Asian enigmas: Four odd 'thrushes'
by N.J. Collar from BirdingASIA 1, June 2004.
Expect the unexpected was Heraclitus's advice, and it applies particularly well to biomolecular studies of the modern age. DNA is telling us more and more unexpected things about the relationships of birds. Who among us would ever have thought that White-bellied Yuhina Yuhinazantholeuca (now Erpornis zantholeuca) has nothing to do with yuhinas or even babblers (Cibois et al. 2002), or that Hume's Ground-jay (now Groundpecker) Pseudopodoces humilis is a ground-jay-mimicking titmouse (James et al. 2003)? For many of us it is especially interesting to discover from such work whether single species in their own genus - what one might call "taxonomalies" - are really as anomalous as they appear to be. Among the many such oddities that Asia holds are four species traditionally placed in the thrushes: Grandala Grandala coelicolor, Geomalia Geomalia heinrichi, Sulawesi Thrush Cataponera turdoides and Fruithunter Chlamydochaera jefferyi.
The Grandala is perhaps the most bizarre of the four. The male is glistening purplish-blue with black wings and tail, the female dark brown with white streaking and wing-patch. A rather nomadic denizen of the high Himalayas, breeding up to 5,500 m, its most striking features are its wing-shape - very long wing-tip and rather short secondaries, producing a swallow-like effect - and its gregariousness, wheeling in flocks of tens or hundreds in pursuit of aerial insects, and hopping starling-like across short-grass slopes in search of terrestrial ones. Seebohm (1881) and Ripley (1952) both thought it was closest to Nearctic bluebirds Sialia, but Oates (1890), Oberholser (1919) and Vaurie (1955) demurred. Oberholser put it in its own family, Grandalidae, but the general assumption is that it is a highly modified chat (our photo of a female inclines me to agree). Taxonomists struggle to know where to put the turdine genera Myophonus and Monticola, both of which are characterised by blue plumage, and for the moment I think it makes sense to group Grandala informally with those taxa (but Heraclitus's warning predicts a very different outcome following DNA sampling!).
Geomalia is only slightly less bizarre and, because it is so elusive, much more mysterious. This was one of the great discoveries of the remarkable German explorer Gerd Heinrich during his time in Sulawesi in 1930-1931 - the first one he saw hopped momentarily into the entrance of his tent while he was busy on the evening's skinning - his description of the encounter (Heinrich 1932) puts me in mind of West Africa's Picathartes. A large chestnut-breasted dark brown passerine, with a heavy, laterally compressed bill, lanky, spindly legs surrounded by long fluffy plumage, long, graduated tail and very short, arched wings, it resembles nothing so much as a cross between a thrush and a Garrulax babbler. But Stresemann (1931), in naming the species (and despite adopting Heinrich's suggestion Geomalia, which implies a clear link to Malia, another Sulawesi endemic genus then assumed to be timaliine), emphatically rejected the babbler connection (my translation):
A large, long-tailed ground bird, of the stature of a Janthocincla maxima [Giant Laughingthrush Garrulax maximus], but, as shown by the structure of the legs, toes, wings and tail feathers, in no way related to the Crateropodidae [babblers]. Most probably Geomalia is best placed in the group of brachypterygine birds [shortwings] (and indeed close to Heinrichia), unless one prefers to establish it in its own subfamily (Geomaliinae).
So White & Bruce (1986) were mistaken in saying that Stresemann (1931) placed Geomalia in the babblers and called it a "completely isolated genus"; he did this only after a decade of further reflection (but without explaining his change of mind), in Stresemann & Heinrich (1939-1941). However, he still maintained its link to Heinrichia, which he also placed as a babbler (by extension along with the closely allied Brachypteryx). If Geomalia and the shortwings are distantly related, however, it is not feasible for modern authorities to follow the conventional treatment of the latter as thrushes - White & Bruce (1986) and Coates & Bishop (1997) do this - without taking Geomalia with them. The fact that juveniles possess spotted underparts (babbler young have no juvenile plumage) ought, I suppose, to be clinching evidence that Geomalia is not a babbler - a rare and perhaps unique photograph of a live bird just about confirms this, and also suggests a rather strong turdine posture - but I remain firmly on the fence.
