chai, on 21 May 2003. A small influx commenced on 23 October 2003, and over the following winter there were reports from seven sites in the central New Territories, together with the first report from elsewhere, at Ma On Shan on 14 March. Another influx of a similar size was noted from 30 August 2004 when three were seen at Ng Tung Chai, albeit with the benefit of hindsight it seems likely that these were breeding, or at least summering birds. The first proof of breeding came in 2005 at Ng Tung Chai.

Subsequently, numbers of Mountain Tailorbirds steadily increased, both as a breeding bird and as a passage migrant and winter visitor; its breeding distribution continues to expand. Whilst several forest and shrubland bird species colonised HK in the latter half of the twentieth century, the rate of increase and spread of Mountain Tailorbird was probably the most rapid, as well as being unexpected. Lewthwaite (2007) documented its rapid spread in southern China and, whilst it may be montane in the south of its range, it occurs at all elevations in Guangdong Province.

In most parts of HK it is hard to separate the pattern of occurrence and numbers of dispersing local breeding birds from movements of migrants from the north, though clearly both true migration and dispersal now occur on an annual basis. However, regular monitoring at Po Toi during 2006-2012 showed that, there at least, it is a scarce spring passage migrant from mid-February to late March and common autumn passage migrant from mid-September, with peak numbers occurring from mid-October to early December and small numbers wintering until late January.

BREEDING

Breeding was first proven on 18 May 2005 when a pair was observed carrying food at Ng Tung Chai and juveniles were observed there on 17 and 27 July of the same year. Only a single nest has been described in HK; a pair was observed carrying food to what was described as an ‘untidy ball amongst fronds’ two metres up a tree at Tai Po Kau on 29 April 2007. In addition, birds have been observed nest-building on 2 May and 11 May and carrying food on 12 May. Fledged juveniles have been seen from 4 June to 2 September. 

BEHAVIOUR, FORAGING & DIET

Mountain Tailorbird is often rather secretive, foraging singly or in pairs in shrub or shrub understorey or mid-canopy, where it forages in tangles or gleans from leaves in the manner of a Phylloscopus warbler. It regularly joins mixed flocks of warblers and small babblers in winter, though usually only one or two individuals join a flock. It is usually first detected when its distinctive song is heard.

Mountain Tailorbird is no doubt an insectivore, but observations of what invertebrates are consumed are lacking in HK.

RANGE & SYSTEMATICS

Predominantly a southeast Asian species, its range extends west to northeast India and, patchily, south throughout Indonesia (Madge 2020). In China the range of Mountain Tailorbird has expanded significantly in recent years: Cheng (1987) listed it only from Yunnan and Guangxi, but Lewthwaite (2007) showed that it was then found in much of Guangdong, and it now occurs east to Fujian as well as on Hainan (Liu and Chen 2021).

There are 16 races; most of these are confined to islands in the Philippines and the Indonesian archipelago whilst P. cucullatus coronatus is found throughout its range north of the Thai-Malay peninsula, including China and HK.

CONSERVATION STATUS

IUCN: Least Concern. Population trend stable.