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BirdingASIA 14 (2010): 23–2923 ID FORUM Malaysian Whistling Thrush Myophonusrobinsoni— field identification, distributionand conservation concerns DAVID N. BAKEWELL, LIM KIM CHYE, SHAHRUL ANUAR BIN MOHD SAH & M. A. MUIN According to BirdLife International (2003), theMalaysian Whistling Thrush Myophonus robinsoni is one of 20 restricted-range species confined tothe Sumatra and peninsular Malaysia Endemic BirdArea (EBA). It is one of only three speciesrecognised by BirdLife International as beingendemic to peninsular Malaysia, the others beingMalaysian Partridge Arborophila campbelli andMountain Peacock Pheasant Polyplectroninopinatum . However, the latter has now beenrecorded in southern Thailand (Wells 2007), soarguably forfeits its peninsular Malaysian endemicstatus.Despite its small range, Malaysian WhistlingThrush is currently rated as of Least Concern(BirdLife International 2010). In the notes onpopulation and range, the BirdLife commentarystates that ‘it is known from at least eight localities.There are recent records from at least three:Robinson Waterfall in the Cameron Highlands,Fraser’s Hill and the Malayan Nature Society BohTea Estate Centre’[ sic ]. However, this assessmentis called into question by the potential for fieldobservers to mistake the little-known, dull-plumaged dicrorhynchus race of Blue WhistlingThrush Myophonus caeruleus for MalaysianWhistling Thrush (Teo & Wee 2009, Bakewell et al . 2009). Wells (2007) states that dicrorhynchus Blue ‘is suspected (but still not proven) to occurabove the montane ecotone’. The commonly heldassumption has been that Blue and MalaysianWhistling Thrush occupy separate elevationalranges, and that identification can be determinedby elevation. This is despite the assertion of Lekagul& Round (1992) that throughout Thailand it occurs‘from lowlands to the highest elevations’. In recentyears, few have questioned the identification of whistling thrushes seen at montane hill stationsand they have been assumed to be Malaysian.Between April 2009 and July 2010, a study wasundertaken to discover reliable field criteria fordifferentiating Malaysian and dicrorhynchus BlueWhistling Thrush, to establish the extent to whichthe elevational ranges of Malaysian and Blueoverlap, and to estimate populations of Malaysianand dicrorhynchus Blue, particularly at the principalmontane localities of Cameron Highlands andFraser’s Hill. Whistling thrushes at hill stations The Department of Wildlife and National Parks(PERHILITAN) granted us a permit to trap andmeasure whistling thrushes between January 2009and January 2010. Three visits of 2–4 days eachwere made to both the Cameron Highlands andFraser’s Hill (Table 1). Mistnets were set up at likelysites for whistling thrushes at a variety of altitudesbetween 1,437 m and 1,942 m (CameronHighlands), and 979 m and 1,257 m (Fraser’s Hill).Early mornings were spent walking or drivingaround suitable areas, listening and looking forwhistling thrushes between 746 m and 1,995 m(Cameron Highlands) and 979 m and 1,305 m(Fraser’s Hill). Recorded calls of both species wereplayed in an attempt to elicit a response from anybirds present. Local people were shown picturesof whistling thrushes to ascertain whether theywere a familiar bird in the area. Table 1 . Details of site visits to hill-stations during the survey. Malaysian Whistling ThrushBlue Whistling Thrush Photo- Sound Seen/ Photo- Sound Seen/Location Dates Trapped graphed recording heard Trapped graphed recording heard Cameron Highlands24–27 April 200900001222Cameron Highlands8–11 September 200900001213Cameron Highlands5–7 May 201000000002Fraser’s Hill18–22 June 200900000101Fraser’s Hill8–11 October 200911110000Fraser’s Hill19–20 July 201001010000 24Malaysian Whistling Thrush Myophonus robinsoni— field identification, distribution and conservation concerns Perhaps surprisingly, in view of the frequentrecords of Malaysian Whistling Thrush andcorresponding paucity of claims of Blue WhistlingThrush from these two localities, Blue WhistlingThrush was overwhelmingly the predominantspecies observed. At Cameron Highlands, Blue wererecorded from eight localities (819–1,779 m) andMalaysian not at all. At Fraser’s Hill, Blue wasrecorded at Jeriau Waterfall (979 m) and the onlyMalaysian found during the survey were seen onseveral dates at the well-known ‘stake-out’ at thetop gate of the Gap–Fraser’s Hill road (1,221 m).The survey thus ended speculation over whetheror not a montane population of Blue WhistlingThrush exists in peninsular Malaysia and, in doingso, cast doubt on many previous sight records of Malaysian Whistling Thrush in the CameronHighlands and at Jeriau Waterfall, Fraser’s Hill. Field identification The smaller size of Malaysian compared with BlueWhistling Thrush is often highlighted in publishedliterature but, since the difference is apparently notvery large, only 15% according to measurements(Wells 2007), it is assumed that this