Posted by: Rob Viens | December 31, 2012

On the Many Uses of a Wing

On the 30th of December the Beagle “remained at anchor”(Darwin’s only entry for the day) and, on the next day he didn’t have much more to add:

“The sun having at last shown itself at the proper time, observations were obtained & as the weather did not look quite so bad we put to sea.” (Dec 31)

Though having lived in the Pacific Northwest for many years, I can understand the tone of Darwin’s diary entry on the last day of 1832.  It is a “special” day when one can see the sun rise in December or January at these latitudes.

For now though, let me take a step back to the end of Darwin’s entry on the 29th where, along with the wigwams, he described some of the birds he encountered along the coast:

“The sea is here tenanted by many curious birds, amongst which the Steamer is remarkable; this [is] a large sort of goose, which is quite unable to fly but uses its wings to flapper along the water; from thus beating the water it takes its name. Here also are many Penguins, which in their habits are like fish, so much of their time do they spend under water, & when on the surface they show little of their bodies excepting the head. — their wings are merely covered with short feathers.” (Dec 27/28/29)

The “Steamer” Darwin describes is a type of duck called the steamer duck (genus Tachyeres). The genus name actually translates as “fast rower”, and the name “steamer” comes from the fact that they move through the water like a paddle steamer boat, using their wings as oars. So Darwin’s description of the “rowing” ducks is quake accurate.

Check out this video of the steamer duck (uploaded to YouTube by groenelantaarn) – alas, I can’t find good footage of them “steaming”:

There are four species of steamer ducks – most are flightless and all are found in South America.  We can rule out the “flying steamer duck” since Darwin notes that his steamers are flightless (though this species is found in Tierra del Fuego). The Chebut and Falkland steamer ducks are found in the regions whose names they bear.  That leaves the Fuegian steamer duck (Tachyeres pteneres) as the most likely species that Darwin encountered. (For more on penguins see Mr. Darwin’s Penguins.)

Fuegian Steamer Ducks – also called the Magellanic Steamer Duck (from Wikipedia Commons):

Fuegian Steamer Ducks

Darwin concludes his entry with another interesting insight – one of many found peppered throughout his diary.  It is another that I think shows the “wheels spinning” in his head, and suggest that , even if it is merely subconscious at this point, he is absorbing much of the evidence that would later prove vital to his formulating the idea of evolution. Keep in mind that the diary is written “on the spot”, so it does not reflect the synthesis of knowledge from the entire journey (which is the case of Voyage of the Beagle).  He writes:

“So that there are three sorts of birds which use their wings for more purposes than flying; the Steamer as paddles, the penguin as fins, & the Ostrich spreads its plumes like sails to the breeze.” (Dec 27/28/29)

I can almost picture him sitting in his cabin, wondering why the common wing of a bird would have so many different uses in different species.  Clearly this was not a coinsidence…

PS – I just started reading Thor Hanson’s book Feathers – a natural history of the feather.  I’m enjoying it so far, and expect that it has a lot of good insights on Darwin’s post today. (RJV)

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