Posted by: Rob Viens | July 20, 2013

The “Mus is Loose” on Gorriti Island

The ballast recovered for the Adventure was hidden on Gorriti Island, located just off the coast of Punta del Esta (due south of Maldonado). Today this island is a nature reserve and popular tourist destination.  But in the past, the small island (about 1.5 by 0.5 km) has served several functions.

The island, originally known as Las Palmas for its palm trees, was supposedly visited by several explorers before Darwin – including Ferdinand Magellan and Francis Drake. Later (after Darwin’s visit) it became the site of a hospital and quarantine zone during the cholera epidemic.  At some point, the name of the island was changed to Isla Gorriti after José Francisco Gorriti – an Argentinean independence fighter and governor of the city of Salta.  He died just 3 years before Darwin’s visit in 1830.

Isla Gorriti – check out that nicely foliated metamorphic rock along the shore! (from

gorriti island

During his visit to the island, Darwin noted (and collected) one of the island’s primary residents – a critter he identified as Mus decumanus. Here is what he had to say about this little mammal:

“Was killed at the Island of Goriti where they are said to be common.— They are also said to be occur in numbers at East Point.— They inhabit burrows in the sand dunes.— It is a likely place for ships to leave this animal, if they are infected with such monsters.— But I think from habits it is an aboriginal.— The occurrence at Island Goriti is no difficulty as a reef now connects the it with mainland, probably was once continuous.— The ears were whitish & oddly contrasted with rest of body.— An old male weighed 15 & ¾ oz:” (Zoological Notebook)

What was this little resident of Isla Gorriti? The description is relatively short, but all the information points to the “monster” being the most successful mammal species on the planet (after humans, of course) – the brown rat (Rattus norvegicus). These rats are one of the larger rat species (consistent with the larger weight Darwin recorded) and are known for digging extensive burrow systems. (The scientific name comes from the fact they were originally thought to have been carried to England from Norway. That turned out to be false, but the name stuck.)

Brown rat (from Wikipedia Commons)

brown rat

The brown rat is one of the most common mammal species on Earth – found almost everywhere outside of the polar regions. Prior to human “assistance”, however, the brown rat is thought to have been restricted to Central Asia and/or Northern China. As Darwin notes, by stowing away on ships, our little rattus friends migrated outwards to cover the world. It is by many definitions one of the most successful invasive species in history.

Let’s face it – rats get a bad rap. They are referred to a vermin because they are known to carry disease and eat our food. But I have to say that I have been growing a little found of Rattus norvegicus. I might even go so far as defend them and suggest that we have come to hate rats for being too “human” – to much like us for our own comfort.  For example, we humans certainly carry disease. Remember that one of the issues faced by the Beagle over the past couple years was the fear that they were carrying cholera from England (see Quarantine in the Canaries). Even today, we have elaborate protocols in place to try to prevent the rapid spread of human disease (especially via rapid air travel).  Often times we are not successful. My family suffered a few years ago from the rapid spread of the swine flu.

Like our rattus competitors, we humans started out in one part of the world (in our case, Africa) and rapidly spread to settle and dominate every major ecosystem outside of the polar regions. Like us, brown rats are social creatures. They live in family groups, fight over territory, form hierarchies, play, care for their young, get aggressive when packed into a small space, groom and care for one another and communicate through sound and touch. There are physiological similarities, too – so much so that we have bred the common lab rat from brown rats, and used it to do human medical research and drug testing. In that way alone, the brown rat may have saved more lives that it has taken via disease. So the next time you are turned off by seeing a brown rat scurry past – try to think about how much we have in common.

Meanwhile back on the Beagle

FitzRoy had realized that he just missed the most recent mail boat out of Uruguay, so he decided to chase it down – wanting to make sure he got the latest mail and specimens off to England.  In his diary, Darwin describes the scramble and the “chase” that followed:

“At night the Packet fired guns to tell us she was on her way to Rio: This caused a scene of animation & bustle; for immediately orders were given “hands unmoor ship”. The Captain. — having letters of importance, determined to stand out after her. — We were soon under weigh, & joining the Packet hailed her that we would keep company for a few days.” (July 18)

“A calm & heavy fog, we were obliged occasionally to signalize by guns.” (July 19)

“At noon a boat was lowered with the letters &c & my collections & taken on board the Packet; we then parted company; & are now sailing back for Maldonado.” (July 20)

FitzRoy obviously felt pretty strongly about getting that mail out! (RJV)


  1. Enjoyed Rob’s comments about the rat and the drama of chasing down the mailbox; gee, where was a cell phone when you needed one?

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