Time to finish one of those long-running series of Tet Zoo articles: at last, the long-awaited, much anticipated third and final instalment in the series on the clubs, spurs, spikes and claws present on the hands of numerous neornithine bird species. If you haven’t done so already, do check out the previous parts here (on hand claws in general, and carpal spurs and knobs in waterfowl) and here (on carpal spurs in charadriiforms).
Those previous instalments looked at claws (widely present in modern birds: far from unique to the Hoatzin Opisthocomus hoazin) and at keratin-sheathed bony knobs and spurs. All very neat I’m sure you’ll agree, but arguably less amazing than the structures I’m going to be discussing here: CLUBS. [Image above shows, at left, Pezophaps solitarius, by Frederick William Frohawk, and Xenicibis xympithecus, by Nick Longrich].
As we’ll see, birds of (at least) two very distinct neornithine lineages evolved bony clubs on their hands, and in both cases these seem to have been used in (probably intraspecific) combat.
The claws, spurs and other carpometacarpal structures discussed in these articles are, ordinarily, hardly ever mentioned in the literature. But the structures present in one recently extinct bird are, in contrast, mentioned just about every single time this species is discussed, and I’d even go as far as saying that their presence is “well known”. I’m of course referring to the Solitaire Pezophaps solitarius, a giant, recently extinct pigeon from Rodriguez (its anthropogenic extinction occurred some time between the 1730s and 1760s). Huge, rounded bony calluses – said by Newton & Newton (1868) to be “out of all proportion to anything of the kind yet known in ornithology” (p. 342) – are present on the proximal end of the male carpometacarpus, and appear to be hypertrophied extensor processes. These structures have a very rugose texture and would have been covered in life by horn [the adjacent diagram shown here is from Rand (1954); the annotated photo below was taken at the University of Museum of Zoology, Cambridge, UK].
The Huguenot refugee François Legaut, who famously observed these birds in life, described the presence of a rounded mass “as big as a musket ball” near the end of the wing. He even said that the birds whirred their wings in display, clapped them “like a rattle” against their sides, and used them in striking enemies. In many of the larger Solitaire specimens examined by Newton & Newton (1868), both the radius and ulna had fractured and healed in life, so it seems like a reasonable deduction to conclude that Solitaires fought with their wings, as do many other pigeons. A swelling is also present on the distal end of the Solitaire radius, so this region was likely covered in horn and/or calloused skin as well. These unusual features were unique to males so are assumed to have been used in male-male combat. Male Solitaires were substantially larger than females: with estimated masses of, respectively, 28 and 17 kg, a female would only be about 60% the mass of a large male (Livezey 1993). This is the largest reported case of sexual dimorphism in neognath birds (it’s exceeded by the dimorphism seen in moa, but they ain’t neognaths) [UPDATE: nope. Muscovy ducks, capercaillies and Great bustards all exhibit dimorphism that exceeds what's seen in the Solitaire. See comments. Another reminder not to believe everything you read, even when it does come from an authoritative source].
Pigeons in general fight by striking each other with their wings, so it seems that this behaviour was likely inherited from the Solitaire’s volant ancestors. In phylogenies, Pezophaps is close to Caloenas (Nicobar pigeons), Goura (crowned pigeons) and Didunculus (tooth-billed pigeons) (Shapiro et al. 2002). At least some of these living relatives of the Solitaire raise one or both of their wings when acting aggressively (Goodwin 1967). Here’s where things become more interesting…
There’s more than one large, terrestrial, knob-winged pigeon!
