Little known Oriental bird: Chestnut-headed Partridge
by Colin M. Poole, from OBC Bulletin 30, November 1999.
On 25th January 1998 I was asked to identify a pair of partridges bought some days earlier at Sre Khlong, a Cambodian wildlife market situated on Highway 4 in Kompong Speu province, south of Phnom Penh. The 'pair' proved to be one Scaly-breasted Partridge Arborophila charltonii and one Chestnut-headed Partridge A. cambodiana. The latter is a globally threatened species, endemic to the Cardamom mountain chain of south-west Cambodia and south-east Thailand, and this was the first Cambodian record since 1936. Both birds had apparently been caught in the vicinity of Kirirom National Park, from where much of the wildlife at Sre Khlong is sourced. If so, this record would represent a range extension for the species. I was able to take several photographs, which I believe to be the first ever taken of this species. Unfortunately, both birds subsequently died and were disposed of. However, it prompted me to carry out a search of the literature to find out what was known of the history and status of Chestnut-headed Partridge.
Chestnut-headed Partridge was discovered in December 1927 when eight or nine specimens were collected from the Cambodian mountain of Bokor by P. Jabouille and Willoughby Prescott Lowe, members of the Fourth Franco-British Expedition to Indochina (1-4). It was described the following year by Delacour and Jabouille (2).
Bokor was a French colonial hill station situated on a plateau at 1,000 m at the southern end of a mountain range known as the Cardamom, Elephant or Kravanh Mountains, stretching 330 km north-west to the Thai border, and this was the first-ever ornithological expedition to the area. At the time, Delacour described both the slopes and the plateau as being 'unspoiled', the slopes were covered with tall damp forest, whilst the summit plateau was 'very peculiar, the trees being rather low and stunted, with an abundance of orchids and other epiphytes' (3). It was in the latter area, on the plateau, that Chestnut-headed Partridge was collected.
In 1928, Delacour and Jabouille described Chestnut-headed Partridge as 'a very distinct species' (2) and closer to Red-breasted Partridge A. hyperythra of Borneo than any of its continental congeners (1,3). However, in November 1930, Riley described a new species of partridge, A. diversa, on the basis of a single specimen collected in January 1930 by Dr H. M. Smith from semi-evergreen forest at 300 m at Khao Sabap (also known as Namtok Phliu National Park), Chanthaburi, Thailand (5) – the opposite end of the Cardamom mountain range. At the time, Riley had no specimens of Chestnut-headed Partridge available for comparison and his specimen did not agree with the published description, although he notes it as 'evidently closely allied' (5). Smith, on seeing the plate of Chestnut-headed Partridge published by Delacour and Jabouille in 1931 (p. 50) (6), later retracted A. diversa as a separate species, and in 1938 he described the two forms as subspecies, A. c. cambodiana and A. c. diversa. 7 This is their current taxonomic position, although there is still considerable debate over this view (8,9,10).
Since the time of these early collectors there have been very few records of either form. Following his first expedition, Smith returned to Khao Sabap in November 1933 and collected a further four specimens of diversa (7). The subspecies was then unrecorded until March 1966 when B. F. King collected two specimens from hill evergreen forest at 1,129 m altitude on Khao Soi Dao Tai (the more southerly, and the higher, of the two Soi Dao peaks) (P. D. Round in litt.). Although listed by Collar et al. as 'probably common' in Khao Soi Dao, with 'several recent records' (8), I have only been able to trace two records in the wild since. The first is of a single bird seen by R. Harwood in May 1994. (11) The second is of two birds recorded by N. Dymond in February 1998 in montane evergreen forest, at approximately 1,400 m (N. Dymond in litt.). It has seemingly been unrecorded from Khao Sabap since Smith's last expedition of 1933, and there are no other records from Thailand. However, in 1988 at least two birds were recorded and photographed by Uthai Treesucon in captivity at the Pong Namron Captive Breeding Centre of the Wildlife Conservation Division, which is situated at the foot of Khao Soi Dao (p. 50) (P. D. Round in litt.). In 1995, McGowan et al. estimated the population of A. c. diversa to be 100-1,000 and that the 'wild population could be in the low hundreds', whilst that of cambodiana was estimated at more than 100 (9). However, little indication is given as to how, and from what evidence, these figures were derived, and they are therefore best treated with caution.
The situation for cambodiana is even less well-known. Following the collection of the original specimens, Bokor was visited in 1935 and 1936 by P. Engelbach, who was resident in the nearby town of Kampot. He found it to be 'relativement trés commune' (relatively very common) between 400–1,000 m and, somewhat surprisingly, recorded it as being easier to approach than other partridge species, often venturing out into open areas. On 14th June one year he saw a pair with an unrecorded number of young chicks (12). This behaviour pattern, unusual for any Arborophila species, has not been reported before or since for either form. However, the fact that in 1927 at least eight birds were collected in two days may indicate that it was, at least then, relatively easy to find. The assertion of Thomas in 1964, that the species was 'common and conspicuous in the Elephant chain' (13), is presumably based on Engelbach, as he cites no personal records and there appear to be no other records since 1936, or from any other locality than Bokor, until the bird I was shown in January 1998.
Plumage I took the following description of the captive cambodiana: Forehead, lores, supercilium, throat and neck to side of upper neck rich chestnut-brown, flecked with black over the supercilium and sides of neck. Crown, nape and ear-coverts black, black connecting from the crown to the rear of the ear-coverts behind the eye. Breast and mantle mid-brown, with black median and terminal bars to feathers on back and sides of lower neck.
Flank feathers black with white triangular centres. Belly through to vent pale brown/buff, white undertail. Scapulars and coverts pale brown, those towards the outer-wing being darker and mottled black and those closer to the inner-wing being strikingly pale with black sub-terminal marks and chestnut tips. Secondaries mid-brown, mottled black. Primaries black. Eye black. Bill black. Legs pink.
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).
Plumage-wise the two forms differ significantly. A study of the plate in Lekagul and Round (10), examination of photographs (p. 50), reference to the original description of A. diversa (5), and subsequent discussion (7), all reveal several plumage differences between cambodiana (above) and diversa.
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.
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.
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?
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.
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