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Some hundreds of years ago, all humanity was removed from the Americas. In fact, most humans are gone from the world altogether. In the intervening time, nature has overrun the formerly human dominated landscapes of the former United States.

The area referred to in the title is the lands formerly around New Orleans. Much of it is underwater after a millenium of global warming and sea level rise; but what remains is cypress and tupelo swamp, live oak thickets, and grassy fire-dominated pine savanna. It is hot and humid in the summer, wet all year round, and rarely freezes in the winter.

In short, this is the perfect environment for the capybara. 1000 years was enough time for many Central American animals to migrate up to the swamps and savanna of former Louisiana. Jaguars are here, along with peccaries and brocket deer. In addition, many escaped domestic animals--horses, cattle, chickens--roam the savannah. But the problem with the capybara is that it is starting pretty far away in the Orinoco Delta of Venezuela.

There are two ways the capybara could get from Venezuela to New Orleans. It could walk along the Mexican coast; or it could island hop, spreading across the many capybara-friendly islands of the Caribbean. Can capybaras spread to Louisiana from Venezuela and populate it in less than 1000 years?

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    $\begingroup$ It's to be confirmed but there are allegued sight in Florida. Also they are excellent swimers often found in the water but don't know if they actually enter salt water $\endgroup$
    – jean
    Commented Jun 12, 2018 at 13:25
  • $\begingroup$ I wanted to link a similar animal that has been seen in the area so I think @jean is correct theguardian.com/us-news/2017/oct/31/… $\endgroup$
    – easiersaidthandone
    Commented Jun 12, 2018 at 15:02
  • $\begingroup$ @jean - more than alleged - wildflorida.com/articles/Wild_Capybara_return_to_Florida.php And one was killed on the Santa Fe river (near me) a few years ago too... edis.ifas.ufl.edu/uw438 $\endgroup$
    – ivanivan
    Commented Jun 12, 2018 at 15:48
  • $\begingroup$ How large of a population are you looking for? $\endgroup$
    – HDE 226868 ♦
    Commented Jun 12, 2018 at 16:06
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    $\begingroup$ Do they need to be from Venezuela? Plenty of zoos have capybaras, such as the Baton Rouge zoo about an hour from New Orleans. Not sure if any zoo has enough for a breeding population, but maybe there's a capybara farm somewhere closer than Venezuela? $\endgroup$
    – Giter
    Commented Jun 12, 2018 at 17:38

7 Answers 7

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They are already here.

Capybara in Louisiana. https://www.facebook.com/stevie.cox.165/videos/10155908203265712/

blurry screenshot from video grainy capybara video Louisiana

Capybaras in Florida. capybara in Florida https://www.youtube.com/watch?v=7NXGXrlQ2ZM

Capybara in California. https://www.nbclosangeles.com/news/weird/Paso-Robles-Capybara-127771708.html capybara at water treatment plant, Pasa Robles

People suggest the these capybaras are escaped pets. Maybe. Or maybe they have come through the Bigfoot dimension and are less wary about getting captured on film.

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  • $\begingroup$ Are there enough to breed? $\endgroup$
    – kingledion
    Commented Jun 12, 2018 at 15:27
  • $\begingroup$ You probably would wind up with an evolutionary bottleneck. But that can be good for a story in explaining why the N.Am capys are not exactly like their S.AM ancestors. $\endgroup$
    – Willk
    Commented Jun 12, 2018 at 15:42
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    $\begingroup$ I went on a swamp tour in New Orleans back in 1999, and we definitely saw capybaras. I can't recall exactly what the guide said about them, but I'm fairly certain he said they were growing more and more common and breeding in the wild. $\endgroup$
    – BlackThorn
    Commented Jun 12, 2018 at 22:48
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    $\begingroup$ A beachhead population like this is definitely your best bet, this has happened plenty of times ,even escaped zoo animals have taken root in abandoned areas before. Just look at what is happening to hippos in Colombia. $\endgroup$
    – John
    Commented Jun 12, 2018 at 23:01
  • $\begingroup$ @John I totally forgot about that! Now I'm adding hippos to my story! I wish I could mark this comment as the correct answer! $\endgroup$
    – kingledion
    Commented Jun 13, 2018 at 11:41
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To travel about 7000km (the land route), given that the average capybara moves about 700 metres a day, it would take a lone animal about 10,000 days to make the journey. 27 years walking, they tend to live about 7-10 years, so he's not going to make it.

We're not talking about a lone animal though, we're talking about population spread. This means they don't move 700m a day but rather a distance the diameter of a territory per generation.

Remember though:

Rather sedentary habits allow ranchers to manage capybara without fences

The trouble with moving capybara quickly is you need to move entire groups, fewer than 4 adults together won't raise young, there are no parthenogenesis shortcuts here. So while individuals could be storm-blown on a raft to a new location, or an anomalous individual may walk considerably further than average, you'll need to build up reasonable numbers together to begin breeding.

