Little known Oriental bird: Bornean Bristleheadby Simon Colenutt, OBC Bulletin 35, June 2002 The Bornean Bristlehead Pityriasis gymnocephala is endemic to the lowland forests of Borneo. It has been classified as Near Threatened (1) by BirdLife International based on its restricted range and the disappearance of its lowland forest habitat. The Bornean Bristlehead is a medium-sized (c. 25 cm) bird whose distinctive features are its massive hooked black bill and the short, yellowish to orange outgrowths of skin (3-4 mm long) on the crown which give the bird its English name. Other prominent features are its red face, throat, neck and thighs. The rest of the plumage is blackish, although in flight a white patch is visible in the wing. The sexes differ in that the female has red spots on the flanks, which are reduced or absent in the male. Juveniles have black rather than red thighs and red rather than grey ear coverts, and have fewer red feathers on the head and breast. In addition, the eye-ring is red and the head 'bristles' are undeveloped. The phylogenetic relationships of the species, supported by genetic evidence (2) place it as a close relative of the Australian Cracticids (magpies and butcherbirds) of the genera Cracticus, Gymnorhina and Strepera. Others(3) have placed the species within an enlarged Corvidae, with the Bristlehead in the tribe Artamini alongside Australian Butcherbirds (Cracticus), Australasian Magpie (Gymnorhina), Currawongs (Strepera), Woodswallows (Artamus), and Peltops (Peltops).
The species is widespread in Borneo from 0-600 m, but has also been reported at 1000-1200 m from Maliau, Sabah.(4) Witt & Sheldon (5) listed 62 sites from which the species had been recorded, to which the following can now be added; Lambir Hills National Park (Sarawak),(11) Lingga (Sarawak), Samunsam Wildlife Sanctuary (Sarawak), Tawau Hills National Park (Sabah), Ulu Temburong (Brunei), and Sepipong Reserve (Brunei). It is described as common in the secondary and peat swamp forests of southern Brunei, and as particularly common in the Anduki Forest Reserve (Brunei).(5) Generally speaking though, the Bristlehead is an uncommon species, for example, in the Danum Valley, one of its strongholds, six days of dawn to dusk observation between 2-8 November 1998 resulted in the sighting of one group of six birds and another of two birds (JN). Observations in Similajau during 1986 and 1995 suggest that the species is patchily distributed in the park.(7) It is probable that groups range over a wide area but that during breeding these movements are more localised. Although considered a bird of primary forest, the Bristlehead is found in a range of wooded habitats including disturbed primary forest, upland kerangas, coniferous forest, Shorea albida peat swamp, and degraded coastal swamp forest (DM). Bristleheads were observed by Western Foundation of Vertebrate Zooology (WFVZ) near Gomantong caves (Sabah) in old logged forest that had been severely burned during the El Niño drought. They have also been observed in Acacia groves adjacent to primary forest at Sepilok (Sabah) (KI). At Selipong Reserve (Brunei Bay), flocks have been reported from a large area of unspoilt mangrove. They are frequently recorded in secondary or partially logged forest, in clearings, along forest edge and roadsides, possibly due to a higher abundance of invertebrates in these locations. Their occurrence in the Danum Valley, Sarawak, is unpredictable, suggesting that birds may wander large distances in search of food, and prolonged observations of a group of 3-6 birds at distance of 700-800 m has suggested this.(7) However, its appearance in the Danum Valley has been described as seasonal, indicating that some altitudinal movement may occur.
Very little appears to be known of the breeding habits of the species. Flocks of Bristleheads have been observed carrying nesting material in May 1982 at Brumas (Sabah). A female collected at Brumas (Sabah) on 18 May 1982 had enlarged ova and ruptured ovarian follicles suggesting recent egg laying. Specimens collected at Sapagaya (Sabah) on 5 August 1983 and at Quoin Hill (Sabah) on 4 October 1962 had oviduct eggs, and the latter bird also had a well-defined brood patch.(5) An egg, measuring 31 x 25 mm, found in an oviduct of a specimen collected on 8 October 1896 was described as being 'pure white sparingly marked all over with large round and oval bright brown and slaty-grey spots of various sizes, the majority forming an irregular ring at the larger end'.(8) This range of dates suggests that the species may have a protracted breeding season. Its affinities to the Australian Cracticids suggest that it may build a cup-nest constructed of sticks and grass. The distinctive calls of the Bristlehead are heard more frequently than the bird itself is seen. Feeding groups call to one another in a near continuous manner. It produces a variety of noises, the most frequently heard of which are a nasal, whining contact call and a constantly uttered 'pit-pit-peeoo' interspersed with a corvid-like chatter. Calls are described as being nasal and highly distinctive. Other calls noted include a single loud whistle that each bird in the group utters in the space of 2-3 seconds. Most of the diet appears to be taken by gleaning leaves, twigs and tree trunks. Birds will occasionally make short flights to pounce on settled insects and sally-gleaning has been noted on a number of occasions. Amongst recorded prey items, lepidopteran larvae, orthopterans, coleoptera (one stomach contained many brenthidae (9)), cockroaches, arachnids and other large insects seem to be the most frequently taken. Large insects are dismantled after being braced against a branch; the wings and legs of larger insects are discarded. Fruit seems to be taken relatively infrequently but birds have been noted feeding on small olive to plum-sized fruit (IR). Bristleheads are almost always encountered in mixed sex flocks of 6-10 individuals, although the occasional pair is not unknown. It is an active canopy species that occasionally descends to the sub-canopy, c. 40-60 m above the ground (MS). They possibly move in flocks, even when nesting. On occasions, birds have been noted feeding in canopy emergents.(10) Members of the flock have been seen to spread across an area of up to 20 m radius (MS), although other observers have reported that individuals stay within close proximity of each other (JN). They have been noted feeding on large horizontal limbs, on which they move along in an ungainly manner with heavy sideways hops and bounds whilst calling loudly. Indeed, they have been described as moving in a woodpecker-like manner. They will ascend lianas by hopping upwards and turning 180 degrees with each hop, when they appear rather tit-like and they rarely stay long on any one branch (NA). Although infrequently recorded, they have been seen to cross open spaces, e.g. rivers (JN). Often the flock is accompanied by other large forest species, such as Black Magpie Platysmurus leucopterus, Malkohas, Babblers, Drongos, Trogons, Checker-throated Woodpecker Picus mentalis, Olive-backed Woodpecker Dinopium raflesii, and Hornbills. It is possible that at times Bristleheads may be flock leaders and Checker-throated Woodpeckers have been observed following Bristleheads.(7) The Bornean Bristlehead is an enigmatic species favouring the forest canopy and for this reason it has proved very difficult to photograph. The two photographs reproduced here were taken in 2000 and are thought to be the first known of the species. The photographer, Chris Artuso, was positioned on a ridge near the W10 mark on the famous Danum Valley grid system - one of the best places to see the species. The bird was part of a five-strong group moving through the canopy in the direction of the photographer. The ensuing commotion, combined with the birds' prominent red heads, made them surprisingly easy to pick up. They seemed to prefer prominent perches, where they would 'squat' for several minutes, making somewhat jerky head gestures as though trying to peer past obstacles to get a better look at the observer, before hopping off to look for another, similar perch. The individual in these photographs eventually approched to within very close range, perhaps lured by the foraging potential of the tall stump seen in the photo, and did not seem at all wary of the presence of the photographer. Acknowledgements References
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