Chickens were brought to South America in Precolumbian times by Polynesians.
It's all over the wires, so I'll just point to John Noble Wilford:
That is the conclusion of an international research team, which reported yesterday that it had found "the first unequivocal evidence for a pre-European introduction of chickens to South America," or presumably anywhere in the New World.
The researchers said that bones buried on the South American coast were from chickens that lived between 1304 and 1424. Pottery at the site was from a similar or earlier time. A DNA analysis linked the bones, which were excavated at El Arenal on the Arauco Peninsula in south central Chile, to chickens from Polynesian islands.
About half the news articles seem to be leading with, "Why did the chicken cross the Pacific Ocean?" This one is no exception. Har, har, groan.
I don't really have much to say about it, it seems like a very straightforward discovery. There is a radiocarbon date and the DNA evidence. Also, the early postcontact historical record corroborates:
Others thought [chicken arrival with the Spanish] unlikely, noting that when the Spanish invaded Peru in 1532, they saw chickens being used in traditional ceremonies. It seemed hard to believe, some scholars pointed out, that chickens would have been so rapidly dispersed from the east coast to the west and already be incorporated in religious events.
Charles Mann's book 1491 doesn't review this example, but it does talk about analogous kinds of early post-contact documentary evidence from New World peoples. It seems to be an increasingly important source of information to corroborate archaeological findings.
And the chicken transfer does help to explain the sweet potato problem:
The presence of the South American sweet potato in pre-European sites in Polynesia indicated some prehistoric contact between America and the islands.
I've never understood why this has been so quickly waved away. I mean, just last month this Nature News article reviewed a study that claimed that sweet potato seeds could have traveled to Polynesia on a free-floating unmanned ship.
Good grief. I suppose the chickens manned the boat. Er, chickened the boat?
Foods like these have to be among the fastest things to diffuse, even given relatively rare population contacts -- and certainly the Postcolumbian exchange between New and Old Worlds demonstrates this. I suppose the most negative evidence is the lack of evidence for other South American crops, like maize. Maybe the sea travelers used it all to feed the rats?
I mean, rats made it as far as Easter Island, why not the next step? Maybe some South American rats are actually Precolumbian also?
The only thing faster is disease -- and fortunately for the Americas, eastern Polynesia didn't have many of those to transfer.
Wilford's article ends with this:
Scholars found it disappointing and puzzling that the Polynesians who landed at El Arenal left nothing more than chicken bones. Pottery at the site is in a local style. Perhaps the visitors ate and ran, but not without leaving behind some starter chickens for future plates of arroz con pollo.
This seems quite obvious: the chickens were introduced a lot earlier than 1304. They would perhaps have been the longest-lasting element of the cultural transfer -- they wouldn't even have necessarily required permanent settlements, although a more substantial presence might well have occurred. Chickens are the most sensitive sign we can expect to see, just as sweet potatoes are the most sensitive sign on the other side of the contact. You aren't going to find the one place where Polynesians showed up -- you are going to find some site 500 years later when the chickens have spread across half the continent.