Eagle Nest Taphonomy - California Style
Hot off the press – Jon Erlandson and colleagues, in a 2007 Journal of Archaeological Science paper, describe their taphonomic analysis of an eagle nest faunal assemblage. Their report provides some fascinating comparisons for our Aniakchak “coastal critters” study. Their eagle nest was a massive stick structure found on Ferrelo Point in California’s Channel Islands. They suggest this nest was in use from around 1850 until 1940, so it is both historical and long-lived. Given this long use-life it is perhaps not surprising that they were able to collect nearly 10,000 faunal elements. (I’ve got to get Ross and Linda to tell me how many fish and bird bones we have from the Aniakchak nests, but I’m guessing just a couple hundred.)
Erlandson et al. conclude that
The Ferrelo Point eagle midden clearly demonstrates the ability of bald eagles to create substantial middens containing thousands of fish and seabird bones, as well as smaller quantities of shellfish and pinniped remains (p. 268).
They found few distinguishing characteristics, noting that
For birds, the presence of talon marks on a few bones is an obvious signature, but most of the bird bones and nearly all of the fish and mammal remains were not obviously modified (p. 269).
So how do we tell eagle middens from archaeological middens? We can’t necessarily argue that certain food remains are unique to human sites. As Erlandson et al. note, the presence of large abalone shells in the Ferrelo Point midden contradicts those who claim these heavy shells are found inland only as the result of human transportation. Likewise the fact that they found pinniped bones indicate that we need to interpret mammal remains with caution. (Erlandson et al. say that all their pinniped remains were all from newborn or stillborn pups. So bones from more mature seals and sea lions may still be unique to human middens.)
The three characteristics that I think offer the best hope for resolving this taphonomic problem are the relative frequencies of bird remains, relative frequencies of whole versus broken bones, and skeletal part frequencies. Both the Ferrelo Point analysis and other eagle foraging studies cited by Erlandson indicate that birds compose a relatively high proportion of the eagle diet. Bird remains accounted for 52.9 percent of the identified bones (NISP) in the Ferrelo assemblage. The studies they cite from Alaska indicate that birds comprise as much as 83 percent of the animals harvested by eagles in our region. My impression is that coastal Alaskan archaeological faunal assemblages, in sharp contrast, do not contain more than 10 or 20 percent bird bones. I’m sure there are some exceptions, but this might be a good start.
Bone breakage patterns and skeletal part frequencies may hold even greater promise as taphonomic indicators, but I’ll hold off on discussing these issues for another post.
An obvious difference between eagle and human middens is that human middens usually contain fire cracked rock, some charcoal and artifacts in addition to the fauna. I’ve personally never seen a human faunal midden that was pure fauna.
patrick
Brian,
Another comment I just thought of -
Maybe there is a stratigraphic difference between the two types of middens as well – eagle middens created piecemeal while human middens created by dumps of material. Middens I’ve excavated had layers of urchin, then FCR etc. I’d think eagle or any animal midden would be much more homogenous and mixed without individual layers or ‘dumping’ episodes.
In any case, I’ll have to read the article!
Patrick
Hey Patrick, I agree that cultural middens in Alaska are so obviously of human origin that the question would be silly to even ask. Erlandson and Moss, however, have raised this issue largely in the context of determining the origin of small middens found in Pleistocene sediments in coastal California. The debate is whether these “middens” were created by humans (indicating a pre-Clovis occupation), or by natural agents. I think our taphonomic study will add to the literature on this debate.
The question for Alaskan archaeologists is whether non-human animals had any role in creating the midden sites we investigate. The Aniakchak eagle nest is on an archaeological site, so presumably some of the faunal remains we recover in our excavations could be the result of eagle predation. I think it will be interesting to see if we can pick up any eagle signature when we compare the midden samples from site areas near the nest with site areas further away. I’m willing to bet, though, that the amount of fauna that is of anthropogenic origin overwhelms all other sources at most of our sites.
Another interesting aspect to this issue was raised when we attempted to excavate a small test near a known eagle roost to see whether there was any subsurface fauna to be found. Ross did this excavation which he located about 500 m offsite. He told me that there wasn’t much of anything in the sod and first five cm of soil. Then the fauna started to increase including some whole razor clam shells, and even some large mammal ribs. Finally he hit some historic artifacts (probably 20th century). So apparently in this case we think some humans contaminated our eagle roost midden!
Afarensis has the just published the second issue of the Four Stone Hearth!…
Afaranesis has just published the second issue of our anthropology blog carnival, the Four Stone Hearth. Again we have had an excellent turn out, spanning a lot of the known blogosphere that I frequent. I am really impressed by the turn out and hope yo…