Groups can be 100-500 metres apart. Breeding age at around 1yr. They're social, up to 100 in a group.

Assuming larger territories towards the edge of the range and smaller territories in the centre, and being optimistic, it could take 2 years for a small group to expand 1km. A very large population could move faster than that over a short period as the groups hit their upper size limits and force new adults out of the territory, but they might then not expand again for a couple of years.

Upper limit for the population to expand that far: Between 7000 and 70,000 years.

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  • $\begingroup$ My bad then: I had severely overestimated the environmental pressure that could push the capybaras to migrate north in a hurry. In relatively stable conditions, your estimate is the most accurate $\endgroup$
    – Valerio Pastore
    Commented Jun 12, 2018 at 13:34
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    $\begingroup$ They are grazing animals meaning they ill keep moving to new areas to feed. Moving only 700m per generation looks very unlikely $\endgroup$
    – jean
    Commented Jun 12, 2018 at 15:26
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    $\begingroup$ Would the Panama Canal significantly hinder their progress? $\endgroup$
    – corsiKa
    Commented Jun 12, 2018 at 16:04
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    $\begingroup$ I don't think this result holds: The biggest problem is that we won't have a continuous swampland from Venezuela to Louisiana. Your estimate is for spreading through ideal or at least very suitable terrain, i.e. swamp. I think much of the middle bit of Mexico won't be; for swamps you need to be more or less level as well as have suitable underground (not bedrock) and climate (sufficient rainfall as dependent on prevailing winds and temperatures). $\endgroup$
    – user3445853
    Commented Jun 12, 2018 at 17:59
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    $\begingroup$ @user3445853: Two species of capybara (neochoerus aesopi and neochoerus pinckneyi) successfully migrated from South America to North America during the Great American Interchange about 3 million years ago. So it's definitely possible for capybaras to get from South America to North America; the question is just how long it would take. (The fossil record doesn't have enough resolution to answer this question, unfortunately.) $\endgroup$
    – Michael Seifert
    Commented Jun 12, 2018 at 20:14
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This doesn't seem like enough time.

What is the driving force for the capybaras to move so fast to somewhere so remote? Animals tend to move into new environments when the current one is overloaded and can no longer sustain the population easily (https://en.wikipedia.org/wiki/Carrying_capacity). So capybaras will need to thrive in their current habitat, then move to a new nearby ecosystem to look for easier sources of food, reach the carrying capacity of that environment then move again. Over and over again until they reach North America.

Given that capybaras live for an average of 10 years and have pregnancies that last for 5 months, this seems like it is going to take a very long time. Turn over is not going to be very fast.

Last I checked Mexico is also a desert and global warming will only make it even more of one. So this is a natural bottleneck for the creatures that will prevent them from passing. You suggested island hopping, but the islands on the path to New Orleans are very sparse and many of them will be under water after sea levels rise like you suggest in your question with New Orleans being squarely beneath the sea.

So to me it seems like they would never make it to North America. By the time they do, they wont be capybaras anymore, but an entirely different species.

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    $\begingroup$ While 7km/year don't seems hard to achieve that desert ill block any capybara unless they start to eact cactus and shrubs $\endgroup$
    – jean
    Commented Jun 12, 2018 at 15:35
  • $\begingroup$ Mexico has deserts including some big ones by the US border, but on the East coast I think there is a lot of water. $\endgroup$
    – user25818
    Commented Jun 12, 2018 at 20:48
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As other answers have noted, 1000 years probably isn't enough time for capybaras to spread from South America to the North American mainland, but they don't need to.

I'd start by suggesting you don't need capybaras unless you really want them. Louisiana already has some pretty big swamp rats, the nutria or coypu, which grow as big as 20 pounds. As that link lays out, they're already a full blown infestation, from an invasive non-native species.

If that doesn't appeal to you, there are already capybaras in the US, and scientists are warning that they're poised to be the next invasive rodent species threat in north Florida (which is very close to Louisiana, of course)... the coypu/nutria having been the previous invasive rodent species in the American south. So, they don't need to migrate from Venezuela, the existing feral population in north Florida just needs to survive and thrive a bit.

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  • $\begingroup$ @user3067860 - There are feral pigs in Florida. I was personally chased by one while biking through the woods in Orlando back in '98. And of course the "Razorbacks" Arkansas made their University mascot probably more than 100 years ago is just another word for "feral pig". $\endgroup$
    – T.E.D.
    Commented Jun 13, 2018 at 13:54
  • $\begingroup$ @T.E.D. Yes, they are already all over the south despite best efforts to keep them in check (it doesn't help that they were imported way before capybara and nutria), just saying if humanity goes away for a couple thousand years... Probably alligators and boas at the very top, then pigs for top mammal in the south unless the bears make a big comeback. $\endgroup$
    – user3067860
    Commented Jun 13, 2018 at 14:06
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There are two ways that capybaras could move a long distance in a thousand years. Both have been observed in nature.