Having mentioned Didunculus, I’ve always been curious about the fact that some old sources (e.g., Rand 1954) refer to this pigeon – generally known as the Samoan tooth-billed pigeon* – as the Knob-winged pigeon. The idea that this close relative of dodos and solitaires might have enlarged bony knobs on its carpometacarpi is very interesting, but illustrations of its carpometacarpus (see the one shown below, from Worthy & Wragg (2008) [scale bar = 10 mm]) don’t show any unusual structures compared to other pigeons: the extensor processes in particular looks pretty average (certainly compared to that of Pezophaps). Livezey (1993, p. 275), however, noted in passing that the extensor processes of Didunculus are overlain by a cornified integument: yet another reminder (as if it were needed) that structures present in life aren’t always obvious from the underlying osteology.
* There’s only one living species (D. strigirostris) and it’s found on Samoa. Fossils show that it once lived on Fiji, and an extinct species (D. placopedetes) is known from Tonga. Didunculus is thus a ‘pseudo-endemic’ of Samoa (Steadman 2006).
Things get better when we look at other members of this ‘Caloenas group’ of pigeons, however. Both Goura (the crowned pigeons) and the recent extinct Fijian form Natunaornis gigoura (the Viti Levu giant pigeon, sometimes jokingly referred to the Fijian dodo) have inflated, bulbous extensor processes, with those of Natunaornis being especially big (Worthy 2001). In fact, I’d go so far as to say that the inflated extensor processes of Goura and Natunaornis look like ‘prototype’ versions of the enormous ones present in Pezophaps. This wasn’t lost on Trevor Worthy, who wrote that “A similar development of the metacarpal process in Didunculus (Livezey 1993) and in Goura (data herein) is suggestive that these taxa shared with Natunaornis the use of their wings in combative behaviour” (p. 780). [There are very few life restorations of Natunaornis. The one on the stamp, shown below, errs in making the bird's bill too gracile: it seems that it was actually deep and robust, as shown in my speculative picture shown at left. This reconstruction has been used on Tet Zoo before]. Incidentally, there’s no evidence that the Dodo Raphus cucullatus had wing knobs or clubs, though the suggestion has been made (by Richard Owen) that the wings were used in fighting.
A few other birds not mentioned here or in the previous articles might also have cornified knobs on their hands. Rand (1954) mentioned such structures in Megapodius megapodes and some thrushes, but I’ve been unable to find more information and haven’t (yet) read any more about these possible occurrences (on the thrushes… I don’t suppose it’s possible that someone confused the flightless pigeon called the Solitaire with the American thrushes – Cichlopsis, Entomodestes and Myadestes – called solitaires?). Andrews (1901) made the interesting suggestion that roughened areas on the extensor process of Phorusrhacos indicated the presence of a spur or horny knob on this part of the hand. That’s entirely plausible, though note that it’s nothing to do with those suggestions of giant hand claws previously mooted for some phorusrhacids.
Note that the knobs that we’re talking about here are quite similar to the previously discussed knobs present on steamer ducks and some other waterfowl.
Ninja ibis from Jamaica
We finish it all by looking at another extinct bird that also possessed distinctive wing armament: I’m referring to the flightless ibis Xenicibis xympithecus from Jamaica, sometimes called the Club-winged ibis. I started writing the article you’re reading now in July 2010 and had no idea at all that a paper describing the club-winged condition of Xenicibis in definitive fashion was in the works (though I was familiar with this research, having heard about it all off Nick Longrich some years ago). Yes, as you’ll likely now know, Nick Longrich and Storrs Olson published their description and interpretation of this remarkable bird’s wings in January of this year (to date, only the online version is out). The paper (Longrich & Olson 2011) got a lot of press coverage. I was even asked to do a radio interview on it (after all, I did play a crucial role in the research [massive joke]). It was pretty weird as the radio host asked me to describe what kind of ‘dino’ Xenicibis was. I proceeded to explain what ibises were and how they were actually pretty familiar birds. Anyway…
Xenicibis and its incredible flail-like wings have in fact gotten so much coverage online (in the blogosphere and elsewhere (honourable mention of Ed Yong)) that there isn’t much I can say that you won’t already have heard before. The carpometacarpus is massive, long, curved and equipped with thick bone walls. The radius is unusually robust compared to that of most birds, while the wrist and elbow were fully mobile.
