Coscoroba

So what was the bird in Wednesday's photo? It didn't take long for it to be recognised for what it was, a coscoroba.

The coscoroba Coscoroba coscoroba, photographed by Christopher Valentine at the Jardin des Plantes, Paris. Photographing this animal was not entirely easy: it was in the process of preening, and every time that we tried to get a photo, its head would dive back into its feathers and we'd have yet another photo of a headless coscoroba.

The coscoroba (its name refers to the sound of its call) is a waterbird of coastward parts of southern South America, with its range having extended over the past century as far north as Uruguay (Kear 2005). In general appearance, it resembles a small swan (and is often called the 'coscoroba swan'). The most obvious difference between a swan and a coscoroba is that the latter lacks a bare patch of skin between its eyes and its beak. Coscorobas also have a flatter, more 'duck-like' beak than swans. Another significant difference can be seen in their behaviour: swans and geese are characterised by what is called a 'triumph ceremony', where a male approaches his partner (swans form life-long pair bonds), raising and lowering his head while calling, and is answered by her in kind. This behaviour is particularly common after the male has seen off a potential rival (hence the name), and probably serves to maintain the pair bond. Coscorobas, it seems, are far too refined for such brazen posturing, and limit themselves to a little quiet murmuring of their eponymous call (Johnsgard 1965).

Because of its 'not-quite-swannish' nature, the coscoroba has often been seen as a link between swans and some other group of waterfowl, such as geese or whistling ducks. Molecular studies (e.g. Donne-Goussé et al. 2002) have placed it as sister to the Cape Barren goose Cereopsis novaehollandiae of Australia, with the two together sister to the swans. This does seem a little counter-intuitive, as superficially Cereopsis does not appear very coscoroba-like, but it is relatively well-supported. The purported similarities between the coscoroba and whistling ducks, on the other hand, are quite possibly plesiomorphies retained from the ancestral waterfowl.

The Cape Barren goose Cereopsis novaehollandiae, potential sister to the coscoroba. Photographed by Norm Hanson.

REFERENCES

Donne-Goussé, C., V. Laudet & C. Hänni. 2002. A molecular phylogeny of Anseriformes based on mitochondrial DNA analysis. Molecular Phylogenetics and Evolution 23: 339-356.

Johnsgard, P. 1965. Handbook of Waterfowl Behavior. University of Nebraska: Lincoln.

Kear, J. 2005. Ducks, Geese and Swans. Oxford University Press.

A Pathetic Plea for Recognition, and a Platypus-billed Duck

The closing date of submissions for this year's OpenLab, an annual collection of the year's best science-blog writting (as judged by the judges), is the 1st of December - a week from today. If there has been anything here at Catalogue of Organisms over the past year (since December the 1st last year), please (please!) submit it for consideration. Please! Go through the archive in the right sidebar, pick out your favourites, and make your contribution towards restoring my fragile sense of self-worth.

Otherwise, your humble host is still fairly knackered after getting back from the field yesterday (two weeks away = nearly three hundred e-mails [mostly spam], 1000+ entries on Google Reader, one pair crossed eyes). So just a brief finishing note:



This is the braincase of Talpanas lippa, a subfossil duck species, about the size of a mallard, described from Kauai by Iwaniuk et al. (2009) in Zootaxa today (and the article is freely available to all comers). As well as the braincase, Talpanas is also represented by pieces of jaw and leg bones and a partial pelvis. The name means "nearly blind mole-duck" - Talpanas would have had small, piggy little eyes, quite unusual in a bird, and would have almost certainly been nocturnal and flightless (flying blind is not usually recommended). Though the complete beak is still unknown, the available jaw pieces indicate that it would have been very broad. The leg bones indicate that Talpanas was a walker rather than a swimmer, so Talpanas was probably a forager for small invertebrates among forest litter; this is the lifestyle currently pursued by the kiwi, another nocturnal bird with relatively small eyes. Iwaniuk et al. suggest that Talpanas also resembled a platypus in using its broad bill to feel for invertebrates amongst the soil. The opening for the trigeminal nerve in the braincase is very large like that of a platypus (it's the opening labelled 'V' on the images above - take a look, it's freaking huge), indicating that Talpanas' bill would have been very sensitive to touch. Unfortunately, the skull of Talpanas is so unusual that its relationships with other anseriforms are obscure.

