IDENTIFICATION

VOCALISATIONS

The song is a rich warble, lower in pitch and richer than Lesser Shortwing (which may occur in similar habitat). Calls include a short ‘chip’ contact call, a typical babbler-like chatter that resembles a less excited Huet’s Fulvetta and a distinctive three or four-note ‘pee-pee-pee.’ When agitated or alarmed a dry throaty at times buzzing chatter is given.

Vocalisations of this species are not freely available on Xeno-canto.

DISTRIBUTION AND HABITAT PREFERENCE

Over time, Red-billed Leiothrix has been seen at widespread locations in the mainland New Territories, on HK Island and in the urban area of Kowloon. Small numbers of birds have also been reported from Lantau over the years and there is at least one record from Cheung Chau (in April 2000). However, in the early to mid 1990s when both its numbers and range appear to have been greatest, the main centre of distribution was the central New Territories at Shing Mun, Tai Po Kau, Lam Tsuen valley and, especially, Tai Mo Shan.

Since that time, the distribution of Red-billed Leiothrix has shrunk and it is now largely confined to the area around the Tai Mo Shan massif, especially the higher elevations of Tai Mo Shan itself. Thus, whilst it was found in 2.4% of squares in the first breeding atlas survey of 1993-96 and 1.9% of squares in the winter atlas survey of 2001-05, in the 2016-19 surveys it was only found in 1.4% of squares in the breeding season and 1.1% of squares in winter. Some of this decline appears to relate to the near-disappearance of birds from urban parks on HK Island and in Kowloon where, as was suggested by Carey et al. (2001), the populations may always have been dependent on the release of captive birds, but it also seems to have declined in the New Territories.

The reasons for the decline in the New Territories are uncertain. Some of the decline may be attributable to a reduction in the release of ex-captive birds, but it is also possible that, as was suggested by Leven and Corlett (2004), Red-billed Leiothrix may directly complete with the closely related Silver-eared Mesia, which has increased in range and numbers during the period and appears to occupy a similar niche. Such competition is hard to demonstrate; however, it might explain why Red-billed Leiothrix appears to have declined at Tai Po Kau and Shing Mun, both former strongholds and sites where Silver-eared Mesia is now numerous.

Furthermore, if the two species do compete, it might  be predicted that Silver-eared Mesia, which is essentially a tropical species (e.g. Robson 2000), might be more likely to dominate at lower altitudes in HK. Conversely Red-billed Leiothrix breeds at higher altitudes in the Himalayas where the two species are naturally sympatric, albeit there is some overlap and the two species occur in mixed flocks (Salim Ali and Ripley 1996). It also has a much more northerly distribution in China (Liu and Chen 2021) and was (at least formerly) a hill bird in Guangdong with a lower elevational limit of 500m (Lewthwaite 1996). Thus it might be better able to compete at higher altitudes in HK, where periodic low winter temperatures appear to have a significant effect on vegetation and animal communities above about 500m elevation (e.g., Dudgeon and Corlett 1994). There is some evidence that this is indeed the case; in the 2016-19 breeding season survey the area with the largest numbers of Red-billed Leiothrix was around Tai Mo Shan, where it is quite common as high as the summit, which was not the case for Silver-eared Mesia.

Red-billed Leiothrix occurs in secondary broadleaf forest, especially where there is a well-developed understorey. It appears to particularly favour areas of dwarf bamboo, both where these occur in forest and where these occur in patches in shrubland / grassland mosaic habitat on the higher slopes of the hills. In this respect it may differ from Silver-eared Mesia, which does not appear to particularly favour dwarf bamboo. Records from more anthropogenic habitats such as city parks are presumed to be of recently ex-captive birds or their descendants.

OCCURRENCE

The status of Red-billed Leiothrix in HK has been a source of controversy from the time of the first reported occurrrences. These concern two single observations (the number of individuals is not stated) from Kowloon in April and HK Island in May documented by Vaughan and Jones (1913), who considered that the it was ‘possible, though not likely’ that these were ex-captive birds.

