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 Yuhina zantholeuca (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. |
