Tuesday, March 18, 2008

Clovis Overkill Didn't Wipe Out California's Sea Duck
Clovis-age natives, often noted for overhunting during their brief dominance in a primitive North America, deserve clemency in the case of California's flightless sea duck. New evidence says it took thousands of years for the duck to die out.

A team of six scientists, including Jon M. Erlandson of the University of Oregon, pronounced their verdict in the Proceedings of the National Academy of Sciences (online, March 13) after holding court on thousands of years of archaeological testimony taken from bones of the extinct sea duck uncovered from 14 sites on islands off the California Coast and 12 mainland sites from southern California northward.

The link there says that the paper is available for free on the PNAS web site but when I tried to get at it, it would only do so if I purchased access. Happily, I have university access. I'm going to read the paper in the next couple of days, but they also have a short essay accompanying it by Don Grayson (refs below). He writes, in part:
This work establishes that people coexisted with, and fairly obviously preyed on, a flightless, ground-nesting bird for some 8,000 years. In the Greater Antilles, there is strong evidence that people coexisted with ground sloths for 1,000 years (14). We are thus now learning that rapid extinction is not the only possible outcome for such vulnerable species as flightless ducks and huge sloths, even if it is a common one. We are also learning that late Pleistocene species that became stranded on islands did not always require a human presence to end their existence. Mammoths became extinct on St. Paul Island in the Bering Sea after 5,700 14C years ago even though people did not arrive there until historic times (15, 16). A similar event occurred in Ireland and on the Isle of Man, where the giant deer Megaloceros was lost shortly after 11,000 14C years ago, again before people arrived (17).

It is all so much more complicated than we thought only a few years ago. What has made the difference is the construction of individual species histories. Rather than assuming that everything was lost at the same time and for the same reason, an assumption that is still routinely made for North America, focusing on the histories of individual species takes into explicit account the fact that, as Henry Gleason (18) once put it, every species "is a law unto itself." Paleoecologists and ecologists alike now recognize that "Gleasonian individualism" is the general rule, not the exception. If that is the case, the knotty problem of understanding the North American extinctions is not likely to be solved until each species involved has been provided with its own history. This process is well under way in Eurasia, but has barely begun in North America (19).

True enough. The chronology of each species' extinction is differently attested as is their role in human predation.

UPDATE: reading the paper now. This is the crux of what they're doing:
The bird’s persistence into the Holocene was generally
attributed to a relatively recent development of watercraft by
Native Californians (10). Once good boats became available,
California Indians were able to reach the islands, islets, and
offshore rocks the birds used as breeding colonies—then exploit
them into extinction.
Archaeological data from the last decade provide new insights
into the antiquity of watercraft use along the California coast
that have important implications for the chronology and duration
of Chendytes’ exploitation.

If people were not out in the Channel Islands until relatively recently AND the duck went extinct shortly thereafter, it makes a fair circumstantial case for humans causing the extinction. OTOH, if they can be shown to have been there AND using them as part of their subsistence for a long time before that, it doesn't absolve humans from a role in the extinction, but it basically nullifies the blitzkrieg model. (I posted this article some time ago)

They provide dates for the earliest secure exploitation >10k BP and that "by at least 7,500 calendar years B.P., coastal peoples had a significant presence throughout the duck’s California range and regularly exploited them. . .". They also put the youngest direct date at 2,720–2,350 calendar years B.P. Thus, humans had been exploiting them for at least 8,000 years.

They relate this study to that of megafauna generally:
Our archaeological chronology for the extinction of Chendytes shows
that exterminating even such a vulnerable species from continental settings took millennia of hunting by Native Americans. In contrast, Clovis peoples show no sign of such prolonged exploitation on a larger continental stage.

. . .

Along the continental mainland of North America, the protracted span of hunting that led to the extermination of Chendytes lawi contrasts with both the insular situations and megafaunal extinctions as envisioned in the Pleistocene overkill hypothesis. The Chendytes record is consistent with the Eurasian situation in suggesting that the extermination of entire populations from continents, particularly multiple species, should have been protracted and archaeologically visible if overhunting was the sole or primary cause.

It's particularly interesting because the island model of rapid extinctions has been used as a model for continental extinctions. In this case at least, an insular species survived well after human contact. They don't go into it in great detail, but one wonders if perhaps rats were missing from this equation. Terry Hunt and colleagues have argued that rats had a large role in the degradation of Easter Island. If humans were only partially exploiting this species as a relatively small part of their diet -- especially if the species were spread out over a number of reasonably inaccessible islands -- then one might expect extinction to take longer. If rats had fully colonized all or most of the islands along with the humans, that might have sent them to the brink quicker.

Um, just speculation on my part. I'd like to see a lot more on the exploitation patterns. Good stuff though.