IDENTIFICATION

VOCALISATIONS

A vocal species, many of whose utterances have a distinctive optimistic timbre. The song may be a repeated simple phrase, or this may be interspersed with a variety of high-pitched churrs and other notes. Somewhat mimetic, occasionally uttering sounds of other species such as Oriental Magpie-Robin or Yellow-cheeked Tit.

Prior to going to roost, a variety of chattering and other calls may be uttered by groups of birds.

When agitated, repeatedly utters churring and other notes.

Occasionally, unusual calls such as the following are heard.

DISTRIBUTION AND HABITAT PREFERENCE

Chestnut Bulbul is now a characteristic species of mature secondary forest in HK. It was found in 12.6% of squares in the 2016-19 breeding atlas survey, largely in the central, northeast and east New Territories, with small numbers recorded on Lantau and HK Island. This represented a marked increase from only 3.7% of squares in the first breeding atlas survey of 1993-96, at which time it was largely confined to the central and northeast New Territories. In winter, when numbers are bolstered by migrants arriving from the north, it is more widespread, having been found in 25.1% of squares in the 2001-05 and 22.0% of squares in the 2016-19 surveys respectively. In winter, as well as occurring more widely on HK Island and on Lantau, it is not confined to more mature woodland, being found in shrubland and smaller wooded areas and even patches of trees in gardens and other edge habitats.

OCCURRENCE

Chestnut Bulbul colonised HK in the late twentieth century, being one of the first wave of species to colonise, or more likely recolonise, in response to increased habitat availability as trees were planted and forests regrew. As was noted by Carey et al. (2001), it was first recorded in HK at Kowloon Reservoir on 14 March 1936, with further records in both early and late 1941. However, it was not recorded again until 1954 (Herklots 1967), and it remained an irruptive winter visitor in the late 1950s, the 1960s and the 1970s, with none recorded in some winters including the period from 12 February 1978 to 19 December 1981. The first evidence of breeding came from Tai Po Kau in 1982 where birds remained over the summer and a party of five, including one carrying food, were seen on 26 June (Carey et al. 2001). There were only three records in 1983 and none were recorded in 1984 and 1985; however, perhaps not too much weight should be afforded to this apparent absence as during the period from 1984 to 1989 a full systematic list was not published in the HKBR, resulting in a significant decline in the number of records submitted by observers.

Regardless of this, Chestnut Bulbul was recorded again at Tai Po Kau in summer in 1986, since when it has been present there throughout the year, It subsequently spread across woodland in the central and eastern New Territories: Carey et al. (2001) noted that, in addition to Tai Po Kau, it was then established at Tai Lam CP, Kap Lung, Ng Tung Chai, Shing Mun, Lead Mine Pass, Kowloon Hills, Ma On Shan, Ho Chung and Wu Kau Tang. Since that time the breeding range has continued to expand, most notably in the Sai Kung peninsula, which is now a stronghold, and it is now well established in much of the northeast. Chestnut Bulbuls are now also found on both HK Island and on Lantau during the breeding season; numbers are currently small but widespread observations on Lantau suggest that numbers and range are likely to increase there too.

As discussed above, Chestnut Bulbul first occurred in HK as an irruptive and irregular winter visitor, with records falling between 18 November and 7 April with none seen in some winters (Herklots 1967). Despite its establishment as a breeding species, Carey et al. (2001) suggested that it was probably less widespread in winter than previously, noting that there were no records from HK Island between April 1983 and February 1995. Since that time, irruptions appear to have become more frequent again, with significant influxes noted in 1998/99, 2003/04, 2005/06, 2008/09, 2009/10, 2010/11, 2013/14, 2015/16, 2016/17 and 2019/20; however, as the breeding population has increased and spread it has become increasingly difficult to distinguish between winter migrants and dispersing breeding birds.

Migrants from the north typically arrive in early to mid November, at which time flocks are now often seen at migration watchpoints such as Mai Po, Tsim Bei Tsui (where observations include flocks of 100 and 65 seen arriving from over Deep Bay) and Po Toi. Earlier records such as one on Po Toi on 29 July and 30 September 2008 and two at Mai Po on 10 June 2018 seem most likely to be dispersing local breeding birds. Migration seems to be largely over by early December, though records from Po Toi include evidence of new arrivals as late as 29 December.

Return movements northwards are less obvious than autumn arrivals at most sites, though they include occasional urban records such as a bird at Homantin on 15 February 2016. However, several recent years have seen April concentrations at Tai Po Kau Headland, including 264 there on 11 April 2009, 466 (the record high count for HK) on 7 April 2011 and 250 on 16 April 2017 – all three of these counts came at the end of winters where there had been significant irruptions.

BREEDING

The breeding ecology of Chestnut Bulbul in HK does not appear to have been studied; the few incidental observations include nest building observed on 21 March, 5 April and 1 May, adults carrying food on 7 May and 26 June, an adult feeding pulli on the rather late date of 19 September and recently fledged young on 20 May and 9 August. In view of the large spread of dates of breeding activity it seems likely that, like HK’s better studied bulbuls, Chestnut Bulbul is double or perhaps sometimes triple-brooded.

BEHAVIOUR, FORAGING & DIET

Chestnut Bulbul is typically encountered in small noisy flocks of about five to ten, occasionally up to 20, birds moving through the canopy where they tend to keep high and in cover and hence can be quite hard to see. Migrants occur as single birds, small parties and as larger flocks of up to 50 individuals; flocks can be conspicuous, especially when they occur in more open country; migrant flocks may call loudly from a group of trees before departing en masse, often flying for considerable distances.

Diet has not been studied in detail in HK, but observations suggest that Chestnut Bulbul is, like HK’s other bulbuls, primarily frugivorous with some insects being eaten. Fruit that has been seen consumed includes that of native trees Photinia benthamiana, Machilus sp. and Ilex rotunda, shrubs Schleffera heptaphylla, Psychotria asiatica and Callicarpa sp. and the woody climber Psychotria serpens. Invertebrates are probably largely obtained by gleaning, though an interesting observation is that of one hovering in front of a spider’s web and successfully plucking the spider from it.

RANGE & SYSTEMATICS

Occurs in northern Vietnam and south and east China north to Hubei, Hubei, Hunan and Jiangxi (Fishpool and Tobias 2020). There are two races: the nominate race occurs in Hainan and northern Vietnam, whilst H.c. canipennis is found through the remainder of its range including HK (Liu and Chen 2021).

CONSERVATION STATUS

IUCN: Least Concern. Population trend increasing.