NT
Taiwan Green-pigeon Treron formosae



Justification

Justification of Red List category
This species has a relatively small population size (estimated to number fewer than 2,000 mature individuals). There is currently no evidence for a continuing decline and its largest subpopulation (in Taiwan, China) is thought to be stable (slow declines are precautionarily suspected from its smaller population in the Philippines). Accordingly, its extinction risk is currently considered relatively low, however its small population size makes it vulnerable to future declines. Accordingly it is listed as Near Threatened.

Population justification
The global population of this species has not reliably been estimated. In Taiwan (China) it is believed to breed on only two small islands: Green Island and Orchid Island, with birds disappearing from the mainland during the breeding season (but a few birds apparently remaining on Taiwan year-round: eBird 2023). While the area of these two islands is small (15 and 47 km2 respectively) the species is described as not uncommon (Rueng-Shing Lin and Cheng-Ching Chiu in litt. 2023); nonetheless, Lin et al. (2016) reconciled that the total population size was still likely to be fewer than 1,000 mature individuals. On the Batanes islands (Philippines), the population size has not been estimated but applying equivalent densities as those observed on Taiwan, the population may number between 250-1,000 mature individuals. Overall therefore, the population is estimated as 1,250-2,000 mature individuals. This estimate is also congruent with the values of Brazil (2009), who suspected the population numbered between 200-2,000 mature individuals.

Trend justification
Formerly considered to be declining quite rapidly owing to habitat loss and hunting. However, forest loss in this species' range is now minimal: <1% in the three generations (13.8 years; Bird et al. 2020) to 2021 (Global Forest Watch 2022, based on data from Hansen et al. [2013] and methods disclosed therein). Hunting is a minimal threat in Taiwan but a greater one on the Babuyan and Batanes islands (Allen et al. 2006) and may be driving slow population declines. Consequently, the global population of this species is precautionarily suspected to be declining. The rate has not been quantified but is likely to be slow.

Distribution and population

T. formosae (as defined following the taxonomic change, and incorporating filipina) occurs on Lanyu Island and Chinese Taiwan, Batan, Calayan, Camiguin Norte and Sabtang (Philippines). It is rare on Taiwan, China and uncommon and local on the Batanes (BirdLife International 2001, Gibbs et al. 2001, Allen 2020).

Ecology

Breeds only on small islands, thus in the breeding season restricted to lowland (and often fairly degraded) forest. In the non-breeding season, moves to Taiwan's montane forests where it occurs up to 2,000 m (Gibbs et al. 2001, Lin et al. 2016). There are some records from Taiwan in all months, thus some/few (non-breeding) birds may remain on the island year-round.

Threats

Historically forest clearance and degradation was a key threat to this species, but remote sensing data indicate that over the past three generations this has been minimal. Consequently, the only threat thought capable of causing population declines is hunting and this is probably an issue only in the Philippines (see Allen et al. 2006).

Conservation actions

Conservation Actions Underway
None are known, but the species occurs in numerous protected areas in Taiwan, China. 

Conservation Actions Proposed
Survey to assess population size. Regularly monitor at certain sites throughout its range to determine population trends. Investigate the extent of hunting by local residents. Where relevant, control hunting where possible, perhaps using awareness campaigns. Protect significant areas of suitable forest across its altitudinal range.

Identification

c. 33 cm. A stocky green pigeon with a short tail, lacking any bright yellow tones in the plumage. The species has a dull orange cap contrasting with green face and neck and bold reddish-purple carpal patch. Similar spp. T. permagnus lacks the orange on the head and has a much duller carpal patch, contrasting little with the rest of the upperparts; it also has a longer tail. White-bellied Green Pigeon, which also occurs on Taiwan, has a white or pale yellow belly and bright yellow tones on the face. T. formosae also has a much plainer tail. Voice. A 'weird, prolonged cry remarkably like a child in pain' (Gibbs et al. 2001).

Acknowledgements

Text account compilers
Berryman, A.

Contributors
Taylor, J., Martin, R., Mahood, S., Symes, A., Everest, J., Benstead, P., Lin, R. & Chiu, C.


Recommended citation
BirdLife International (2024) Species factsheet: Treron formosae. Downloaded from https://datazone.birdlife.org/species/factsheet/taiwan-green-pigeon-treron-formosae on 25/02/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org on 25/02/2024.