The Hawaiian Superducks

The turtle-jawed moa-nalo, Chelychelynechen quassus, largest of this group of birds. Image by Stanton Fink.

The always impressive Darren Naish put up a post a couple of days ago on recent publications about phorusrhacoids, the giant carnivorous birds that once stalked South America (and only a gigantic carnivorous bird can truly be said to "stalk"), including (among other things) the recent claim that one supposed phorusrhacoid, Brontornis, was not a phorusrhacoid at all but a relative of the Anseriformes. In the course of the comment thread on that post, mention has been made of the moa-nalo, and I thought I'd put up an explanatory post for anyone not familiar with the latter.

Moa-nalo were large (up to 7.6 kg - Ziegler, 2002), flightless goose-like birds that were once found in the Hawaiian Islands, but seem to have not long survived the arrival of hungry humans. To date, four species have been described from various islands (Olson & James, 1991) - Chelychelynechen quassus from Kauai*, Thambetochen xanion from Oahu, T. chauliodous from lowland Maui and Molokai, and Ptaiochen pau from highland Maui. Moa-nalo are not yet known from the main island of Hawaii, which was home to two species of Branta goose (Paxinos et al., 2002), including the (just) surviving nene (B. sandvicensis). Branta geese were also found on the other Hawaiian islands. Wetmore (1943) described a fossil anserid species from Hawaii, Geochen rhuax, that he regarded as distinct from Branta (and very like the Australian Cereopsis), but the fragmentary remains this species was described from are not really sufficient to tell whether it is a goose or moa-nalo (or something else again)**. The unnamed 'giant Hawaiian goose' of Olson & James (1991) is quite definitely a Branta (Paxinos et al., 2002).

*Wryly amusing quote of the day comes from the etymology of the species name for this taxon (Olson & James, 1991): "Latin, quassus , broken, shattered, in reference to the regrettably fragmented condition of the type material, which was probably deposited as a complete skeleton but was unfortunately exposed in a jeep trail."

**Olson & James (1991) again, referring to the discovery of the Geochen material underneath an old lava flow: "From their very friable and warped appearance, the bones were almost certainly heated until glowing, with all organic material in the bone having been combusted."

Perhaps most interesting about the moa-nalo is their phylogenetic relationships (isn't it always?). Despite their goose-like appearance, Olson & James (1991) suggested on the basis of their ossified syringeal bullae that moa-nalo were actually more closely related to the dabbling ducks of the genus Anas (two species of which are also found on Hawaii), and possibly even derived from the common mallard (A. platyrhynchos). This view was corroborated to some extent by ancient DNA analysis (Sorenson et al., 1999) which, while it found the moa-nalo as the sister group to Anas rather than within it, definitely indicated a duck rather than goose ancestry for them. The moa-nalo therefore seem to have undergone a rapid and significant change in morphology as they adapted to flightless herbivory. The Molokai population of Thambetochen chauliodous seems to have actually gone so far as to lose the furcula!

REFERENCES

Olson, S. L., & H. F. James. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: part I. Non-Passeriformes. Ornithological Monographs 45: 1-88.

Paxinos, E. E., H. F. James, S. L. Olson, M. D. Sorenson, J. Jackson & R. C. Fleischer. 2002. mtDNA from fossils reveals a radiation of Hawaiian geese recently derived from the Canada goose (Branta canadensis). Proceedings of the National Academy of Sciences of the USA 99: 1399-1404.

Sorenson, M. D., A. Cooper, E. E. Paxinos, T. W. Quinn, H. F. James, S. L. Olson & R. C. Fleischer. 1999. Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society of London Series B – Biological Sciences 266: 2187-2193.

Wetmore, A. 1943. An extinct goose from the island of Hawaii. Condor 45 (4): 146-148.

Ziegler, A. C. 2002. Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press.