may be difficultto judge. Emphasis therefore tends to be given toplumage features, for example the extent of metallicspangling or spotting and the presence or absenceof patches of bright blue in the plumage, as themain criteria to be used in separating these species.We suggest that this, coupled with lack of awareness of the plumage and range of the dicrorhynchus race of Blue Whistling Thrush, hasled to frequent misidentification of Blue WhistlingThrush as Malaysian. Plumage The appearance of whistling thrushes in the fieldis surprisingly variable. This is due, first, to theeffect of light on perceived colour. Sunlight shiningon a bird can highlight metallic areas and colour,making it look obviously spotted or scaled. Dulllight can make the same bird appear entirelyunmarked. Dark backgrounds tend to make a birdappear bluer. Conversely, a bird in shade or againsta lighter background can appear sooty-black oreven brownish. Second, feather wear can have astrong influence on appearance. Freshly moulted dicrorhynchus Blue appears well-spotted orspangled with metallic coloration. However, sincethe metallic coloration is on the feather edges andtips, once these wear away birds lack brightspotting or spangling and appear plain blue orblack.One of the most commonly quoted identificationfeatures of Malaysian is the presence of a brightblue ‘shoulder-patch’ caused by the metallic tipsto the lesser coverts. However, since dicrorhynchus Blue Whistling Thrush also shows this feature (andfurthermore, on both species these feathers areusually hidden beneath the scapulars), it isgenerally unhelpful for identification.The same is true of the metallic feathering onthe forehead, frontal band or supraorbital ridge—both species can show or lack this plumage feature,depending on the state of feather wear and the angleand intensity of the light.From our observations, the only plumagefeature which is useful in separating the two speciesis the presence of pale spotting on the mediancoverts. When present, this is a diagnostic fieldmark of Blue Whistling Thrush. However, absenceof this spotting is inconclusive, as worn BlueWhistling Thrushes often do not show any mediancovert spots. Bare parts Some Malaysian Whistling Thrushes show a slightlyyellow tinge to the orbital ring which is not shownby Blue. The colour of Malaysian’s bill isconsistently more orange-yellow than that of Blue.Neither of these characteristics is likely to be of much help in the field, but may be useful whenattempting identification from photographs. Size and structure Size and structure offer the best criteria fordistinguishing Malaysian Whistling Thrush fromBlue in the field. In spite of what publishedmeasurements suggest, Malaysian is a very muchlighter-bodied species than Blue, as indicated bythe weight of the only bird caught during the survey(111 g) being a mere 46% of the average weight of four dicrorhynchus Blue (240 g) caught. (In additionto the two dicrorhynchus Blue caught in theCameron Highlands, two were caught at a lowlandsite in the Kinta Valley, Ipoh.) Blue WhistlingThrush, particularly the dicrorhynchus race, is alarge thrush; Malaysian is more akin to a typical Turdus thrush in size.Structurally, Malaysian appears squatter thanBlue, with a shorter neck and a deeper and morerotund body (Plates 1, 2 & 3). Despitemeasurements which indicate that the tail isrelatively longer than Blue (Wells 2007, Robson2008), this is not always evident in the field. Thetail appears less ‘full’ than that of the Blue, asMalaysian tends to fan it less widely than does Blue.The most distinctive features of each speciesare the shape and proportions of the head and bill.The head of Blue often shows definite anglesbetween the forehead and forecrown, and betweenthe rear crown and nape. The bill is thick, heavy,rather blunt-tipped, and commonly strongly BirdingASIA 14 (2010)25 Plate 1 . Dicrorhynchus Blue Whistling Thrush in worn plumage. The plumage appears very similar to that of Malaysian Whistling Thrush, but note the vestigial paler tips to one or two median coverts. The structure is diagnostic of Blue, especially the angular headand heavy, parallel-sided, hooked bill. Cameron Highlands, 2 March 2008. Plate 2 . Malaysian Whistling Thrush. Note the compact, short-necked appearance, gentle head shape and tapered, Turdus -like billshape. Fraser’s Hill, 20 July 2010. D A V I D B A K E W E L L D A V I D B A K E W E L L hooked. The gape-flange often angles down fromthe line of the bill, giving the bird a fierceexpression. Malaysian Whistling Thrush, bycontrast, has a gentle, rounded head shape, and amore proportionate, less hooked bill, which isobviously slighter than that of Blue. The gape-flangemay either angle down from the line of the bill orcontinue in a straight line from it. In either case, itlacks the fierce expression of the Blue (Plate 4). Behaviour We tentatively suggest two aspects of behaviouras confirming the identification of MalaysianWhistling