Pseudopodoces, the corvid that wasn't

More from the archives - and again this is from the Ten Bird Meme of 2006.


If convergence is one of the most interesting evolutionary phenomena, then the Ground tit Pseudopodoces humilis should become a text-book example of it, on par with thylacines vs wolves and ichthyosaurs vs dolphins [adjacent photo from here]. Described in 1871 by A. Hume, the Ground tit is a weak-flying brown passerine of the Tibetan plateau, often superficially likened to a wheatear. But for most of the time that we've known of it, it has not gone by the name Ground tit at all: rather, it has been termed Hume's ground-jay (or Little ground-jay or Tibetan ground-jay or Hume's ground-pecker). This is because, you see, it was always regarded as a ground-jay, that is, as a terrestrial corvid. While superficially similar to true ground-jays (the four Podoces species), it was always regarded as a highly aberrant member of Corvidae, and as the smallest member of the group. Hume in fact initially described P. humilis as a member of Podoces. Like Podoces, P. humilis possesses a slender, decurved bill, pale brown plumage and a dry, open-country habitat. However, they're also highly different. While ground-jays run, P. humilis hops, and while ground-jays use stick nests, P. humilis nests in tunnels or burrows. Ground-jays are also much larger than P. humilis and exhibit white wing patches and dark, iridescent plumage patches. In recognition of these differences, P. humilis was given its own subgenus within Podoces in 1902, and in 1928 this was elevated to generic status.

But the allocation of P. humilis to Corvidae wasn't really doubted until prominent osteological differences between P. humilis and ground-jays were noted by Borecky (1978). Borecky doubted the classification of P. humilis as a corvid and hinted at an affinity with starlings. In her 1989 phd study on corvid phylogeny, Sylvia Hope agreed that P. humilis was utterly unlike corvids, and most like nuthatches and tits. Despite these objections, P. humilis has remained classified as a corvid in most standard works on Corvidae (Goodwin 1986, Madge & Burn 1999) and indeed in most general works on birds. To resolve the issue once and for all, Helen James and colleagues performed a detailed analysis of the morphology and genetics of P. humilis, comparing it widely with other passerines (James et al. 2003). All the data showed, pretty conclusively, that P. humilis is not a corvid, but in fact a parid. A tit. A unique, highly novel tit to be sure, but a tit nonetheless, hence the new vernacular name. Incidentally, the paintings in James et al. (2003) were produced by my good friend Julian Hume. His office is next door to mine [UPDATE: well, it was in 2006. Not any more].

Refs - -

Borecky, S. R. 1978. Evidence for the removal of Pseupodoces humilis from the Corvidae. Bulletin of the British Ornithologists's Club 98, 36-37.

Goodwin, D. 1986. Crows of the World. Trustees of the British Museum (Natural History), London.

James, H. F., Ericson, P. G. P., Slikas, B., Lei, F.-M., Gill, F. B. & Olson, S. L. 2003. Pseudopodoces humilis, a misclassified terrestrial tit (Paridae) of the Tibetan Plateau: evolutionary consequences of shifting adaptive zones. Ibis 145, 185-202.

Madge, S. & Burn, H. 1999. Crows & Jays. Christopher Helm, London.

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Interesting, this is sort of a hint that aberrant members of any lineage might warrant a revision. I remember hearing from a friend that passerines are characterized by hopping when they are on ground. I have no idea if that is true or not, but if so, it should have given hints on the true affinities of this bird.


I remember hearing from a friend that passerines are characterized by hopping when they are on ground.

It's true that most passerines, including parids and small corvids, mostly hop on the ground. But others (e.g., lyrebirds, larks, pipits, wagtails, and starlings) walk. And yet others (e.g., large corvids) do both, depending on the situation. There are also some non-passerines (e.g., woodpeckers) that hop on the ground.

But Pseudopodoces betrays its tit affinity by its choice of nesting place:

while ground-jays use stick nests, P. humilis nests in tunnels or burrows.

Parids typically nest in tree cavities (or nestboxes), while corvids* don't. In the treeless semi-desert it lives in, Pseudopodoces has just switched to the next best thing.

* The jackdaws Corvus monedula and C. dauuricus nest in tree cavities, however.

That is really cool. (Convergent evolution is always interesting).

By William Miller (not verified) on 10 Dec 2008 #permalink

I had no idea tits could look like this.

Cool birds, and very common once you get to (relatively) remote upland steppes of Quinghai, Tibet or Ladakh.

Their ability to jump is amazing - they hop like little kangaroos, even several times own height up the slope.

Also, little Pseudopodoces is my favorite argument against cladistics. The genus Parus is perfectly good group biologicaly and morphologicaly, but to accomodate Pseudopodoces it was broken up into several near identical ones. So Coal Tit is Periparus, Bluetit is Cyanistes and Marsh Tit is Poecile.

I was amused to learn that, in order to avoid sniggering in zoology classrooms, tits were renamed chickadees in the United States. When you've grown up thinking of tits as birds too it seems perfectly normal!

By Roger Close (not verified) on 10 Dec 2008 #permalink

Hey, if you think this post's subject matter is funny, just wait until Darren writes about phalacrocoracids. Then he'll be talking about 'shags'.

Also, little Pseudopodoces is my favorite argument against cladistics.

You are confusing cladistics (the method to reconstruct phylogenetic trees) with nomenclature.

Also, your argument is wrong. What you are really against is the fact that the ICZN doesn't allow anything except subgenus and "group of species" between the ranks of genus and species; if that weren't the case, Parus could stay a genus.

And then, under phylogenetic nomenclature, this problem evaporates: you can have Cyanistes inside Parus in phylogenetic nomenclature. :-|

By David Marjanović (not verified) on 11 Dec 2008 #permalink

Pseudopodoces betrays its tit affinity...

I won't tell you how I betray mine...