Justification Recent records of this species suggest that it is likely to have an extremely small and fragmented population which is rapidly declining owing to extensive habitat loss. It is therefore listed as Critically Endangered.

Family/Sub-family Oriolidae

Species name author Ogilvie-Grant, 1894

Taxonomic source(s) Sibley and Monroe (1990, 1993)

Identification 20 cm. Medium-sized, green and yellow oriole. Olive-green head and upperparts, olive-brown wings, yellow underparts. Large, heavy dark grey bill, dark red iris, dark grey legs. Similar spp. White-lored Oriole O. albilorus has white lores, shorter tail and shorter, more slender dark red bill. Voice Three calls have been recorded: a lsightly descending whistle lasting 0.5 s and repeated at intervals of 1-2 s; a higher, rising whistle repeated at similar intervals, and a harsh rolling call, not unlike a cricket repeated at 2 calls/s in a long series¹.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

50-249

decreasing

90,000 km²

Yes

Range & population Oriolus isabellae is endemic to Luzon in the Philippines. It is known from three localities in Bataan province and five in the north-east of the island. Eleven birds were collected near San Mariano in the Sierra Madre mountains in 11 days in 1961, indicating that it may not have been particularly rare in suitable habitat. However, in the north-east it has been recorded recently at just three localities (in Quirino province and Cagayan province, and in 2003-2006 at Ambabok and nearby Dunoy, Isabela province^1,2), despite an increasing number of fieldworkers attempting to locate it. There have been no observations in Bataan since 1947 and surveys in relatively undisturbed forest along the eastern coast of the Sierra Madre in 2006 failed to locate the species². This indicates considerable rarity and that its distribution is probably patchy.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: It frequents the canopy and middle storeys of forests, especially thick bamboo forest, but also forest edge, from 50-440 m. Constraints on its distribution and relative abundance are unknown, but it appears to tolerate secondary growth. It was recently observed in mixed-species flocks in fruiting trees.

Threats It may be a lowland specialist and lowland forest destruction is assumed to be its primary threat. Since the 1930s, forest cover in the Sierra Madre has declined by 83% and by the late 1980s only 24% of Luzon was estimated to remain forested, with most remaining areas under logging concession. There is virtually no forest left near Disulap, a key historical site, and one of the recent records was from a degraded forest tract of only 100 km², isolated from the Sierra Madre forests and offering no long-term prospects for the species. Competition with the closely related White-lored Oriole O. albiloris may impact this species¹.

Conservation measures underway Ambabok, where the species was recorded in 2003 and 2004, is located within the Northern Sierra Madre Natural Park (NSMNP), though there is no active law enforcement in this area. The Bataan Natural Park/Subic Bay protected area, which supports up to 50 km² of forest, probably encompasses one of the historical localities. Plans are scheduled for exploratory surveys in 2007 of the eastern side of the NSMNP upstream of the Palanan River, although this is above the recorded altitudinal range of the species².

Conservation measures proposed Conduct extensive surveys, particularly in bamboo forests, around historical sites in Bataan, the Mariveles Mountains and Mt Cetaceo, around Mansarong, and also Diffun (Quirino Province) where it has recently been reported. Propose key sites found for formal protection. Lobby for active on-the-ground protection of the NSMNP. Raise awareness among local people and local government about the species in an effort to implement conservation measures.

References Collar et al. (1999). 1. van Weerd and Hutchinson (2004). 2. M. van Weerd in litt. (2007).

Further web sources of information

Fully detailed species accounts from the Threatened birds of Asia: the BirdLife International Red Data Book (BirdLife International 2001), together with new information collated since the publication of the Red Data Book

Text account compilers Phil Benstead (BirdLife International), Jeremy Bird (BirdLife International), Geoffrey Davidson (Malaysian Nature Society), Pete Davidson (BirdLife International), Matt Harding (BirdLife International), Nic Peet (BirdLife International), Andy Symes (BirdLife International)

Contributors Merlijn van Weerd

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Andy Symes (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Oriolus isabellae. Downloaded from http://www.birdlife.org on 10/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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