Subsequently, as is discussed in detail by Carey et al. (2001), opinion swung back and forth as to whether some birds occurring in HK were genuine migrants from further north or all were ex-captive individuals: Herklots (1953) considered it ‘Occasional’ with records possibly relating to ex-captive birds, while in his later work (Herklots 1967) he suggested that the seasonal and spatial pattern of occurrence at that time ‘mainly between January and May from widespread localities’ suggested that some might be of natural origin. Conversely, Webster (1975) advocated a cautious approach and considered that it could not be proven that any HK records related to naturally occurring individuals, but Chalmers (1986) placed it on Category A of the HK list on the strength of ‘consistent’ ‘scattered reports … of small flocks … in non-urban areas … between October and May’. Most recently, however, a review detailed by Carey et al. (2001) concluded that neither the spatial nor seasonal pattern of records supported the proposition that any birds occurring in HK were other than ex-captive individuals or their descendents, and Red-billed Leiothrix was placed in Category IIA as a southeast China breeding species with an established HK population of captive origin.

No evidence has emerged since then to challenge this conclusion, but it is relevant to note that, whilst Red-billed Leiothrix was considered to be a hill bird in Guangdong by Lewthwaite (1996), it is now present at a number of sites in and around Guangzhou and Shenzhen including Wutongshan (eBird 2023). These birds seem likely to be ex-captive birds or their offspring, as is the case in HK; however, these populations potentially link the HK population and the naturally occurring birds further north in Guangdong.

BREEDING

Red-billed Leiothrix is presumed to have bred in HK since the early 1980s; however, instances of proven breeding (rather than numbers present in suitable breeding habitat in the spring and summer months) are few. Thus, whilst Chalmers (1986) stated that breeding was confirmed in HK in June 1985, a observation that was repeated by Carey et al. (2001), this assertion is not supported by Chalmers (1987) who stated that ‘high numbers at Shing Mun and Tai Po Kau in [the] summer months [of 1985] indicated probable breeding’. In fact, the first documented proven breeding record did not come until 1991 when a pair were seen with a dependent juvenile at Lead Mine Pass on 12 October. Subsequently there appear to be only three proven breeding, or at least attempted breeding, records: a pair nest-building in Kowloon Park on 6 April 1993, an adult and juvenile together at Tai Mo Shan on 22 May 2005, and a juvenile seen there on 1 August 2011. Apart from these scant details , breeding ecology appears to be unstudied in HK.

BEHAVIOUR, FORAGING & DIET

Red-billed Leiothrix occurs as singly, in pairs or in small flocks, either with its own species, with Silver-eared Mesias,  or in mixed warbler or babbler flocks. Flocks are typically quite small, consisting of fewer than ten individuals, but counts of up to 20 individuals are not unusual. When in flocks it forages at all levels from deep in the understorey to the lower canopy (though the latter is usually only used where there are tangles of creepers or dead leaves). Flocks are usually easy to see but single birds or pairs can be quite furtive, especially when deep in dwarf bamboo clumps.

Red-billed Leiothrix is an insectivore-frugivore and was considered to be highly frugivorous by Corlett (1998), who found fruit remains in 96% and invertebrate remains in 58% of faecal samples examined. Leven (2000) found fruit remains in 72% and invertebrate remains in 100% of samples examined, suggesting a less frugivorous diet, possibly because Corlett’s sampling effort was concentrated in late October to mid December, a period that coincides with the period of peak fruit availability at his study sites (Leven 2000), whilst Leven was sampling throughout the winter. As with most insectivore-frugivores in HK, fruit appears to be consumed opportunistically (i.e. the most readily available fruit is consumed), whilst invertebrates consumed were found by Leven (2000) to be predominantly Coleoptera (43% of identified remains) and Araneida (25.5%), both groups that contain numerous species and individuals in the tree and shrub canopies where it largely forages.

RANGE & SYSTEMATICS

The native range of Red-billed Leiothrix extends from northwest India, eastwards through the Himalayas and throughout south and central China as far north as Sichuan, Shaanxi and Jiangsu. In addition feral populations are established in Taiwan, Japan, Hawaii and parts of southern Europe (Liu and Chen 2021, eBird 2023, Male et al. 2020).

There are five races, four of which occur in China; the race L. l. kwangtungensis of northern Vietnam, southeast Yunnan, Guangxi and Guangdong (Cheng 1987) is most likely that which occurs in HK, but this has not been confirmed.

CONSERVATION STATUS

IUCN: Least Concern. Population trend decreasing.