IDENTIFICATION

VOCALISATIONS

The most characteristic call is an initially downslurred, penetrating, whistle, largely given at or before dawn or at dusk. In flight this may be repeated at a fast pace.

The song uttered at dawn is a pleasant medley of notes that vary considerably in pitch.

In the daytime can sometimes be heard a song variant that includes deep and harsh, rather hollow grating notes. The function of this vocalisation is unknown.

DISTRIBUTION AND HABITAT PREFERENCE

Blue Whistling Thrush is found in woodland and closed-canopy shrubland, often, but not invariably, close to streams, at all elevations. Carey et al. (2001) suggested that its stronghold was HK Island, but the 2016-19 atlas surveys showed that it is equally widespread and occurs at a similar density in much of the New Territories and on most of the islands. It is, however, largely absent from the northwest New Territories, where there is limited suitable habitat, and rather patchily distributed in the northeast. Blue Whistling Thrush also regularly occurs in urban areas, especially on HK Island, where the shaded wooded streams that it favours are often found near developed areas; but also in Kowloon where such sites as Kowloon and Kwai Chung Parks and Ho Man Tin service reservoirs provide islands of suitable habitat.

There appears to be no evidence for any major changes in the status of Blue Whistling Thrush in HK: Swinhoe (1861), Kershaw (1904), Vaughan and Jones (1913) and Herklots (1967) all considered this species to be common in suitable habitat. The four atlas surveys also suggest that its population and distribution have changed little in recent years: it was recorded in 18.9% and 18.5% of survey squares in the 1993-96 and 2016-19 breeding atlases respectively, and 20.4% and 22.0% of squares in the 2001-05 and the 2016-19 winter atlases, possibly indicating that it is now slightly more widespread than it was 20 years ago, though the broad pattern of distribution remains unchanged.

OCCURRENCE

Blue Whistling Thrush is sedentary with no evidence of any regular movements. A suggestion by Chalmers (1986) that it is more widespread and more often at lower elevations in winter than in summer was considered to be a result of observer bias by Carey et al. (2001) but does receive some support from the atlas survey data discussed above. Indeed, occasional reports from well-watched sites such as Mai Po where it is not recorded regularly, and its presence in some city parks, suggest that short distance movements do occur. The HK range is continuous and contiguous with that in Shenzhen and doubtless some cross-boundary dispersal takes place.

BREEDING

Vaughan and Jones (1913) described some aspects of breeding ecology. Nesting commences in mid-March and fledged young have been observed from mid-April. It is typically double-brooded with a second brood fledging in late June or early July, but may also be triple-brooded (Herklots 1967). A large, well-constructed cup nest is made from moss and rootlets and lined with ferns or leaves. Clutch size is usually four, though occasionally only two or three, eggs which are bluish-green overlaid to a variable extent by brown markings.

Natural nest locations include trees or, more often, rock ledges, but Blue Whistling Thrush readily takes advantage of man-made nest sites: ledges under bridges and the external elements of air conditioners appear to be particularly favoured, but ledges on the walls of occupied buildings, nest boxes and the interiors of abandoned buildings are also used (an example of the latter was an abandoned pump house at the top of Tai Mo Shan). In such locations nests are often reused for a second brood, and the same nest site may be used for a number of years.

BEHAVIOUR, FORAGING & DIET

On forested streams Blue Whistling Thrush is solitary and furtive, usually seen hopping over rocks or flying low over a streamcourse.  However, when vocalising it may choose a rather prominent perch such as a large rock or low branch and in such conditions, it is not particularly shy. It is even less shy in urban areas where it can be seen foraging on lawns in the early morning, and individuals may take advantage of night-time lighting to forage for insects attracted to lights even when it remains fully dark, readily entering open car ports or similar structures for this purpose. Barretto and Barretto (2020) observed it consuming the fruit of both Pavetta hongkongensis and Sterculia lanceolata.

Vaughan and Jones (1913) considered Blue Whistling Thrush to be insectivorous and noted that it will smash large cicadas on a stone; such use of a stone as an anvil to smash a snail shell has recently been noted in HK. Leven (2000) classed it as an insectivore-frugivore, with 93% of faecal samples examined containing invertebrate and 50% fruit remains. Invertebrates eaten were largely Isoptera and, especially, Coleoptera; however, Leven’s methodology was such that snails would probably not have been found in samples unless shells were consumed. Invertebrate prey is largely caught on the ground or in the leaf litter.

Song may be delivered at any time of year but is much more frequent in spring, when it can be heard during the day, and, to a lesser extent, autumn, when it may only be heard at daybreak.

RANGE & SYSTEMATICS

Widespread in Asia, from Afghanistan and Kazakhstan in the west, through Nepal and northeast India and throughout southeast Asia as far as Java (Collar 2020). Found in most of south and central China north to Beijing, but absent from the Tibetan Plateau, much of the northwest and the northeast (Liu and Chen 2021).

There are six subspecies: the nominate M. c. caeruleus is found in most of its Chinese range, including HK; two other subspecies are found in southwest China. M. c. caeruleus is readily distinguished from the other five taxa by its having a black bill, as the others are yellow-billed.

CONSERVATION STATUS

IUCN: Least Concern. Population trend unknown.