Old Dirt - New Thoughts

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.

We just submitted an abstract for a poster session in the 2007 SAA meetings.  Our poster will present our taphonomic studies of the shell and bone accumulations found with the eagle nests and otter den in Aniakchak Bay. Our goal for this analysis is to identify the distinctive characteristics of these non-human created ”middens”.

 Ross collecting eagle nest fauna from abandoned nest at Elephant Head Point.

One intriguing observation we made in the field came when we watched the eagles at SUT-027 bringing salmon up to the nest. Twice we noticed that the eagles first removed (ate?) the head off the fish before carrying the rest of the body up to their fledgling. I don’t know why they removed the head (perhaps to lessen the weight they had to carry), but if they did this regularly then their “midden” would have the same salmon body part pattern as human sites where only the salmon fillets are transported from fish camps to the main villages.

  Headless pink salmon dropped by eagle below nest at SUT-027.

We were inspired to undertake this project in part by the 2001 article in American Antiquity by Erlandson and Moss where they discuss the many different creatures that are potentially involved in forming coastal faunal assemblages. In their article they provide data they collected on an eagle nest in southeast Alaska. I think our data should be a very interesting addition, especially since we have collections from “ground” nests. I’d like to hear about any other reports of eagle or otter fauna.