Posted by: Rob Viens | September 17, 2013

Swan Lakes on the Pampas

By September 14, Darwin’s new traveling companions had arrived and they all set out for the next Posta.  He described the trip in his diary:

“As the men belonging to the next Posta meant to return, we should together make a party of five & all armed, I determined to start & not wait for the officer. — After galloping some leagues, we came to a low swampy country which extends for nearly 80 miles to the Sierra Tapalken. — in some parts there are fine damp grass plains; others black & rather peaty & very soft. — many extensive fresh water but shallow lakes, & large beds of reeds; it resembles the better part of the Cambridgeshire Fens. — This Posta, being a very long one, each of us had two horses; Having passed many swamps, we found a dry spot & there passed the night.” (Sept 14)

“Rose very early in the morning; passed in the road the 4th Posta, where the men were murdered. — The Lieutenant, when found, had 18 Chusa wounds in his body. — Arrived in middle of the day at the 5th Posta. — Here are 21 men, as it is the central & most exposed part of the line of Postas. — The Rancho is built on the edge of a large lake, teeming with wild fowl.— amongst which the black necked swan was conspicuous. There was some difficulty about horses so I determined to sleep here. — In the evening the soldiers returned from hunting, bringing with them seven deer, 3 ostriches & 40 of their eggs. — many partridges & Armadilloes.— It is the constant habit of the soldiers wherever they go to fire the plain; we made several fires, which at night were seen burning with great brilliancy. — they do this to improve the pasture & perhaps also to puzzle any straggling Indians. — Slept in the open air, as the Rancho consisted only of an enclosure of reeds, without any roof.” (Sept 15)

Black-necked swan (from Wikipedia Commons):

black-necked swan

The Black-necked swan (Cygnus melancoryphus) is native to South America. At up to 15 pounds (~7 kg) and 50 inches (~125 cm), and sporting a wingspan up to about 70 inches (~175 cm), the black-necked swan is the largest waterfowl in South America. The region of the Rio de la Plata appears to be a winter migration zone (which explains why Darwin saw them at the end of the southern winter.  They spend the summer season further south in and around Tierra del Fuego and the Falkland Islands. Much like the travel habits of Darwin while he was in South America!

There are 6 or 7 swan species (in the genus Cygnus) found around the world (one is listed as a subspecies by some taxonomists).  Most are found throughout the Northern hemisphere, though along with the single South American species, there is also a black swan from Australia (and now New Zealand). There is apparently a rich fossil record of swans, which suggests that they originated in eastern Europe/western Asia back in the Miocene (~25 million years ago). So not only did our black-necked friends migrate seasonally like Darwin did, they also “traveled” to South America from the same general part of the world. (RJV).

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