EPOW - Ecology Picture of the Week

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Flighted and Flightless

Credit & Copyright:  Dr. Bruce G. Marcot
  

Explanation:  Last week, we explored how two seemingly different lizards are actually of the same species.  This week, here are two ducks that look the same but are of different species.  And boy, are they different.   Here are two of four recognized species of steamer-ducks, so named because when they swim they often use their wings in a forceful paddling motion like a steamer boat.   In the pair of photos above, the duck on the left flies whereas the duck on the right is flightless and sports only stubby wings.   Although the wings of the Flightless Steamer-duck are much reduced, as are the wing bones (especially the ulna, radius, and caropometacarpus), this duck still has very strong pectoral muscles and the breast "keel" bone because of its "steaming" means of locomotion in the water when using its wings as paddles.      A pair of Flying Steamer-ducks in the Gulf of Ancud between Chiloe Island and the mainland, along south coastal Chile. A solitary Flightless Steamer-duck in coastal waters along sea stacks near a penguin colony along west coast Chiloe Island, southern Chile.    Flightless Steamer-ducks are larger in size (length 83 cm or 33 inches) than are Flying Steamer-ducks (length 68 cm or 27 inches).  Their larger size probably evolved as an advantage for territorial defense of food and young, and possibly for increased warmth when diving in cold waters.  Speaking of territorial defense, steamer-ducks have evolved hard "knuckles" on the wrist bones of their wings, visible in the main photo, above, of the Flightless Steam-duck, as an orange spot.  Steamer-ducks, in fact, can be viciously aggressive and cause real hurt when throwing wing-punches, and can cause mortality in other species. There are actually four species of steamer-ducks, all belonging to the "Southern Cone" of southern South America, where many other interesting evolutionary experiments have arisen.  The Flying Steamer-duck pictured here is the only one that has retained the power of flight; however, it does  not take to wing very often.      A Flying Steamer-duck about to take off ... or at least attempt to.    So how on Earth did these flightless species evolve?   Usually, flightlessness in birds develop because they occur on islands that lack predators, and thus they do not need to take to wing to escape danger.  However, this is not the case with our flightless duck friend here, which evolved flightlessness probably because its local habitat is habitable year-round with adequate food, shelter, and resources ... and thus, there was no need to migrate (fly) to other environments during part of the year.  Perhaps one day, the Flying Steamer-duck may also lose its power of flight for the same reason.  So this entire complex of steamer-ducks represents a marvelous example and model of different stages and dynamics of the evolution of flightlessness.       Information:      Fulton, T. L., B. Letts, and B. Shapiro. 2012. Multiple losses of flight and recent speciation in steamer ducks. Proceedings of the Royal Society B: Biological Sciences 279(1737):2339-2346.       Livezey, B. C., and P. S. Humphrey. 1986. Flightlessness in Steamer-ducks (Anatidae: Tachyeres): its morphological bases and probable evolution. Evolution 40(3):540-558.       Nuechterlein, G. L., and R. W. Storer. 1985. Aggressive behavior and interspecific killing by Flying Steamer-ducks in Argentina. Condor 87:87-91. Note that the Fulton et al. publication, above, suggests that the flightless Falkland Steamer-duck (Tachyeres brachypterus) is genetically indistinguishable from the Flying Steamer-ducks on the Falklands, and that the genetic taxonomy of the entire steamer-duck complex is still unclear.