Detailed Species Accounts from The

Threatened Birds of Asia: The BirdLife International Red Data Book

Editors N. J. COLLAR (Editor-in-chief), A. V. ANDREEV, S. CHAN, M. J. CROSBY, S. SUBRAMANYA and J. A. TOBIAS

Maps by RUDYANTO and M. J. CROSBY

Principal compilers and data contributors ■ BANGLADESH P. Thompson ■ BHUTAN R. Pradhan; C. Inskipp, T. Inskipp ■ CAMBODIA Sun Hean; C. M. Poole ■ CHINA ■ MAINLAND CHINA Zheng Guangmei; Ding Changqing, Gao Wei, Gao Yuren, Li Fulai, Liu Naifa, Ma Zhijun, the late Tan Yaokuang, Wang Qishan, Xu Weishu, Yang Lan, Yu Zhiwei, Zhang Zhengwang. ■ HONG KONG Hong Kong Bird Watching Society (BirdLife Affiliate); H. F. Cheung; F. N. Y. Lock, C. K. W. Ma, Y. T. Yu. ■ TAIWAN Wild Bird Federation of Taiwan (BirdLife Partner); L. Liu Severinghaus; Chang Chin-lung, Chiang Ming-liang, Fang Woei-horng, Ho Yi-hsian, Hwang Kwang-yin, Lin Wei-yuan, Lin Wen-horn, Lo Hung-ren, Sha Chian-chung, Yau Cheng-teh. ■ INDIA Bombay Natural History Society (BirdLife Partner Designate) and Sálim Ali Centre for Ornithology and Natural History; L. Vijayan and V. S. Vijayan; S. Balachandran, R. Bhargava, P. C. Bhattacharjee, S. Bhupathy, A. Chaudhury, P. Gole, S. A. Hussain, R. Kaul, U. Lachungpa, R. Naroji, S. Pandey, A. Pittie, V. Prakash, A. Rahmani, P. Saikia, R. Sankaran, P. Singh, R. Sugathan, Zafar-ul Islam ■ INDONESIA BirdLife International Indonesia Country Programme; Ria Saryanthi; D. Agista, S. van Balen, Y. Cahyadin, R. F. A. Grimmett, F. R. Lambert, M. Poulsen, Rudyanto, I. Setiawan, C. Trainor ■ JAPAN Wild Bird Society of Japan (BirdLife Partner); Y. Fujimaki; Y. Kanai, H. Morioka, K. Ono, H. Uchida, M. Ueta, N. Yanagisawa ■ KOREA ■ NORTH KOREA Pak U-il; Chong Jong-ryol, Rim Chu- yon. ■ SOUTH KOREA Lee Woo-shin; Han Sang-hoon, Kim Jin-han, Lee Ki-sup, Park Jin- young ■ LAOS K. Khounboline; W. J. Duckworth ■ MALAYSIA Malaysian Nature Society (BirdLife Partner); K. Kumar; G. Noramly, M. J. Kohler ■ MONGOLIA D. Batdelger; A. Bräunlich, N. Tseveenmyadag ■ MYANMAR Khin Ma Ma Thwin ■ NEPAL Bird Conservation Nepal (BirdLife Affiliate); H. S. Baral; C. Inskipp, T. P. Inskipp ■ PAKISTAN Ornithological Society of Pakistan (BirdLife Affiliate) ■ PHILIPPINES Haribon Foundation for Conservation of Natural Resources (BirdLife Partner); N. A. D. Mallari, B. R. Tabaranza, Jr. ■ RUSSIA Russian Bird Conservation Union (BirdLife Partner Designate); A. V. Andreev; A. G. Degtyarev, V. G. Degtyarev, V. A. Dugintsov, N. N. Gerasimov, Yu. N. Gerasimov, N. I. Germogenov, O. A. Goroshko, A. V. Kondrat’ev, Yu. V. Labutin, N. M. Litvinenko, Yu. N. Nazarov, V. A. Nechaev, V. I. Perfil’ev, R. V. Ryabtsev, Yu. V. Shibaev, S. G. Surmach, E. E. Tkachenko, O. P. Val’chuk, B. A. Voronov. ■ SINGAPORE The Nature Society (Singapore) (BirdLife Partner); Lim Kim Seng ■ SRI LANKA Field Ornithology Group of Sri Lanka (BirdLife Affiliate); S. Kotagama; S. Aryaprema, S. Corea, J. P. G. Jones, U. Fernando, R. Perera, M. Siriwardhane, K. Weerakoon ■ THAILAND Bird Conservation Society of Thailand (BirdLife Partner); U. Treesucon; R. Jugmongkol, V. Kongthong, P. Poonswad, P. D. Round, S. Supparatvikorn ■ VIETNAM BirdLife International Vietnam Country Programme; Nguyen Cu; J. C. Eames, A. W. Tordoff, Le Trong Trai, Nguyen Duc Tu.

