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.