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Little known Oriental bird - Chestnut-headed Partridge: 2

This matches well with the type description (2) and Delacour and Jabouille also note a good deal of variation in their specimens from Bokor, particularly in the strength of the black barring on the upperparts. They attributed this as probably due to age (3). From these observations, it can be concluded that, although unassigned, the published plate in King et al. is of nominate cambodiana (14), whilst that in Lekagul and Round is, of course, diversa (10).

The plumage of diversa is as follows:

Forehead, lores, supercilium, lower ear-coverts, throat and neck to side of upper neck pale brown, throat feathers narrowly edged with black, sometimes with white centres. This pattern increases on the lower throat to form a black (sometimes interspersed with white) neck band across the lower throat. Crown, nape and upper ear-coverts dark tawny brown. Breast rich chestnut. Mantle pale brown, not boldly barred black, with only narrow black terminal bars to feathers. Undertail-coverts described by Riley as white, edged with dusky (6); however, photographs show buffy vent with white undertail similar to cambodiana.

As with Delacour and Jabouille's description of cambodiana (3), Riley noted considerable variation amongst specimens of diversa, noting particularly that 'no two of the females are alike' (5).

On the limited published data on biometrics from eight specimens of cambodiana and five specimens of diversa, the latter is generally shorter in the wing, but there are no significant differences.

Calls of the two forms are still undescribed, and would no doubt be useful in resolving the taxonomic issues. Dymond tape-recorded what was almost certainly diversa on Khao Soi Dao in February 1998, and notes the call as 'a whistled couplet 'tu-u-huÖtu-u-hu' i.e. a short 'tu-u' followed by an accented 'hu', repeated at the usual Arborophila pace, but without any appreciable ascending pitch or urgency' (N. Dymond in litt.).

Based on the plumage differences, the question has been posed as to whether or not these two forms might be better treated as full species? (8,9,10) To this end, McGowan et al. treat the two forms separately for conservation purposes and recommend 'taxonomic clarification should assess whether cambodiana and diversa are best treated as species or subspecies' (10). It is not within the scope of this review to tackle this question and further taxonomic work is required. However, in his review of the genus Arborophila, Johnsgard could see no reason for accepting more than a single species of another member of the genus, Scaly-breasted Partridge A. charltonii, 'considering the variability of various other Arborophila forms' (16). This should certainly be borne in mind when considering the taxonomy of the Chestnut-headed Partridge.

Conservation
Chestnut-headed Partridge is listed by Collar et al. as globally threatened in the Vulnerable category (8). McGowan et al. also list A. c. cambodiana as Vulnerable, but place A. c. diversa in the more highly threatened, Endangered, category (9). Both sites from which diversa has been recorded in Thailand are included in protected area networks: Khao Soi Dao Wildlife Sanctuary and Khao Sabap National Park (17). However, Khao Sabap has been selectively logged and Khao Soi Dao is threatened by small-scale encroachment and hunting (17). In Cambodia the situation is much more alarming. Bokor is designated as a national park as is Kirirom (where the species may occur); however, large-scale illegal logging is occurring in both parks, particularly Bokor (18). Indeed, in early 1998 a European Commission consultant working in Bokor stated that 80% of the park was already affected by logging (19), and this has continued unabated since (20). In addition, the fact that the only recent records come from a wildlife market indicates that the species may also be threatened by hunting. However, Arborophila species in Laos show remarkable levels of resilience to high levels of snaring and other forms of hunting (Will Duckworth in litt.), so it is unclear how serious a threat this may be.

On the basis of these potentially serious and imminent threats facing the population of cambodiana, and the lack of current knowledge of this form, it is recommended that it should currently be considered as under similar or greater threat than diversa, whose populations exist in the comparatively well-enforced protected areas of Thailand.

