More than Four and Twenty Blackbirds

The Tristan thrush or Starchy, Turdus eremita, an endemic bird of the remote Tristan da Cunha group of islands in the South Atlantic, scavenging on a dead penguin (starchies have decidedly more catholic tastes than other thrushes). Photo by Lex.

Turdus, the thrushes, is a large cosmopolitan genus of birds found throughout the world except for Australia. The extent of the genus' circumscription has varied between authorities, though most recent authors exclude the ground-thrushes of the genus Zoothera. Conversely, phylogenetic studies have indicated that the previously monotypic genera Cichlherminia lherminieri of the Caribbean and Nesocichla eremita from Tristan da Cunha should be subsumed within Turdus (Voelker et al., 2007). At present, it seems unlikely that Turdus will be further subdivided; as the basalmost species in the genus is likely to be the mistle thrush Turdus viscivorus, which happens to also be the type of the genus, any subdivision would require that Turdus be reduced to a single species and all other species placed in new genera.


The blackbird Turdus merula, a species found throughout northern Eurasia (and introduced to New Zealand). Only the males are black; the females are dark mottled brown and have grey rather than yellow beaks. Photo by Bence Mate.

Of the 60+ species remaining in Turdus, many are widespread and divided into a number of subspecies that may or may not be promoted to separate species by future researchers. As an extreme example, a study on variation between geographically separated populations of the island thrush Turdus poliocephalus, whose distribution extends from Sumatra and the Philippines east to Norfolk Island* and Vanuatu, suggested that there may be grounds for dividing them between nearly forty diagnostic taxonomic units (Peterson, 2007).

*At least, it did. The Tasman Sea populations of T. poliocephalus have, unfortunately, since shuffled off this mortal coil.


The St Lucia forest thrush, Turdus lherminieri sanctaeluciae. Like T. eremita, this is a distinctive species that was previously placed in its own genus. Photo by Jean-Michel Fenerole.

The base coloration of most species of Turdus can be described as 'mottled brown', though notable exceptions (at least as males) include the grey and red American robin T. migratorius and the blackbird T. merula. Most members of the genus are more highly regarded for their voices rather than their looks, an attribute honoured in both the vernacular and scientific names of the song thrush Turdus philomelos* ("lover of song"). As with other speciose songbird clades, variation in song has turned out to be significant in separating closely related species. Both the Príncipe thrush T. xanthorhynchus (Melo et al., 2010) and the black-throated thrush T. atrogularis (Sangster et al., 2009) differ in their songs (among other things) from species with which they were previously considered conspecific.

*Older references may one of the names Turdus musicus or Turdus ericetorum for this species. Both these names have since been suppressed by the ICZN. The history of Turdus musicus is particularly turgid, as authorities had disagreed over whether the name should be applied to the song thrush or to the redwing (now Turdus iliacus) (Mayr & Vaurie, 1957). Both T. musicus and T. iliacus appeared in Linnaeus' 1758 Systema Naturae. Unfortunately (whether because he was unclear on the distinction between the species, or by a simple composition error), Linnaeus confused the two species' descriptions: under T. musicus, he gave a description of the redwing but provided sources referring to the song thrush, while the entry for T. iliacus attached a description of the song thrush to references referring to the redwing! (The significance of Linnaeus' sources to his descriptions has previously been discussed in the sperm whale nomenclature post.) Mayr & Vaurie's (1957) application buried the name Turdus musicus and designated a neotype to fix Turdus iliacus firmly to the redwing.

REFERENCES

Mayr, E., & C. Vaurie. 1957. Proposed use of the plenary powers to suppress the specific name "musicus" Linnaeus, 1758, as published in the combination "Turdus musicus" and to approve a neotype for "Turdus iliacus" Linnaeus, 1758, the Eurasian redwing (class Aves). Bulletin of Zoological Nomenclature 13 (6): 177-181.

Melo, M., R. C. K. Bowie, G. Voelker, M. Dallimer, N. J. Collar & P. J. Jones. 2010. Multiple lines of evidence support the recognition of a very rare bird species: the Príncipe thrush. Journal of Zoology 282 (2): 120-129.

