IDENTIFICATION

VOCALISATIONS

A very vocal species. The characteristic song from which derives its name is a loud two-note phrase ‘ko-el’ uttered in a series that accelerates and rises in pitch sometimes to a shrill scream.

When chasing another male, the following call, which may also be heard in a less frantic form at night, is given.

Also uttered is a loud ‘kik-kik-kik-kik-kik’.

The female gives a bubbling series of ‘ki-ki-ki’ notes.

DISTRIBUTION & HABITAT PREFERENCE

In the breeding season, Asian Koels are distributed widely across the lowlands of the northern New Territories and locally in other parts of the New Territories, in Kowloon and on HK Island and Lantau; in some years they are also reported from Lamma and smaller islands such as Cheung Chau and Po Toi. Outside the breeding season, they are much less widespread and are found locally in the New Territories, especially at Mai Po in autumn, and occasionally Kowloon, HK Island and Lantau but are absent or evade attention elsewhere. At all seasons they show a strong preference for fung shui woods and stands of trees on the fringes of farmland, fishponds and marshes. They can also be found in orchards, urban parkland and gardens, but generally avoid forest and unbroken areas of shrubland.

OCCURRENCE

Reported in all months of the year. From a relatively low base in January-February (8.5% of total records), numbers rise in March-June (35%) and again in July-October (50% including 17% in September, the peak month), before rapidly returning to low levels again in November-December (6%) (Figure 1). Whereas a high proportion of records in March-June, when the breeding season is at its height and adults are most vocal, is of birds detected through their vocalisations, nearly all of the larger counts in September and October, when vocal activity is greatly reduced and the population is augmented by migrants and local post-breeding dispersal, are of birds detected visually.

Counts of 20 birds or more are reported at Mai Po in most years, typically between the middle of August and the middle of October, the two highest being 37 on 2 October 2011 (including 28 individuals in a single fruiting tree) and 35 on 11 October 2020. Highest counts at other sites in the New Territories are 15 at Kam Tin on 17 May 2016 and 13 at San Tin on 24 September 2015, and elsewhere nine at Pui O (Lantau) on 9 July 2015, eight at Kowloon Tsai Park on 22 May 2019, six at Victoria Park (HK Island) on 25 March 2019 and five on Po Toi on 2 September 2010.

Compared to the 1990s, the population appears to be stable in the northern New Territories, but there are signs that the spread of closed-canopy shrubland is causing a distributional decline elsewhere. Asian Koel was recorded in 40.1% of 1 km grid squares in the breeding season survey of 1993-1996, but in only 27.3% of squares in the breeding survey of 2016-2019. Though differences in methodology between the two surveys may be a factor, the decline is considered to be genuine and is most marked on the islands of HK, Lantau and Lamma and in extreme eastern parts of the New Territories.

Despite being known to occur close to HK (Swinhoe 1860, Vaughan & Jones 1913), there were no published records of Asian Koel in HK until Hutson (1930a,b) listed it as a summer visitor breeding from April to August, though without specifying any localities. It was subsequently reported from Lam Tsuen Valley on 23 December 1933 and Pok Fu Lam on 21 February 1940 (Herklots 1934, 1940), including a sighting of 12 on the first date. Records from the late 1950s to the late 1990s indicate that it was generally widespread and in some years also locally common. Carey et al. (2001) regarded it as the commonest and most widespread of the cuckoos in HK and gave a peak count of ten at Mui Wo on 14 May 1994.

Its present-day status in Guangdong seems little changed from its historical status. In the early 1900s, it was considered a summer visitor, only rarely remaining to winter on the coast, with main arrival in March and autumn passage most apparent in October (Vaughan & Jones 1913).

BREEDING

Brood parasitism of Black-necked Starling previously observed in nearby parts of Guangdong (Swinhoe 1861, Vaughan and Jones 1913), was first reported in HK in 1931 with the discovery of an egg in a Black-necked Starling nest on 26 April and three young birds in another nest on 30 June (Hutson 1931). Since then, there have been multiple records of up to four dependent juveniles with a single pair of Black-collared Starlings in attendance between 11 April and 4 November. Juveniles have also been observed apparently being attended by two other species - Oriental Magpie (five records, April-June) and Red-billed Blue Magpie (three records, May and August).

BEHAVIOUR, FORAGING & DIET

An arboreal species that can be surprisingly secretive when not vocalising. In suboptimal habitat with dense foliage (e.g., forest or closed-canopy shrubland) its presence may only be revealed by nocturnal vocalisations recorded by static recorders.

In the breeding season, mainly from March to June, males sing for long periods day and night (mainly pre-dawn and early morning) and in fine weather or rain, often from the top branches of a tree, and can also be seen in bands of up to six chasing each other and sometimes even fighting. Song can be heard at other times of year also, but least of all from September to December.

Especially in autumn, but also in other seasons, birds of both sexes congregate to feed in fruiting trees. Among the parasitic cuckoos, Asian Koel is one of only several species whose diet consists mainly of fruit (Payne 1997). The fruit of Ficus superba, which is produced in crops up to five times per year in HK in all months except May (Thrower 1988), appears to be a particular favourite at Mai Po where the tree is very common. Other fruit taken in HK include those of Syzygium cumini, Arenga engleri, Livistona chinensis (Corlett 1994, Corlett and Ko 1995), Archontophoenix alexandra, Cinnamomum camphora, Melia azedarach, F. microcarpa, F. virens (So 1998), Carica papaya, Cleistocalyx operculata and mulberry Morus sp. Livistona chinensis is said to be the most favoured fruit in HK by Corlett and Ko (1995), who also state that in HK Koels can swallow fruit up to 17.5 mm whole and rapidly regurgitate seeds.

RANGE & SYSTEMATICS

Following the split of the forms from Sulawesi south to Australia, the species as currently constituted is widely distributed in south and southeast Asia east to China and south to Sumatra, Java, Borneo and the Philippines; birds in the east of the range winter to Borneo (Payne 1997). Five subspecies are recognised, including chinensis in Indochina and southern China and harterti on Hainan. The subspecies chinensis breeds across south China from Yunnan to Zhejiang and Jiangsu, and north to southeast Gansu, southern Shaanxi and Henan, with recent reports north also to Beijing (Birding Beijing 2022) and Liaoning.

CONSERVATION STATUS

IUCN: Least Concern. Population trend stable.