Thrush. First, when foraging, the headis frequently cocked, with the bill pointing upwardsat more or less a 45° angle, a characteristic alsonoted by Clement & Hathaway (2000). Second, bothspecies lift, lower and fan their tails rhythmically,but Malaysian tends to only half-spread its tailwhereas Blue fans its tail fully when performingthis action. Habitat Malaysian Whistling Thrushes are less likely tofrequent large, open streams than are Blue, and maymore often be found in montane forest away fromwatercourses, or near very small streams,particularly where these are in deep gullies. Theonly nests proven to belong to Malaysian were allfound in epiphytic tree-ferns attached to branchesover small mountain streams (Madoc & Allen 1952).Whistling thrushes frequenting or found nesting incaves, man-made structures (including culverts) ornear waterfalls are almost certain to be Blue. Voice The contact calls of whistling thrushes aredistinctive, although care should be taken to avoidconfusing them with the initial note of the two-toned song of Pygmy Wren Babbler Pnoepyga pusilla and the shorter call of Slaty-backed Forktail Enicurus schistaceus .Distinguishing one species of whistling thrushfrom another by call is, however, more challenging. Plate 3 . Scaled composite showing dicrorhynchus Blue, Cameron Highlands, 8 September 2009 (left) and Malaysian Whistling Thrush,Fraser’s Hill, 8 October 2009 (right) being held in the same hand, showing size difference. Note the yellowish orbital ring on thisMalaysian Whistling Thrush. Plate 4 . Composite image showing the bills of three different dicrorhynchus Blue Whistling Thrushes (left) and three differentMalaysian Whistling Thrushes (right). D A V I D B A K E W E L L D A V I D B A K E W E L L 26Malaysian Whistling Thrush Myophonus robinsoni— field identification, distribution and conservation concerns The principal differences between the commoncontact calls of the two species are shown in thespectrograms (Figures 1 & 2). Blue WhistlingThrush’s call is audibly modulated, starting higher,as if being forced out under pressure, and thensliding lower, sounding something like tsee-eee .Malaysian Whistling Thrush’s call is much moresingle-pitched, and starts with a slight raspingquality before becoming purer. The rasping startis difficult to transliterate, but the call sounds like chzzz-eeee . The call lasts slightly longer than thatof Blue, and seems to hang in the air rather thantail off abruptly.Such subtle differences require a sharp ear andexperience, as well as good listening conditions,but with practice can be useful in the field.Spectrograph analysis of recordings makesidentification simpler, as the downward inflectionof Blue or the more or less level tone of Malaysianshow up distinctly. What is the real status of MalaysianWhistling Thrush? BirdLife International cites eight localities wherethe Malaysian Whistling Thrush has been recorded.However, some sites—the ‘Malayan Nature SocietyBoh Tea Estate Centre’ [ sic ], Tanah Rata, Parit andRobinson Waterfalls, Gunung Batu Brinchang andCameron Highlands Wildlife Sanctuary (BirdLifeInternational 2001, 2010)—are better treated as onesite, the Cameron Highlands.Having taken possible duplication into account,we consider the species to have been recorded fromsix localities (Figure 3). Specimens have beencollected from: (1) Gn Menuang Gasing (alsoknown as Gn Nuang); (2) Gn Mengkuang Lebar(also known as Gn Menkuang Lebah, GnMengkuang); (3) Gn Ulu Kali (Genting Highlands);(4) Fraser’s Hill. All these are peaks lying on theborder between Selangor and Pahang at thesouthern end of the Titiwangsa Range. Additionalrecords of live birds are from: (5) The CameronHighlands (four birds netted near the summit of Gn Batu Brinchang and multiple sight records of birds at several locations); (6) Bukit Larut (MaxwellHill), in the Bintang Range, Perak (sight record)(BirdLife International 2001, McClure 1964).A record of three birds ringed during ten one-week netting operations in low ericaceous cloud-forest at Gn Batu Brinchang, Cameron HighlandsWildlife Sanctuary, Pahang, at c.480 m (1,574 ft)(BirdLife International 2001, Collar 2005, quotingMedway & Wells 1963), has the elevation incorrect.The srcinal document states ‘ten one-week nettingoperations were undertaken during four yearscovering most months, on the upper fifteen hundredfeet of Gn Brinchang (6,600 ft .)’ (Medway & Wells1963, italics added). This indicates that the birdswere actually trapped at 5,100 ft (1,554 m) orabove. All other records fall within an elevationalrange of 760–1,770 m (Robson 2008), 755–1,510 m(Clement & Hathaway 2000), or 850–1,700 m, withcore habitat possibly above 1,500 m (Wells 2007). Figures 1 & 2 . Audio spectograms of Blue and MalaysianWhistling Thrush contact calls. Figure 3 . Localities where Malaysian Whistling Thrush (MWT)has been recorded. For numbers see text above.Malaysian Whistling Thrush contact callBlue Whistling Thrush contact call BirdingASIA 14 (2010)27
