In looking into recent research on Southwestern turkeys, I found an interesting paper from 2007 by E. Bradley Beacham and Stephen R. Durand about turkey eggshell. Specifically, they came up with a new technique for analyzing archaeological eggshell to determine whether or not the egg had hatched. The idea behind it, confirmed by an experiment they did with modern wild turkey eggs, is that bird embryos take the material to develop their skeletons from the interior portion of their eggshells, so the longer an embryo has been developing in the egg the more reduced the inside of the shell will be. This is clearly apparent in microscopic examination of modern eggshells. The usefulness of this technique is that it can theoretically determine if turkeys were being bred, as opposed to simply being kept captive, if large numbers of eggs had hatched. Beacham and Durand connect this to a longstanding dispute in Southwestern archaeology over how to interpret the evidence of archaeological turkeys, with one side arguing that turkeys were introduced from Mexico as already domesticated animals, with the wild turkeys currently known in the Southwest possibly descending from escaped domesticated turkeys that went feral, and the other side arguing that turkeys were domesticated in the Southwest from local wild turkeys, possibly quite late after many years of having been captured in small numbers for their feathers but not bred. We now know from genetic evidence that both of these theories are wrong, although the former is apparently closer to being true, and it now seems that turkeys were introduced as domesticated animals, probably from the east rather than the south, and that this happened quite early, at least by Basketmaker II and possibly during the Late Archaic.
The archaeological eggshells Beacham and Durand analyzed using this technique were from two rooms at Salmon Ruin, a major Chacoan outlier on the San Juan River near present-day Bloomfield, New Mexico. These rooms were excavated in the 1970s, and they were selected for this analysis because they contained significant quantities of well-preserved turkey eggshell. Eggshell is very fragile and needs very good preservation conditions to survive, so the excellent preservation conditions at Chacoan great houses like Salmon are important in doing this kind of research. The sampled shell fragments came from strata clearly identified with the three originally designated periods of occupation at Salmon: Primary or Chacoan (ca. 1088 to 1125 AD), Intermediate (ca. 1125 to 1190), and Secondary or Mesa Verdean (ca. 1190 to 1280). These turned out to have quite different results. The Primary shells overwhelmingly showed no evidence of having hatched, and little evidence of having held embryos long enough for material to be taken from them at all. The Intermediate shells, on the other hand, mostly did show evidence of having held embryos for significant periods, and about half of them seem to have hatched. The Secondary shells, most of which came from a different room from the other two samples, were more like the Primary ones in that they showed little evidence of embryo development and almost none of hatching.
This is odd, and hard to interpret in terms of domestication or intensity of use. The sheer amount of Secondary eggshell throughout the site, compared to the much smaller amount from earlier periods, suggests increased use of turkeys during the thirteenth century, which is consistent with evidence from throughout the Southwest showing increased turkey use, especially for meat, during this period. The shell evidence, however, while it does show that breeding seems to have taken place during the Intermediate period, doesn’t really fit with this increased overall use. It’s possible that this is simply due to a sampling issue, and that further study of a larger sample of Secondary eggshell would show more evidence for breeding. It is also possible, as Beacham and Durand note, that this increased use of turkeys involved the consumption of eggs as well as meat, and that the Secondary sample analyzed is associated with this use of eggs rather than with breeding. Something similar may also be going on with the Primary sample, although Beacham and Durand, who clearly seem to favor a late onset of breeding and domestication, prefer to see it more as evidence that turkeys were not yet fully domesticated at that time. As noted above, however, the genetic evidence argues strongly against this interpretation.
Given the genetic evidence, it is not clear how to interpret the eggshell evidence in this paper, but it offers an interesting new way to look at turkey eggshell in well-preserved contexts, and give the frequency of these contexts in the Southwest further use of the technique may further refine our understanding of the issues surrounding turkey use in the prehistoric Southwest.
BEACHAM, E., & DURAND, S. (2007). Eggshell and the archaeological record: new insights into turkey husbandry in the American Southwest Journal of Archaeological Science, 34 (10), 1610-1621 DOI: 10.1016/j.jas.2006.11.015