I like ducks, and I particularly like steamer ducks. Again, here we revisit some Tet Zoo ver 1 text that was originally published in 2006 as part of the Ten Birds Meme.
The most widely distributed of the four Tachyeres species*, the Flying steamer duck T. patachonicus inhabits both the fresh and marine waters of the Falklands and southern Patagonia and Tierra del Fuego. While all other steamer-ducks are flightless, T. patachonicus is (obviously) not, and in contrast to its flightless relatives it has proportionally bigger pectoral muscles and lower wing loadings. But what makes the species especially interesting is that some males within the species actually have wing loadings that are too high to permit flight, and are thus flightless (Humphrey & Livezey 1982, Livezey & Humphrey 1986). So, within a single species, there are both flighted and flightless individuals. It is almost as if the species is poised in the transition to full flightlessness, and indeed both morphological and genetic studies (Corbin et al. 1988) agree that T. patachonicus is the most basal member of its otherwise flightless genus. Flighted and flightless individuals are known to have also occurred in some recently extinct anseriform species, incidentally.
* One species, T. leucocephalus, was only described in 1981.
But there’s more. Steamer-ducks are notoriously pugnacious. Heavy-bodied and robust compared to other ducks, they have tough skin, a massive head and neck, and are equipped with keratanised orange knobs on the proximal parts of their carpometacarpi. Both sexes use these wing knobs in territorial fights and displays. Fighting males grab each other by the head or neck and then whack each other vigorously with the wing knobs, and fights can last for up to 20 minutes. Both birds sometimes submerge during the fight, and come up still fighting. This reminds me of scenes in films where super-heroes and villains (e.g., Spider-man vs Doc Oc) fall off buildings together and continue to battle even while plummeting toward the ground, but that’s just me. An aggressive steamer-duck approaches an ‘enemy’ by either adopting the so-called submerged sneak posture (only the top of the head and back and tail tip are visible), or by ‘steaming’ noisily across the surface (the ducks charge at speed, throwing their wings like the paddles of a paddle-steamer, hence the vernacular name).
Here’s where things get especially cool. Other waterbirds are shit-scared of steamer-ducks, and ‘mass spooks’ of other duck species, grebes and coots have been recorded when these birds saw or heard the local T. patachonicus. You see, they attack and kill other waterfowl. A particularly detailed steamer-duck attack on a Shoveler Anas platalea was recorded by Nuechterlein & Storer (1985a), and I here summarise the account they describe on p. 89.
A male steamer-duck caught a male shoveler by the neck and began pounding it with its wing knobs [adjacent photo from Arthur Grosset’s Birds]. The female steamer-duck displayed excitedly nearby. The shoveler was held beneath the water, then yanked up and beat some more. The male steamer-duck took a break and displayed with his female, then he went back to the shoveler, grabbed it again by the neck and proceeded to beat it another 15-20 times. By now the shoveler was looking pretty limp (though still alive). It was pecked at and released and both steamer-ducks displayed together again, and the male steamer-duck now began to move away from the shoveler. The shoveler now began to move (slowly) toward the shore and eventually got there. Then it died. ‘Examination of the specimen disclosed several broken bones, hemorrhages in the lower neck region and massive internal bleeding at the base of the right leg’ (p. 89). During the course of their study at Laguna de la Nevada, Santa Cruz Province, Argentina, Nuechterlein & Storer (1985a) picked up the carcasses of six ducks that had definitely been killed by steamer-ducks within a single week. Why steamer-ducks are so aggressive remains the source of debate (Murray 1985, Livezey & Humphrey 1985a, b, Nuechterlein & Storer 1985b). But don’t mess with them.
Refs – –
Corbin, K. W., Livezey, B. C. & Humphrey, P. S. 1988. Genetic differentiation among steamer-ducks (Anatidae: Tachyeres): an electrophoretic analysis. The Condor 90, 773-781.
Humphrey, P. S. & Livezey, B. C. 1982. Flightlessness in flying steamer-ducks. The Auk 99, 368-372.
Livezey, B. C. & Humphrey, P. S. 1985a. Territoriality and interspecific aggression in steamer-ducks. The Condor 87, 154-157.
– . & Humphrey, P. S. 1985b. Interspecific aggression in steamer-ducks. The Condor 87, 567-568.
– . & Humphrey, P. S. 1986. Flightlessness in steamer-ducks (Anatidae: Tachyeres): its morphological bases and probable evolution. Evolution 40, 540-558.
Murray, B. G. 1985. Interspecific aggression in steamer-ducks. The Condor 87, 567.
Nuechterlein, G. L. & Storer, R. W. 1985a. Aggressive behavior and interspecific killing by Flying steamer-ducks in Argentina. The Condor 87, 87-91.
– . & Storer, R. W. 1985b. Interspecific aggression in steamer-ducks. The Condor 87, 568.