The name "Sulawesi Thrush" suggests the matter of its relationships is fully resolved, but this is far from true. Hartert (1896), in erecting the genus Cataponera, while admitting its thrush-like appearance (hence "turdoides"), thought it a babbler related to Garrulax, and its black eyebrow is a notable timaliine feature (e.g. Striated Laughingthrush Garrulax striatus, Grey-throated Babbler Stachyris nigriceps, various fulvettas and parrotbills) but unknown among thrushes. Meyer & Wiglesworth (1898) commented that it is very like certain blackbirds in appearance, though the shape of its wing, as well as the peculiar superciliary stripe of black, at once shows that it has no very real near affinities with Merula or Turdus.
On the other hand Heinrich found that in both voice and juvenile plumage it was distinctly turdine, so Stresemann & Heinrich (1939-1941) placed it with the thrushes. Coates & Bishop (1997) seem to settle the matter: "Behaves like a typical thrush (Turdus)... flushes with typical thrush-like calls from the understorey". Yet recently Jon Riley commented to me (in litt.) that, on the few occasions he saw it, "it behaved very like a tree babbler or scimitar babbler: very active, restless movements, bouncing around in the lower storey"; and Richard Thomas tells me he had a similar impression during his encounter. There is, moreover, a curious single-paragraph paper by Desfayes (1967) which, while failing to consider the evidence in Stresemann & Heinrich (1939-1941), restated the case for what he called the "Black-browed Babbler": "its thick, rounded rufous tail, bill shape and general proportions are unlike any Turdinae. Its similarity to Garrulax impresses one at once... [including] a tendency of having bare orbital skin". Aaaagh! Back to the fence.
The Fruithunter is one of the special wonders of Borneo, ranking alongside the outrageously weird Bristlehead Pityriasis gymnocephalus and a handful of other avian genera endemic to the island (but far fewer than Sulawesi!). The species, the most notable discovery of John Whitehead on Mt Kinabalu and named, like the Philippine Eagle Pithecophaga jefferyi, for his father, was initially considered to be a triller (Sharpe 1887), and this view, with the occasional notion that it might be an oriole, persisted for nigh on a century until Ames (1975) pointed out its turdine syringeal morphology, Ahlquist et al. (1984) found a DNA link to Turdus, and Olson (1987) noted its skeletal agreement with the thrushes and plausibly argued for its placement near (and even congeneric status with) the cochoas Cochoa. Even so, Sheldon et al. (2001) report on some strange attributes:
When sitting, their posture is pigeon-like, but when they congregate at berry trees, they act much like bulbuls. They also resemble laughingthrushes in some behaviors and often occur in pairs. Their flight is that of a campephagid, in that they dip their pointed wings in and out rather than flap.
Pigeon, bulbul, laughingthrush, cuckooshrike, oriole - what a bird! Even its English name is no longer quite accurate. In extreme drought conditions in May-June 1998 a number of birds around the Kinabalu Park headquarters were seen to forage amidst flowerbeds on the introduced snail Bradybaena simillaris (Smythies & Davidson 1999) - a very thrush-like thing to do.
For all its harlequin guises, the Fruithunter is the most straightforward of four enigmas here, given the convergent results of the internal morphological and biomolecular analyses to which it has been subject. And clearly there is a lesson to be learnt from it - that appearances are deceptive, and behaviours are very unstable guides to taxonomic position. It is fascinating to contemplate what similar syringeal, skeletal and chemical studies will make of the Grandala, Geomalia and Sulawesi Thrush; but this is not to exclude the possibility that intensive field study might produce new evidence to bear on all three forms. The two latter remain so baffling that one is tempted to speculate whether they, and perhaps even Malia Malia grata, are isolated relics of a group of birds that share both timaliine and turdine features, ancestral to both and long marooned on the riddlingly interesting and appallingly neglected island of Sulawesi. When is someone going to set themselves up in the highlands there and spend some serious time getting to grips with these extraordinary animals?
References
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