With contributions from: S. H. M. Butchart, D. S. Butler (maps), P. Davidson, J. C. Lowen, G. C. L. Dutson, N. B. Peet, T. Vetta (maps), J. M. Villasper (maps), M. G. Wilson Recommended citation BirdLife International (2001) Threatened birds of Asia: the BirdLife International Red Data Book. Cambridge, UK: BirdLife International.

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ISBN 0 946888 42 6 (Part A) ISBN 0 946888 43 4 (Part B) ISBN 0 946888 44 2 (Set)

British Library-in-Publication Data A catalogue record for this book is available from the British Library

First published 2001 by BirdLife International

Designed and produced by the NatureBureau, 36 Kingfisher Court, Hambridge Road, Newbury, Berkshire RG14 5SJ, United Kingdom

Available from the Natural History Book Service Ltd, 2–3 Wills Road, Totnes, Devon TQ9 5XN, UK. Tel: +44 1803 865913 Fax: +44 1803 865280 Email [email protected] Internet: www.nhbs.com/services/birdlife.html

The presentation of material in this book and the geographical designations employed do not imply the expression of any opinion whatsoever on the part of BirdLife International concerning the legal status of any country, territory or area, or concerning the delimitation of its frontiers or boundaries. Threatened birds of Asia

ISABELA ORIOLE Oriolus isabellae

Critical — Endangered C1 Vulnerable A1c; A2c; C2a

This species is subject to extensive habitat loss and is believed to have a small, rapidly declining and fragmented population, which qualifies it as Endangered.

DISTRIBUTION The Isabela Oriole is endemic to Luzon in the Philippines, where it has repeatedly been stated to be known from just two disjunct provinces, Isabela and Bataan, in spite of evidence available in two museums since 1960 of its occurrence in a third. New records (although see Collar 1998b) have now indicated it in two further localities and one further province, as follows: ■ PHILIPPINES Luzon (western) Dinampan (untraced), Bataan, November and December 1904 (four specimens in BMNH, FMNH, USNM); Lamao river, 5 km inland from Manila Bay, Bataan, 50 m, November 1947 (Gilliard 1950; specimen in AMNH); Mariveles, Bataan, February and March 1902 (McGregor 1903; male in FMNH; see Remarks 1); (eastern) Ipil (at 75–150 m) and Tapel, Gonzaga, Cagayan, April 1960 (six specimens in DMNH, FMNH); Mansarong, Baggao, Cagayan, September 1994 (van der Linde 1995); “Molino”, a tobacco estate at or near present-day San Mariano, Isabela, May 1894 (Whitehead 1899a, Dickinson et al. 1991, Danielsen et al. 1994; see Remarks 2), with further records coming from Disulap, 140 m, at San Mariano, May 1961 (11 specimens in AMNH, PNM; also Poulsen 1995); reported 15 km south of Diffun, between Baguio and Don Mariano Perez, Quirino, near the Nueva Vizcaya border, 440 m, December 1993 (Gamauf and Tebbich 1995).

POPULATION The description of this species as uncommon (Dickinson et al. 1991) appears to have been a notable euphemism, given that it had not then been seen since 1961 and was being considered by fieldworkers within its anticipated range as possibly the first Luzon endemic close to extinction (Mallari and Jensen 1993, Poulsen 1995; see Remarks 3). Nevertheless, the fact that the Disulap records in 1961 concerned the collection of 11 birds in as many days (6–17 May) suggests that the species was then not particularly rare in the right habitat (perhaps seasonally conspicuous), and it is perfectly possible that this is still the case. Nevertheless, the failure of an increasing number of observers to find the species down to the present day equally suggests that it may be unpredictably patchy in occurrence. It was looked for without success at Disulap on several occasions, 1991–1992, but by that time most of the forest in the area had been cleared (Poulsen 1995).

ECOLOGY Habitat The species occurs in the canopy of forest—especially thick bamboo forest, where the type specimen was obtained (Whitehead 1899a; see Remarks 4)—and forest edge, singly, in pairs, small groups and mixed flocks (Dickinson et al. 1991), but the constraints on its distribution and relative abundance have not been identified or even suggested. The Lamao (Bataan) bird, November, was shot 8 m up in a tree in secondary forest (“border of regional forest” on AMNH label) on the riverbank in company with Black-shouldered and Blackish Cuckoo-shrikes Coracina morio and C. coerulescens (Gilliard 1950). The parent and offspring (see Breeding below) at Disulap, May, were low (1 m up) in climbing bamboo in low secondary forest at the edge of an open field (AMNH label data). The Quirino bird, 1993, was at the edge of a remnant area (1 km2) of secondary forest near a new banana

2392 Oriolus isabellae plantation, in a mixed-species flock near a fruiting tree (Gamauf and Tebbich 1995). The Mansarong bird, 1994, was in a large mixed-species flock feeding in fruiting trees along a logging road (van der Linde 1995). The suggestion that the species is known from around 600 m (Delacour and Mayr 1946) was apparently slightly overstated: all records under Distribution where elevation is known are from 50 to 440 m.