Peterson, A. T. 2007. Geographic variation in size and coloration in the Turdus poliocephalus complex: a first review of species limits. Scientific Papers, Natural History Museum, The University of Kansas 40: 1-17.

Sangster, G., A. B. van den Berg, A. J. van Loon & C. S. Roselaar. 2009. Dutch avifaunal list: taxonomic changes in 2004–2008. Ardea 97 (3): 373–381.

Voelker, G., S. Rohwer, R. C. K. Bowie & D. C. Outlaw. 2007. Molecular systematics of a speciose, cosmopolitan songbird genus: defining the limits of, and relationships among, the Turdus thrushes. Molecular Phylogenetics and Evolution 42: 422-434.

The Tomb of the Unknown Honeyeater

Some of the birds referred to in this post. Clockwise from top left - Bombycilla garrulus, the Bohemian waxwing, Bombycillidae; Chaetoptila angustipluma, a Hawaiian honeyeater; two true honeyeaters (Meliphagidae), Anthochaera carunculata (red wattlebird) and Prosthemadera novaeseelandiae (tui); and Moho nobilis, the Hawai'i 'o'o, a Hawaiian honeyeater. Painting by John Anderton.

Fleischer, R. C., H. F. James & S. L. Olson. 2008. Convergent evolution of Hawaiian and Australo-Papuan honeyeaters from distant songbird ancestors. Current Biology 18: 1-5.

GrrlScientist brought my attention yesterday to an interesting new publication on the phylogeny of the Hawaiian honeyeaters. Not, I hasten to explain, the Hawaiian honeycreepers, the Drepanidini clade of birds unique to Hawaii that has become famed for their remarkable adaptive radiation into a whole range of ecological niches, but a smaller clade of five species, Chaetoptila angustipluma and the four species of 'o'o (Moho), that is also unique to Hawaii.

The honeyeaters of the family Meliphagidae are a sizable, fairly heterogenous assemblage of songbirds (Oscines) that are found throughout the Australo-Papuan region, with outliers on various Pacific islands such as New Zealand and Samoa. Despite including a diversity of morphologies, meliphagids are well established as a family, united by features such as a brushed tongue used for taking nectar from flowers (hence, of course, the name "honeyeaters"). The five Hawaiian species share many of these features, and are fairly similar in appearance to Australasian meliphagids, so have always been regarded as meliphagids themselves. The study being discussed here found in a DNA phylogenetic analysis that this was not the case.

Conducting a molecular analysis of Hawaiian honeyeaters is a remarkable achievement in itself because, tragically, not one of the five species remains alive today. All became extinct in the last two centuries. The last surviving species was the smallest, the Kauai 'o'o (Moho braccatus), the last male of which was sighted in 1987 (just to turn the pathos up a notch, a short video of this last individual can be seen here). The Hawaiian honeyeaters therefore join an all-too-long list of birds extinct on the Hawaiian islands since human colonisation, such as the moa-nalo. In the absence of living specimens, Fleischer et al. had to extract DNA from museum specimens, but were able to do so for all five species.

Phylogenetic analysis of these samples showed that, as mentioned above, Chaetoptila and Moho were not related to the true meliphagids. As I've explained elsewhere, recent molecular analyses have consistently identified three large clades within the songbirds (as well as a smattering of smaller clades), the Meliphagoidea (including the meliphagids), Corvoidea and Passerida (including most Northern Hemisphere songbirds). The Hawaiian honeyeaters are not members of the Meliphagoidea, but instead belong to an entirely different clade, the Passerida. Within the Passerida, they belong to an assemblage that includes the Holarctic waxwings (Bombycilla), North American silky flycatchers (Ptilogonatinae) and Caribbean palmchat (Dulus dominicus). Most authors have united these birds in the family Bombycillidae, and the name was recently used in this sense by Spellman et al. (2008). While Fleischer et al. (2008) establish a new family Mohoidae for the Hawaiian honeyeaters, that clade would belong within Bombycillidae in the broad sense. Relationships of the Bombycillidae within the Passerida remain largely unresolved.