The weird wing bones of this bird have resulted in previous suggestions that it was possibly quadrupedal and that it used its hands as props, like crutches (I used to have a cartoon depicting this idea but can’t find it anymore. UPDATE: FOUND IT!). I’ve also heard informal (and very much unpublished) suggestions that these clubs were used for bashing snakes. As Longrich & Olson (2011) argue, the wing structure seen in Xenicibis indicates that it used these limbs as flail-like combative organs, probably against other members of its own species. However, because it lived alongside various snakes, raptors and other predators it’s certainly plausible that these bizarre wings were also used to fight off or even kill such animals. And good evidence for use of the wings in combat comes from healed fractures in the upper arm and hand.
Many people who regularly get close to, or handle, birds know that (as we’ve discussed on Tet Zoo quite a bit before) they’re frequently pretty formidable animals for their size. Angry waterfowl, chickens, raptors and gulls can be real nasty: powerful and gutsy enough to fight off and injure (even kill) mammals bigger than they are. Should you encounter a specialised, weapon-bearing bird of any sort (either here or in the past, should you go time travelling) my advice is to be very, very careful and to try not to piss it off. Should you be attacked, be sure that someone is taking photos – – – that kind of stuff is blogging gold!!!
For previous articles on manual weaponry in birds, and on avian hands in general, see…
- Raven, the claw-handed bird, last of the phorusrhacids
- Attack of the flying steamer ducks
- Yes, it was a kiwi
- Dissecting an emu
- Dissecting Ozbert the ostrich
- Detachable wing-daggers. Amazing waterfowl facts part III
- Clubs, spurs, spikes and claws on the hands of birds (part I)
- Spurs and blades on the wings of jacanas, lapwings, sheathbills and archaeotrogonids (clubs, spurs, spikes and claws part II)
And for more on pigeons, big or otherwise, see…
PS – YES… at last, this short series is complete. Now to do like it says here, and kill the others too…
Refs – –
Andrews, C. W. 1901. On the extinct birds of Patagonia-I: The skull and skeleton of Phororhacos inflatus Ameghino. Transactions of the Zoological Society of London 15, 55-86.
Goodwin, D. 1967. Pigeons and Doves of the World. British Museum (Natural History) (London).
Livezey, B. C. 1993. An ecomorphological review of the dodo (Raphus cucullatus) and solitaire (Pezophaps solitaria), flightless Columbiformes of the Mascarene Islands. Journal of Zoology 230, 247-292.
Longrich NR, & Olson SL (2011). The bizarre wing of the Jamaican flightless ibis Xenicibis xympithecus: a unique vertebrate adaptation. Proceedings. Biological sciences / The Royal Society PMID: 21208965
Newton, A. & Newton, E. 1868. On the osteology of the Solitaire or Didine bird of the Island of Rodriguez. Proceedings of the Royal Society 103, 428-433.
Rand, A. L. 1954. On the spurs on birds’ wings. The Wilson Bulletin 66, 127-134.
Shapiro, B., Sibthorpe, D., Rambaut, A., Austin, J., Wragg, G. M., Bininda-Emonds, O. R. P., Lee, P. L. M. & Cooper, A. 2002. Flight of the dodo. Science 295, 1683.
Steadman, D. W. 2006. An extinct species of tooth-billed pigeon (Didunculus) from the Kingdom of Tonga, and the concept of endemism in insular landbirds. Journal of Zoology 268, 233-241.
Worthy, T. H. 2001. A giant flightless pigeon gen. et sp. nov. and a new species of Ducula (Aves: Columbidae), from Quaternary deposits in Fiji. Journal of The Royal Society of New Zealand 31, 763-794.
– . & Wragg, G. M. 2008. A new genus and species of pigeon (Aves: Columbidae) from Henderson Island, Pitcairn Group. Terra Australis 29, 419-510.