• 1 species on Sulawesi, Indonesia
• DR personal total: 1 species (100%), 1 photo'd

Recent genetic evidence has uncovered a number of completely unexpected relationships between birds. To learn that the vocal Donacobius of the Amazon Basin was a relict Old World grassbird was shocking, as were findings that certain "babblers" in the Himalayas were actually close relatives of New World vireos. But perhaps none have been more unexpected than the 2008 discovery that an obscure "whistler" in the undergrowth of montane forests on Sulawesi was actually a relict bombycillid — related to the waxwings and relatives. This bird is Hylocitrea (left, in a fine shot by Rob Hutchinson), which is usually called the "Olive-flanked Whistler" or "Yellow-flanked Whistler."

Spellman et al. (2008) published this finding in their study of the bombycillids. One of the authors, Rob Moyle, had found a tentative link between Hylocitrea and bombycillids in an exploratory molecular analysis. So a more detailed study of nuclear and mitochondrial genes was undertaken for all putative members of this group, including Hypocolius (an odd passerine from the Middle East) and Hylocitrea. The analysis showed that both Hypocolius and Hylocitrea belong among the lineage that gave rise to waxwings, silky-flycatchers, and the Palmchat of Hispaniola. Spellman et al. (2008) recommended that each of these be considered a subfamily of an enlarged Bombycillidae, but most recent authorities prefer to split Hylocitrea into its own family, consistent with prior treatments of Palmchat and Hypocolius.

The bird itself is an enigma. The Handbook of the Birds of the World included it among the whistlers (Pachycephalidae; Boles 2007) but had very little to say about it. In the introduction Boles (2007) mentioned that "The Mottled Whistler (Rhagologus leucostigma) and the Yellow-flanked Whistler (Hylocitrea bonensis) have primarily frugivorous diets, but it is questionable that this has any important phylogenetic significance." Maybe not, but we now know that Mottled "Whistler" of New Guinea is not a whistler, but is within a clade that includes woodswallows and African bush-shrikes, with its exact position still unknown (Norman et al. 2009). And we know that "Yellow-flanked or Olive-flanked Whistler" is not a whistler, but is a member of the bombycillid radiation. About all Boles (2007) says its that the bird is "little known," eats "berries and some arthropods", and "frequents middle storey and understorey," sometimes joining "mixed-species flocks."

Its range is restricted to higher elevations in Sulawesi, in moss forest usually above 2000m [~6500' elev.], but it can descend to lower elevations from time to time. It is best known from Lore Lindu and Dumoga-Bone National Parks. The mossy forest nature of its habitat shows nicely in these photos.

There are whistlers that frequent the same montane habitat, such as the endemic Sulphur-bellied Whistler Pachycephalus sulfuriventer, and until the genetic evidence, nothing about Hylocitrea caught anyone's attention. Coates & Bishop (1997) says that it is generally "inactive, inconspicuous and easily overlooked; seldom calls or sings." Behaviorally, it "can be tame;" Holmes (1996).

Coates & Bishop (1997) described the song as a "series of insistent, thin, high-pitched buzzy notes on the same pitch." Hmmm; like a waxwing?

Since I wrote that musing in 2010, I've been to Sulawesi and have seen and heard Hylocitrea (left). Its vocalizations do, indeed, recall waxwings.

Photos: Rob Hutchinson took the top two photo of the Hylocitrea Hylocitrea bonensis at Lore Lindu NP, Sulawesi, in September 2010. My photo was also in Lore Lindu NP, on 28 Sep 2011.

      Uncredited photos © Don Roberson. Credited photos © Rob Hutchinson/Birdtour Asia, as credited, and used with permission; all rights reserved.

Bibliographic note: There is obviously no "family book" and it is barely touched in HBW (no photo; Boles 2007).

Literature cited:

Boles, W.E. 2007. Family Pachycephalidae (Whistlers), pp. 374 –437 in Handbook of the Birds of the World (del Hoyo, J., A. Elliott & D.A. Christie, eds). Vol. 12. Lynx Edicions, Barcelona, Spain.

Coates, B.J., and K.D. Bishop. 1997. A Guide to the Birds of Wallacea: Sulawesi, the Moluccas and Lesser Sunda Islands, Indonesia. Dove Publ., Alderly, Australia.

Holmes, D. 1996. The Birds of Sulawesi. Oxford Univ. Press, Kuala Lumpur.

Norman, J.A., P.G.P. Ericson, K.A. Jønsson, J. Fjeldså, and L. Christidis. 2009. A multi-gene phylogeny reveals novel relationships for aberrant genera of Australo-Papuan core Corvoidea and polyphyly of the Pachycephalidae and Psophodidae (Aves: Passeriformes). Molec. Phylog. Evol. 52: 488-497.

Spellman, G.M., A. Cibois, R.G. Moyle, K. Winker, and F.K. Barker. 2008. Clarifying the systematics of an enigmatic avian lineage: what is a bombycillid? Molec. Phylog. Evol. 49: 1036-1040.