LUZON 4

P A C I F I C O C E A N

6 7

CATANDUANES

MARINDUQUE MINDORO

The distribution of Isabela Oriole Oriolus isabellae (sequence not as in text): (1) Tapel; (2) Mansarong; (3) Ipil; (4) San Mariano; (5) Diffun; (6) Lamao river; (7) Mariveles. Historical (pre-1950) Fairly recent (1950–1979) Recent (1980–present)

2393 Threatened birds of Asia

Food Nothing is recorded, but the 1993 and 1994 records were of birds in flocks associated with fruiting trees, and it may well be that this species is at least partly frugivorous. Breeding Five out of the six specimens taken in April 1960 in Cagayan province had active gonads (DMNH, FMNH label data). Three of five males taken in May 1961 had enlarged testes, one of five females was “breeding”, and one young bird (female) was being fed by another of the adult females (AMNH, PNM label data). Clearly breeding activity is strong in the period April–May. Migration It is not known if this species undertakes any form of seasonal or elevational displacement.

THREATS The reasons for the very patchy distribution of this species are not clear, but it could be that it is a lowland forest specialist. There is virtually no forest left at Disulap, an area judged to be near the type locality and the site at which the species was last collected, in 1961 (Poulsen 1995), while the site of the 1993 rediscovery was in a degraded area of only 100 km2, fully isolated from the Sierra Madre forests and offering no long-term prospects for the species (Gamauf and Tebbich 1995). Despite the claimed conservation status of forest at Lamao (see next section), Gilliard (1950) was “greatly saddened at the destruction which has been visited on this important laboratory forest in recent years”. Lowland forest destruction throughout Luzon is a major hazard to all species confined below 1,000 m, and this bird appears to be particularly linked to lower-lying areas. On the other hand, all twentieth-century records in which the habitat has been recorded are from secondary forest, which perhaps suggests some flexibility in the species.

MEASURES TAKEN The Isabela Oriole has been recorded at Mansarong in Northern Sierra Madre Natural Park, a CPPAP site (see Appendix). According to Gilliard (1950) the forest in which the Lamao specimen was collected was soon after reserved within Lamao National Park, as an extension of a protective ordinance dating from 1903 “ostensibly as a permanent station for the study of problems relating to Philippine forests” (but see Threats). Although this national park apparently no longer exists (DENR 1993), part of the area may be covered by Bataan Natural Park/Subic Bay (see Appendix) and the species should be searched for in this area.

MEASURES PROPOSED Apart from the areas targeted for conservation above, the species has been recorded, albeit historically, at two “key sites” (Mt Cetaceo and Mariveles Mountains; see Appendix). These should be formally designated as protected areas under the NIPAS process and thoroughly surveyed so that the species’s status can be assessed. Any conservation strategy for Luzon should take into consideration the distribution and requirements of several threatened species endemic, or near-endemic, to the island (see equivalent section under Green Racquet-tail Prioniturus luconensis).

REMARKS (1) McGregor (1903) provided measurements of a female taken in February at this locality; this skin was presumably retained in Manila and lost in the destruction of the Bureau of Science during the Second World War. He obtained the male at the same site and virtually the same time as a male Celestial Monarch Hypothymis coelestis (see Remarks 1 under that species). (2) The type locality of this bird has not been fixed more precisely than Isabela province (Ogilvie Grant 1895a). However, the date of the type is 4 May 1894 (Dickinson et al. 1991), and the account and map of its collector’s travels (Whitehead 1899a: 82–83) reveal that his arrival on “a tobacco estate in the province of Isabella, at the foot of the eastern Cordillera of North Luzon” (from the map this is “Molino”, clearly close to present-day San Mariano as noted by Dickinson et al. 1991), was on the previous day, 3 May 1894. It is therefore reasonable to restrict the type locality to San Mariano, as already implied

2394 Oriolus isabellae by Poulsen (1995) and by the map, based on the BirdLife Biodiversity Project data (ICBP 1992, Stattersfield et al. 1998), in Danielsen et al. (1994:33); moreover, the fact that Whitehead reached “Molino” by boat from Aparri and collected the type the next day is a strong indication that the elevation was not great—one might guess not more than 300 m. (3) Collar et al. (1994) attributed to Dickinson et al. (1991) the information that the species had not at that time been seen since 1961, and this was evidently the source of the same attribution by Gamauf and Tebbich (1995). This was in error; there is nothing on this subject in Dickinson et al. (1991), and the correct source was in fact Poulsen (1995), at that stage in press. (4) The fact that Whitehead stipulated bamboo but only collected a single bird suggests that he may have seen more than the published or specimen record indicates.

2395