IDENTIFICATION

VOCALISATIONS

Song is a rather repetitive, simple phrase that is lower in pitch and more measured than that of Red-whiskered Bulbul.

In general calls and subsong are lower in pitch and throatier than those of Red-whiskered Bulbul.

Less relaxed calls have a rattling quality.

Flocks of birds may be heard mobbing potential predators.

Some calls are similar in pitch to those of Red-whiskered Bulbul.

DISTRIBUTION & HABITAT PREFERENCE

Chinese Bulbul is the most widespread bird species in HK in both summer and winter. It was recorded from 78.1% and 81.2% of squares in the 2016-19 breeding and winter atlases, respectively. Whilst it remains abundant and almost ubiquitous, and is present on even the smallest offshore islands, it seems that its range may have declined slightly since the 1993-96 breeding and 2001-05 winter atlas surveys, when it was recorded from 87.2% of squares in summer and 92.3% of squares in winter. Comparison of the atlas distribution maps suggests that there may have been a decline in the degraded hills of the Castle Peak area, but otherwise there is no very clear geographic pattern and hence it is perhaps unwise to read to much into this apparent decline.

What is clear, however, is that there has been a change in the relative abundances of Chinese and Red-whiskered Bulbul, with the latter species (the second most widespread bird in HK) now outnumbering Chinese Bulbul in much of HK in both the breeding season and in winter. This represents a change from the view expressed by previous authors, notably Herklots (1953) and Carey et al. (2001), that Chinese Bulbul was the more abundant of the two species. Whilst the first breeding season atlas was not quantitative, comparison with the 2001-05 winter atlas surveys suggests that Red-whiskered Bulbul has increased in numbers over the intervening period, perhaps especially in the northwest New Territories and around the main urban areas of HK Island and Kowloon, whilst numbers of Chinese Bulbuls appear to have shown little change.

Whilst this is acknowledged to be speculative, habitat preferences and competition with other insectivore-frugivore species may provide a clue as to the differences in fortunes of the two species since the time of the first atlas surveys. Whilst both species are generalist insectivore-frugivores that occur in most terrestrial habitats in HK, Chinese Bulbul is the more abundant in shrubland, plantation and forest (Kwok and Corlett 1999, Leven 2000, Chan 2004), whereas Red-whiskered Bulbul shows a preference for edge and more modified habitats such as city parks and other urban locations (Chan 2004). There are few common insectivore-frugivores other than the much smaller Swinhoe’s White-eye in these more anthropogenic habitats, whereas in forest, especially older and more mature stands, there are several similar-sized forest specialists including two other bulbul species with which it is reasonable to assume that Chinese Bulbul must compete. Meanwhile, in edge habitats there are few competitors to constrain an increase in numbers of Red-whiskered Bulbuls.

Unlike Red-whiskered Bulbul, as is noted by Carey et al. (2001), Chinese Bulbul has been regarded as common to abundant by all previous authors back to 1860 (Swinhoe 1861) and there is no evidence of any change in status other than that discussed above. 

OCCURRENCE

As far back as the time of Vaughan and Jones (1913) it has been known that the breeding population of Chinese Bulbul is augmented by arrivals from further north between October and April. However, as was noted by Carey et al. (2001), it is still not clear how much of the population is truly migratory, rather than dispersive or nomadic, and it is still not known whether birds seen arriving in spring or departing to the south in late autumn are all passage migrants or whether a portion of the HK breeding population is migratory. Similarly, it remains the case that despite thousands of Chinese Bulbuls having been ringed in HK, there have been no recoveries elsewhere.

In spring, flocks believed to be migrants have been reported in recent years between 14 March and 13 April (with one outlier of six flying northeast over Po Toi on 18 May 2007) from several migrant watch sites, especially Po Toi (where migrants are easy to distinguish from birds making local movements), but also Mai Po and, notably, several sites in the eastern New Territories. Such spring flocks typically comprise of 50 to 500 birds; the largest aggregations noted is three flocks totalling 2,500 birds in flight over the Tolo Channel on 5 April 1997 (Carey et al. 2001), over 1,000 birds more than 3km out at sea over southern waters on 9 April 2004 and, the highest count on record, 4,000 to 5,000, again over the Tolo Channel, at Port Island (Chek Chau) on 2 April 2010.

In autumn, migrant flocks of a similar size to those noted in spring have occurred between 21 October and 17 December; again the picture is perhaps clearest on Po Toi where most birds typically pass through between late October and late November. The highest count of a flock at this season definitely comprised of migrants was of 700 on Po Toi on 11 November 2009, though a flock of 800 at Tai O on 16 November 2013 probably also consisted of migrants.

Flocks are occasionally reported from Po Toi in midwinter, including 100 on 24 January 2006, a flock of 50 heading south there on 10 January 2007 and 60 on 12 January 2010, though whether these include birds making long distance movements at this season is unclear, as local breeding birds also make movements in winter, with some birds vacating higher altitude areas and moving downslope. Such movements are likely to be in response to food availability, with both fruit and invertebrates being at their annual lowest point in hillside forest and shrubland in the late January to late March period (Corlett 1998, Leven 2000).