Conclusion
A great deal needs to be discovered about the status of the two forms of Chestnut-headed Partridge. In particular, nothing is currently known about whether either form is even found in the 300 km of the Cardamom mountain range between the known sites. If the species is in this region, which form is it that occurs? The region itself is listed as a Secondary Endemic Bird Area (s085) by BirdLife International (21), yet it has hardly been investigated ornithologically. What little is known is that there are also interesting, and as yet unresolved, forms of several other species present, including White-necked Laughingthrush Garrulax strepitans ferrarius, White-tailed Robin Myiomela leucura cambodiana and Fire-breasted Flowerpecker Dicaeum ignipectus cambodianum (10,17). However, this area in Cambodia is far from untouched by loggers. Recent work by the World Bank and the NGO Global Witness indicates that, at the current rate of extraction, Cambodia's forestry resources may be economically depleted within five years (18,22). In addition, World Bank maps of both legal forest concessions and illegal logging areas show that the remaining areas of the Cardamoms are suffering among the heaviest logging pressure (22,23). Add to that the ongoing security problems in the area and landmines, and it is unlikely that much significant ornithological work will be possible in the immediate future, and by the time it is, who knows what will be left?

Acknowledgements
I thank Philip Round for providing references and further information on A. c. diversa and discussing and commenting on the contents of this note, Uthai Treesucon for further information and permission to use his photographs, Nick Dymond for further information on his record from Khao Soi Dao and Tim Inskipp for providing copies of references listed in Mlíkovsky, J. and Inskipp, T. P. (in prep.) Annotated checklist and bibliography of the birds of Indochina. I am grateful to Will Duckworth, Frederic Goes and Joe Tobias for providing comments on this manuscript. And finally, I thank Klaut Randy and David Ashwell for asking me to come and identify a 'pair' of partridges.

References

1. Delacour, J. (1928) QuatriËme expÈdition en Indo-chine. L'Oiseau 9: 257–269, 301–308.
2. Delacour, J. and Jabouille, P. (1928) Twenty-one new birds from Indo-China. Bull. Brit. Orn. Club 48: 125–136.
3. Delacour, J. (1929) On the birds collected during the fourth expedition to French Indo-China. Ibis (12)5: 193–220, 403–429.
4. Warren, R. L. M. (1966) Type-specimens of birds in the British Museum (Natural History). Vol. 1: Non-passerines. British Museum (Natural History), London.
5. Riley, J. H. (1930) Descriptions of three new birds from Siam. Proc. Biol. Soc. Wash. 43: 189–192
6. Delacour, J. and Jabouille, P. (1931) Les oiseaux de l'Indochine française. Vol. 1. Exposition Coloniale Internationale, Paris.
7. Riley, J. H. (1938) Birds from Siam and the Malay Peninsula. US Natn. Mus. Bull. 172: 63.
8. Collar, N. J., Crosby, M. J. and Stattersfield, A. J. (1994) Birds to watch 2. BirdLife International, Cambridge.
9. McGowan, P. J. K., Dowell, S. D., Carroll, J. P. and Aebischer, N. J. (1995) Partridges, Quails, Francolins, Snowcocks and Guineafowl. IUCN, Gland.
10. Lekagul, B. and Round, P. (1991) A guide to the birds of Thailand. Saha Karn Bhaet, Bangkok.
11. Round, P. D. (compiler) (1994) Recent reports. Bird Conserv. Soc. Thailand Bull. 11(6): 13.
12. Engelbach, P. (1938) Note sur quelques oiseaux du Cambodge. Oiseau et R.f.O. 8: 384– 394.Thomas, W. W., (1964) Unpublished typescript on the birds of Cambodia.
13. King, B. F., Dickinson, E. C. and Woodcock, M. W. (1975) A field guide to the birds of South-East Asia. Collins, London.
14. Davison, G. W. H. (1982) Systematics within the genus Arborophila Hodgson. Federated. Mus. J. 27: 125–134.
15. Johnsgard, P. (1988) The quails, partridges and francolins of the world. OUP, Oxford.
16. Round, P. D. (1988) Resident forest birds in Thailand: their status and conservation. ICBP Monograph 2, Cambridge.
17. Global Witness (1998) Going Places – Cambodia's future on the move. Global Witness, London.
18. Poole, C. M. (1998) Pillaging the park. BBC Wildlife. 16(3).
19. The Cambodia Daily. Park officials intend to force clandestine loggers to pay fines. 6/11/98: 9.
20. Stattersfield, A. J., Crosby, M. J., Long, A. J. and Wege, D. C. (1998) Endemic bird areas of the world. BirdLife International, Cambridge.
21. Development Alternatives International (1998) Findings and recommendations of the log monitoring and logging control project. Main report. Final edition. DAI. Bethesda, MD.
22. Kingdom of Cambodia (1998) Cambodia National Environmental Action Plan 1998–2002. Ministry of Environment, Phnom Penh.