Oriental Cuckoo Cuculus optatus 東方中杜鵑
Category I. Passage migrant, uncommon in spring, scarce in autumn.
IDENTIFICATION
Mar. 2016, Martin Hale. Adult.
38-40 cm. Oriental Cuckoo is very similar in appearance to its three regional congeners, Himalayan Cuckoo C. saturatus, Eurasian Cuckoo and Lesser Cuckoo. In size it is the same as the first of these, slightly smaller than the second and clearly larger than the third. In plumage it is considered indistinguishable at all ages and in both morphs from Himalayan Cuckoo, though the two can usually be separated if wing measurements are known. Grey-morph birds are similar in upperpart colour to Lesser Cuckoo and Common Cuckoo of the subspecies bakeri but darker-mantled than Common Cuckoo of the subspecies canorus and subtelephonus. They can also be distinguished from Common and Lesser Cuckoos by their more widely-spaced and noticeably broader blackish barring on the belly and by a broad white band that extends across the underwing from the axillaries to the inner primaries (Kennerley and Leader 1991); some individuals also have buffy undertail coverts with broad dark bars. Grey morph females are washed rufous on neck and upper breast. Hepatic females are barred on the head and rump. Adults of both sexes have a yellow eye-ring and brownish iris.
Oct. 2015, Michelle and Peter Wong. Juvenile.
Juveniles of the hepatic morph are similar to hepatic adult females in being closely barred on the head and throat, more broadly so on the mantle and back, but the scapulars, coverts and flight feather have narrow pale fringes.
VOCALISATIONS
The song is a low-pitched note repeated 2-4 times that may be introduced by a rapid short series of the same and/or a grating cough.
DISTRIBUTION & HABITAT PREFERENCE
Almost 60% of records are from Po Toi and Mai Po NR, with the remainder from fairly widespread parts of the New Territories (mainly in the lowlands), HK Island, Kowloon, Lantau, Lamma, Tung Ping Chau and Lung Kwu Chau. Favoured habitats are fung shui woods and stands of trees on the edge of marshes, fishponds, farmland or other open areas, and occasionally also forest, shrubland and urban parks.
OCCURRENCE
Records of five individuals of known wing length that were identified as this species together with the absence of any records of Himalayan Cuckoo has meant that sight records of birds showing the appearance of Oriental/Himalayan Cuckoo are treated as Oriental Cuckoo C. optatus. The five individuals positively identified as Oriental Cuckoo were all caught in ringing sessions at Mai Po NR (16 September 1989, 17 April 1992, 5 May 2002, 26 April 2008, 17 April 2010), with the identification based on measurements provided by King (2005). The wing lengths of two other individuals trapped or found injured at Mai Po NR (11 April 2009, 17 April 2010) were in the overlap zone between Oriental Cuckoo and Himalayan Cuckoo.
On this basis, Oriental Cuckoo occurs in two periods, from 22 March to 21 May and 28 August to 21 October (Figure 1). A high proportion of the total occur in April (49%), especially the second half of the month when numbers peak, and September (26%). Most reports are of single birds, occasionally two; the only higher counts are five on Po Toi on 9 May 1999 and six on Tung Ping Chau on 16 April 2016.
No great change in status is apparent since the 1990s. The first accepted records were single hepatic birds at Pak Nai on 30 September and Mong Tseng on 14 October 1978.
There are three further records of undetermined Oriental/Himalayan Cuckoo, all outside of the passage periods outlined above: a hepatic bird at Shek Kong Catchwater from 17 to 24 February 2010, a grey-morph bird at Lam Tsuen from 8 to 11 March 2016, and a hepatic bird on Po Toi on 4 July 2013. Photographs indicate that the latter bird was also present on Po Toi earlier in the spring of the same year, from 7 April to 2 May.
Reports of birds vocalising in HK are very rare. The only individual known to have been sound-recorded is a first-summer bird on a wooded hillside at Tai Mei Tuk between 29 April and 7 May 2008. The 3-note phrase it uttered lacked the short introductory note characteristic of Himalayan Cuckoo in southern China but was higher in pitch than Oriental Cuckoo in northwest China, Ussuriland and Hokkaido. Although the sonograms are inconclusive, it was considered by Carey and Lewthwaite (2012) to probably be a bird from the breeding population in Taiwan, whose taxonomic status is uncertain.
BEHAVIOUR, FORAGING & DIET
Like others in the genus, Oriental Cuckoos are secretive in habits. Most observations are of birds perched quietly in a tree; individuals are sometimes noted feeding in the canopy or, very occasionally, coming down to the ground in search of food. Caterpillars are the only food item noted in HK.
RANGE & SYSTEMATICS
The breeding distribution of Oriental Cuckoo is from west Russia east across Siberia to Kamchatka, south to Kazakhstan, the Altai mountains, Mongolia, northern China, Korea and Japan; it winters from southeast Asia to Australia (Payne 1997). The taxonomic status of the breeding population in Taiwan is uncertain. Payne (1997) treated it as part of saturatus, while Xia et al. (2016) concluded the population was optatus based on song characteristics.
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Figure 1.
Carey, G. J. and Lewthwaite, R. W. (2012). Vocalisations of an unidentified cuckoo at Tai Mei Tuk. Hong Kong Bird Report 2009-10: 302-309.
Kennerley, P. R. and Leader, P. J. (1991). Separation of [Eurasian] Cuckoo and Oriental Cuckoo. Dutch Birding 13: 143-145.
King, B. (2005). The taxonomic status of the three subspecies of Cuculus saturatus. Bull. B.O.C. 125 (1): 48-55.
Payne, R. B. (1997). Family Cuculidae (Cuckoos) in del Hoyo, J., Elliot, A. and J. Sargatal. Handbook of the Birds of the World, vol. 4: Sandgrouse to Cuckoos. Lynx Edicions, Barcelona, Spain.
Xia, C., W. Liang, G. J. Carey and Y. Zhang (2016). Song Characteristics of Oriental Cuckoo Cuculus optatus and Himalayan Cuckoo Cuculus saturatus and Implications for Distribution and Taxonomy. Zoological Studies 55: 38.