First, they can walk. If the local conditions are right to support them, animal populations can spread very quickly. But, basically, for this to work, you need a continuous strip of dense forest with water covering the whole route. I don't believe that there is anything like that presently between Central America and New Orleans. If there is in your world, then it's perfectly possible for them to spread that far in a thousand years.

(Note that a concentration of predators along the route might act as a barrier.)

The second way they could get to New Orleans is to ride. Storms which produce major flooding regularly float very large rafts of trees and vegetation out to sea, and it's common for there to be animals trapped on the rafts. Most of them -- probably a very great majority -- break apart at sea and everything drowns, while others wander until everything dies of thirst or hunger, but occasionally such a raft gets pushed to an island or another continent and the hitchhikers are in a new home.

There are quite a few cases of island populations where where this is the only known way they could have gotten there, so it happens. What I don't know is the statistics of it and where this could plausibly be expected to happen in a thousand years.

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  • $\begingroup$ mammals are unlikely to be moved via storms, they can't wait out the long sea voyage their water needs are too high. large animals are especially unlikely, ilands are known for lacking mainland megafauna for this reason. $\endgroup$
    – John
    Commented Jun 12, 2018 at 15:46
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    $\begingroup$ Big mammals don't move this way, but small mammals (e.g., monkeys) pretty definitely do, and have even been found living on floating rafts at sea. The biggest issue is whether there is a plausible way for the raft to move far enough for them to survive. For example, see sciencedaily.com/releases/2010/01/100120131159.htm for an example of Madagascar being populated that way. $\endgroup$
    – Mark Olson
    Commented Jun 12, 2018 at 15:56
  • $\begingroup$ to be fair you are talking about small early primates and a time when madagascar was much closer to the mainland and had an usually favorable set of currents to aid them, there is a reason no modern primates have made the trip. $\endgroup$
    – John
    Commented Jun 12, 2018 at 22:33
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Yes, it could.

Based on your description, I have a feeling that tornadoes and hurricanes will be more frequent.

They have the nice (well, depends on the points of view) habit of carrying things around, and it can surely happen that some capybara is carried along the storm. The few which will survive the flight and land close to an island can settle up there, until the next storm.

It's a sort of Monte Carlo based traveling, but I think over a time span of 1000 years it will allow a decent spreading of the capybara around, reaching even Louisiana.

see also rain of animals

Under this hypothesis, a tornadic waterspout transports animals to relatively high altitudes, carrying them over large distances.

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    $\begingroup$ You seem to be saying that a hurricane could blow a capybara through the air: "The few which will survive the flight and land close to an island can settle up there." They do not! No hurricane can keep anything that large airborne for more than minutes. Birds and other flying creatures do get blown long distances, but they handled the "stay int he air" part themselves and the hurricane simply provides forward motion. $\endgroup$
    – Mark Olson
    Commented Jun 12, 2018 at 13:39
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    $\begingroup$ @MarkOlson "Flight" can simply mean "rapid escape", usually in the sense of running away. The Flight of the Earls from Ireland didn't involve them getting on an aeroplane. ;) It's perhaps not quite the right word for getting washed through the water in a storm, but I wouldn't say it's too unreasonable. Although having mentioned flight - I for one would love to see a murmuration of airborne capybaras, flitting nimbly through the trees on their whirring wings and filling the air with their melodeous song... $\endgroup$
    – Graham
    Commented Jun 12, 2018 at 15:17
  • $\begingroup$ If that's what's meant, it would be well to edit the answer to avoid confusion. $\endgroup$
    – Mark Olson
    Commented Jun 12, 2018 at 15:19
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    $\begingroup$ Hurricanes are not tornadoes and have slower winds and less concentrated updrafts. The carrying time in a tornado is measured in minutes -- during which time a hurricane moves less than a mile. $\endgroup$
    – Mark Olson
    Commented Jun 12, 2018 at 15:23
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    $\begingroup$ Everyone knows that tornadoes can transport whole houses over great distances and drop them intact (at least as long as there's a witch underneath to cushion it.) But I've never heard that hurricanes could. $\endgroup$
    – Mark Olson
    Commented Jun 12, 2018 at 18:11
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Nutrias, which escaped from fur farms in Louisiana, are already a major pest around the area. By 1950, there were 20 million of them in coastal Louisiana, before major efforts by humans reduced the population (including paying a $4 bounty on nutria tails). They got to be so much of a problem that one former sheriff of Jefferson Parish sent out SWAT teams to shoot them.

The big herbivorous rodents with spiky fur living in the bayous are therefore probably going to be nutrias. Even if capybaras could make the trip (probably a breeding pair of escaped pets rather than a migration from South America), they would have to compete with the feral nutrias.

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