|Western Whistler Pachycephala occidentalis, adult male at Wungong Gorge near Perth|
Given that WA birds were previously not even separated as a subspecies, this was a little surprising – but this is a group with a long history of splits. The ‘Golden Whistler’ complex was once lumped as one bloated species, famously supposed to have the most subspecies of any bird in the world. It hit its high point in 1956 when 56 subspecies were recognized, many now split off as full species, including Mangrove Golden Whistler and various island forms (and the list is growing - there are now 67 taxa in the superspecies complex). The core species (termed ‘Australian Golden Whistler’ by IOC) was eventually whittled down to three mainland Australian subspecies, one on Tasmania (glaucura), one each on Lord Howe and Norfolk islands (the IOC currently notes ‘Norfolk Whistler’ xanthoprocta as another possible split), and a one in New Guinea (balim) that taxonomists have struggled to find a home for (though recent studies suggest it belongs instead with Yellow-throated Whistler).
Since that revision Western Australian birds have been listed as the buff-bellied subspecies fuliginosa, also extending across to South Australia’s Eyre Peninsula, the gulf region and south of the Murray to around the Victorian Grampians. Both Schodde & Mason  and HANZAB  suggested that south-west birds could be recognized as ‘regional form’ occidentalis, but fell short of seperating it as a subspecies. HANZAB noted the “tendency for both sexes from sw. Aust. to be slightly paler”.
‘Slightly paler’ pretty much sums it up. Compared to the closest and most similar Australian Golden Whistler subspecies, the residual fuliginosa, Western Whistler has:
- Slightly narrower yellow collar
- Slightly paler back
- More lemon-yellow (not sulphur-yellow) breast, grading to a whiter vent
- Lighter grey tail with a narrower black subterminal band
|Western Whistler male at Victoria Dam - a good site for view this species (see previous blog post)|
|Western Whistler at Wungong Gorge. Males have a lighter grey tail with a narrower black band than Golden Whistler.|
FEMALE & IMMATURE MALE
- Lighter, neutral mid-grey (not grey-green) back
- Even dorsal toning, lacking bi-toned contrast between greyer head and tail, and greenish back as in fuliginosa (as in this example).
- Paler buff underparts (though Johnstone & Storr’s Handbook of WA Birds  states female underparts are paler in the north, and illustrates a distinctly pale “female (northern form)”, implying that tone of the buff underparts are clinal north to south as per Glogers rule).
|Western Whistler female at Donnelly River. Note the pale buff belly, and even grey toning of the dorsum with minimal tonal contrast between the back and head.|
|Western Whistler, first immature, showing retained rufous juvenile plumage. Denmark, Western Australia. (Photo 2010 CC BY 2.0, via Wikimedia commons by Flickr user butapa)|
Given these minor differences, it is fair to call Western Whistler a cryptic species. The split only came to light during a series of recent genetic studies of the whole ‘Golden Whistler’ complex (Jønsson et al 2008, 2014; Andersen 2014) [4-6], the latter of which by chance included a few eastern fuliginosa in addition to WA samples. The most recent study by Joseph et al.  (published only on 22 Dec 2014 – the IOC move fast!) nailed the split with a bigger comparative sample of eastern fuliginosa. All of these studies independently conclude from both nuclear and mitochondrial DNA that Western Whistler is no more (and probably less) closely related to eastern forms of Golden Whistler, than it is to Mangrove Golden Whistler (~2.5% mtDNA divergence from both).
|The ND2-ND3 mtDNA tree determined by the most recent and most completely sampled study by Joseph et al. 2014 . Note WA and SA/Vic forms previously lumped under one subspecies fuliginosa are widely separated genetically.|
|The Australian Museum female Western Whistler specimen (AM 0.18570) likely to be designated the lectotype for the new species, from Ramsay’s (1878) original King George Sound syntypes (Image © 2014 Australian Museum, via types collection in ala.org.au, reproduced here under Fair Use terms).|
The name Western Whistler (recommended by the authors of Joseph et al., and adopted by IOC) is disappointingly plain, but probably appropriate in this case as a direct translation of occidentalis (Latin = western). However a check of atlas data shows this is not strictly a WA endemic, with a few records just east of the WA/SA border. This is unsurprising since the thin strip of mallee along the edge of the Great Victoria Desert is continuous across the border, thus the southern edge of treeless Nullarbor Plain proper separates the two species by about 200km.
|Atlas data from ala.org.au, showing Western Whistler records (red circles) extend just across the WA/SA (dotted line). The closest Golden Whistler records are about 200km to the east, c. 60km W of Yalata. The dense cluster of circles to the left is at Eyre Bird Observatory, where Western Whistler is common. (Image and data © ala.org.au, reproduced here under Fair Use terms)|
Where to find Western Whistler
Western Whistler can potentially occur anywhere southwest of a line from approximately Shark Bay to Cocklebiddy, though they are generally commonest in wetter forested areas with a thicker understory (e.g. the karri and tall jarrah forests of the Darling R and deeper southwest). They are also found in coastal vegetation, especially in gullies with cover from peppermint trees, and in most well-wooded reserves through the southern wheatbelt. In drier inland and northern parts it is much less common and tends to be associated with thickets of sheoak, which often surround at the base of granite outcrops. It is not common in the suburbs of Perth, with only occasional records presumably of dispersing birds. It only becomes regular on the Swan coastal plain further south, from about Lake Cooloongup near Rockingham. Thus sites in the Darling Range (e.g. Victoria Dam, Ellis Brook, Bickley Brook, Bungendore) represent the closest places to Perth to look for it, though Rottnest Island also has a resident population in remnant woodland areas.
 Schodde R & Mason I (1999) The Directory of Australian Birds: Passerines. A taxonomic and zoogeographic atlas of the biodiversity of birds of Australia and its territories. CSIRO Publishing.
 Marchant S. & Higgins PJ, et al. (eds) (1990-2006). Handbook of Australian, New Zealand and Antarctic Birds. (7 vols). Oxford University Press, Melbourne.
 Johnstone RE and Storr GM (1998-2004). Handbook of Western Australian birds (2 vols). Perth, Western Australian Museum.
 Jønsson K et al (2008). Molecular phylogenetics and diversification within one of the most geographically variable bird species complexes Pachycephala pectoralis/melanura. J Avian Biol 39: 473-478
 Jønsson et al (2014). Evidence of taxon cycles in an Indo-Pacific passerine bird radiation (Aves: Pachycephalalidae). Proc R Soc B 281:20131727.
 Andersen et al. (2014). Molecular systematics of the world's most polytypic bird: the Pachycephala pectoralis/melanura (Aves: Pachycephalidae) species complex. Zoological Journal of the Linnean Society 170: 566-588
 Joseph L, Nyári A, Andersen MJ (2014). Taxonomic consequences of cryptic speciation in the Golden Whistler Pachycephala pectoralis complex in mainland southern Australia. Zootaxa 3900: 294-300