Oriental Cuckoo Cuculus optatus


Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
Densities of 0.1-0.5 singing males/km2 have been recorded in Russia (Hagemeijer and Blair 1997). Assuming an equal sex ratio and 20-40% occupancy of its EOO breeding range, the population size is suspected to number 500,000-5,000,000 mature individuals; the true figure is likely to be at the highest end of this estimate given that the European breeding population is estimated at 120,000–155,000 calling or lekking males, or 240,000–310,000 mature individuals (BirdLife International in prep.). National population estimates include: c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in China; c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Taiwan; c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Korea; c.100-100,000 breeding pairs and c.50-10,000 individuals on migration in Japan and c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Russia (Brazil 2009).

Trend justification
Remoting sensing data on tree cover lost indicate that c.6-8% of forest cover has been lost from the species's breeding range over the past three generations (11 years; Global Forest Watch 2021). Its reliance on undisturbed forests for breeding is unknown but the majority of its host species are moderately forest-dependent, and the present species is reported to be outcompeted by C. cuculus in more open habitats in parts of its range (Erritzøe et al. 2012). Forest loss may be anticipated to accelerate with forest fires in Siberian forests becoming more frequent (and intense) as a consequence of climate change. This should continue to be monitored closely. Forest loss is occurring at a similar rate (5-7% over three generations) in this species's non-breeding range, which may equally be causing some decline; however, this species has been noted wintering in open and heavily degraded habitats, and so these declines are thought to be less significant. Overall, the species is suspected to be declining at a rate of 1-10% over three generations.

Distribution and population

This species has an extremely large range. It breeds from European Russia (with singing males occasionally recorded as far west as Finland) north to the Arctic Circle in Siberia, to the Pacific coast including Kamchatka, the Kuriles and Sakhalin, south to Kazakhstan and Mongolia through Altai to north of c.32°N in China. Also throughout the Korean Peninsula, and Japan south to Honshu. Similarly widespread on passage and in winter, but almost total overlap with the morphologically near-identical C. saturatus confounds accurate mapping. Occurs on passage in Hainan, Chinese Taiwan and through the Japanese archipelago, including Ryukyu. Winters in Indochina, Borneo, Java, the Philippines, throughout Wallacea, the Bismarck Archipelago, the Solomon Islands, New Guinea (including Waigeu) Micronesia (Palau and Yap) and north and east Australia. Vagrants have reached New Zealand, New Britain, the Aleutian Islands and Alaska.


Breeds in mixed coniferous-deciduous, larch taiga and broadleaf forests, usually at elevations below that of C. cuculus. Also in wooded hill country and orchards and open areas (Payne 1997, Erritzøe et al. 2012). This species parasitizes a wide range of passerines, with genera including Phylloscopus, Locustella, Anthus, Horornis, Ficedula and Prunella, and so expected to occur anywhere its hosts can be targeted (Payne 1997, Erritzøe et al. 2012). Densities of breeding birds in Russia were higher in pine and spruce forest (0.4-0.5 males/km2) than in spruce and aspen forest (0.1 males/km2) (Hagemeijer & Blair 1997). On passage and in winter, occurs in all manner of habitats included open woodland, plantations, forest edge and clearings, and gardens; typically at lower elevations (Erritzøe et al. 2012).


This species is suspected to be declining at a slow rate because of forest loss (6-8% over three generations; Global Forest Watch 2021) in its breeding range, principally as a consequence of forest fires in Siberia. These fires are predicted to increase both in extent and intensity in line with climate change. Forest loss in its non-breeding range may also be a threat, although this species appears tolerant of degradation on its wintering grounds.

Conservation actions

Conservation Actions Underway
Species has a vast range and occurs in numerous protected areas.

Conservation Actions Proposed 
Forest loss in Siberia should continue to be monitored using remote sensing data.


32-33 cm. A typical Cuculus cuckoo with grey upperparts and head, densely black-barred pale underparts, and a conspicuous yellow eye-ring. The sexes are similar, but the female has neck and upper breast washed rufous. Females also sometimes occur in hepatic morph which is rufous with dark barring on head, upperparts, wings and tail. In all plumages, very similar to, and more or less inseparable from, C. saturatus, except for distinct vocalisations.


Text account compilers
Berryman, A.

Bird, J.

Recommended citation
BirdLife International (2023) Species factsheet: Cuculus optatus. Downloaded from on 01/06/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 01/06/2023.