The Hawaiian honeyeaters have not been the first birds to abscond from the Meliphagidae in recent years. I have previously discussed the discovery that the New Zealand stitchbird (Notiomystis cincta) is related to the New Zealand wattlebirds, and perhaps a basal member of the Corvoidea. The South African sugarbirds of the genus Promerops, long unsettled as meliphagids, belong to the Passerida and are basal members of the Passeroidea assemblage that includes finches and sparrows (Beresford et al., 2005). The Bonin honeyeater (Apalopteron familiare) is also a member of the Passerida, and falls within the family of white-eyes, Zosteropidae (Driskell & Christidis, 2004) - which I wasn't too surprised to hear because, if you ignore the "meliphagid" brushed tongue, Apalopteron really does look like a big white-eye. Still, the Hawaiian honeyeaters are probably the most typically "meliphagid-like" birds to be recognised as non-meliphagids.

In another interesting recurring theme in oscine phylogeny, the reclassification of Hawaiian honeyeaters, while morphologically unexpected, makes a certain degree of biogeographic sense. Most colonisation of the Hawaiian islands seems to have been derived from North America rather than the western part of the Pacific, with Hawaiian honeycreepers, warblers, geese and violets, among others, all having demonstrated North American (and often northern North American) affinities. As pointed out by a commentator at GrrlScientist's post linked to above, the only Hawaiian bird that still possesses western Pacific affinities is the monarch flycatcher Chasiempis sandwichensis, whose Monarchidae affinities were supported by Filardi & Moyle (2005).

That Hawaiian honeyeaters are such a distinct lineage makes their loss all the more tragic. An extra dose of tragedy that verges on the comic surrounds the most distinct of the mohoids, Chaetoptila angustipluma. Those of my readers who have heard of it before may have noticed that I have deliberately avoided using the vernacular name given to this bird, the kioea. My reason for doing so is that there is reason to doubt whether this name properly belongs to Chaetoptila at all. "Kioea" is actually the Hawaiian name for the bristle-thighed curlew (Numenius tahitiensis), a migratory wading bird and not very much like a honeyeater at all. References to "kioea" as a seabird include the Kumulipo, the epic poem that recited the genealogy of the Hawaiian royal family:

Hanau ke Kioea ka makua,
Puka kana keiki he Kukuluae'o, lele.

The Kioea was born and became parent,
Its offspring was a Kukuluaeo [stilt, Himantopus knudseni], and flew.

--Hawaiian text from here, 1897 translation by Queen Liliuokalani.

Peale (1848) provided no common name for Chaetoptila angustipluma when he first described it (as Entomiza angustipluma - Entomyza is a meliphagid genus). Bryan & Greenway (1944) gave the name "kioea" for this species, but with a question mark, and they also used the name elsewhere for the curlew - I haven't been able to find whether this is the first recorded association between the name and Chaetoptila. Not only has Chaetoptila been cruelly forced out of existence, but it has potentially been subjected to the indignity of a name that is not its own. It truly is the unknown honeyeater.

REFERENCES

Beresford, P., F. K. Barker, P. G. Ryan & T. M. Crowe. 2005. African endemics span the tree of songbirds (Passeri): molecular systematics of several evolutionary ‘enigmas’. Proceedings of the Royal Society of London Series B – Biological Sciences 272: 849-858.

Bryan, E. H., Jr & J. C. Greenway Jr. 1944. Check-list of the birds of the Hawaiian islands. Bulletin of the Museum of Comparative Zoology 94 (2): 92-140.

Driskell, A. C., & L. Christidis. 2004. Phylogeny and evolution of the Australo-Papuan honeyeaters (Passeriformes, Meliphagidae). Molecular Phylogenetics and Evolution 31 (3): 943-960.

Filardi, C. E., & R. G. Moyle. 2005. Single origin of a pan-Pacific bird group and upstream colonization of Australasia. Nature 438 (7065): 216-219.

Peale, T. R. 1848. Mammalia and Ornithology. C. Sherman: Philadelphia.

Spellman, G. M., A. Cibois, R. G. Moyle, K. Winker & F. K. Barker. 2008. Clarifying the systematics of an enigmatic avian lineage: what is a bombycillid?. Molecular Phylogenetics and Evolution 49 (3): 1036-1040.