Like Red-whiskered Bulbul, Chinese Bulbul forms communal roosts, especially in autumn, but these are less well documented than those of the former species. Counts in recent years include at least 50 at Ping Shan Chai prior to entering a roost in long grass on 29 December 2001, 100 gathered in large trees at Tai Po Waterfront Park on 26 September 2002 and 560 leaving a roost at Sha Po on 29 November 2010.

BREEDING

For such a common and widespread species, surprisingly little has been published on the breeding ecology of Chinese Bulbul in HK. Vaughan and Jones (1913) stated that  it is at least double-brooded, with a breeding season extending from the end of March to the end of August; the earliest observation in recent years of fledged juveniles is on 21 April 2009. Herklots (1953) described the nest as a ‘fairly deep compact cup-shaped structure constructed of coarse grass and fibres and lined with fine roots and grass’ and that three, four, or occasionally, five eggs are laid. Herklots (1953) described these as being ‘mauve generously spotted and blotched with purple-grey’, whilst Vaughan and Jones (1913) considered that the eggs  are indistinguishable from those of Red-whiskered Bulbul.

Chinese Bulbul seems to be less inclined to construct nests close to houses, in gardens or on balconies than is Red-whiskered Bulbul, which may go some way to explaining the paucity of recent documented observations of nesting details. 

BEHAVIOUR, FORAGING & DIET

Chinese Bulbul is typically encountered as single birds, pairs or small parties foraging in groups in shrubland, forest, farmland and around fish ponds and village areas and is often one of the most conspicuous species in city parks. However, even before the recent increase in numbers of Red-whiskered Bulbuls, it was usually outnumbered by this species more anthropogenic habitats. It often occurs in mixed flocks with other bulbuls or indeed other forest species. Migrant flocks are usually found in or over forest or shrubland and tend to be dense and fast-moving.

Chinese Bulbul is an insectivore-frugivore. As is Red-whiskered Bulbul, it is largely frugivorous, especially during the November to January fruiting peak (Corlett 1998). It is markedly more frugivorous than common non-breeding migrant insectivore-frugivores which winter in or migrate through HK and somewhat less insectivorous than most common resident laughingthrushes and babblers, though both Corlett (1998) and Leven (2000) found that it takes more invertebrates than Red-whiskered Bulbul (Corlett recorded fruit in 96% and invertebrates in 39% of faecal samples, whilst Leven found 94% and 28% respectively). Fruit consumption appears to be non-selective, subject to the fruit being sufficiently small (up to c. 10mm) to swallow or sufficiently soft to be pecked apart (Leven 2000). Invertebrates consumed were found by Leven (2000) to be largely Areinida, Formicidae and, especially, Coleoptera.

Most food, whether fruit or invertebrates, is foraged in the tree or shrub canopy though fallen fruit is also eaten and, like Red-whiskered Bulbul, Chinese Bulbul will readily hawk for alate termites; sally-hunting for flying insects is common, especially on still spring evenings when insect emergences occur. Chinese Bulbul will also utilise temporary abundances of invertebrates, for example foraging in emergent wetland vegetation to take advantage of the presence of large numbers of teneral damselflies, and will readily consume food scraps such as bread, rice or noodles accidently or deliberately provided by people. Unlike Red-whiskered Bulbul, however, it does not appear to readily consume leaves in the cold winter weather.

As HK’s most widespread and one of its most abundant, frugivores, Chinese Bulbul, together with Red-whiskered Bulbul, are the most important dispersal agents for many forest and shrubland trees and shrubs, and hence are of major importance in aiding the recovery of HK’s forest cover (Corlett 2011). Weir and Corlett (2006) used radio-telemetry to track Chinese Bulbuls and  estimated potential dispersal distances from gut passage times for seeds. They found that Chinese Bulbul could potentially disperse seeds up to 1,300m (which would be far enough to connect many isolated patches of woodland in ravines on degraded upland hillsides, for example), though median disperments were much lower at approximately 100m.  

RANGE & SYSTEMATICS

Until the late twentieth century Chinese Bulbul was resident in, and restricted to, northern Vietnam and central and eastern China, west to eastern Yunnan and eastern Sichuan and north to Xian and Shanghai (Cheng 1987). However, in recent years it has spread west to western Yunnan and southern Tibet and north to central Gansu and Ningxia in the west and Liaoning and Korea in the east. Many birds breeding in the north of its range are summer visitors, but Chinese Bulbul is now common throughout the year at least as far north as Beijing (Liu and Chen 2021, eBird 2021).

There are four races, three of which are found in China (the fourth is endemic to the Ryukyu Islands): the nominate race is found over most of its range, including HK; P. s. hainanus occurs in Hainan and Guangxi Provinces, whilst P. s. formosae is endemic to Taiwan. Occasionally birds are reported that in plumage resemble P. s. hainanus in being darker around the head, though the significance of these is unclear; most such records are in early winter which is a likely time for dispersing birds to reach HK, but it is also the time of year when annual moult has just been completed and feathers are least abraded and it may simply be the case that darker-headed birds are simply showing less feather wear.

CONSERVATION STATUS

IUCN: Least Concern. Population trend increasing.