faunal indices revisited

Codding, Brian F., Douglas W. Bird, and Rebecca Bliege Bird
2010 Interpreting Abundance Indices: Some Zooarchaeological Implications of Martu Foraging. Journal of Archaeological Science 37:3200-3210.

After the post on my faunal index pet peeve, I just had to comment on this article in JAS. Very roughly, the article can be summarized as "we have ethnographic data that shows that people eat more big animals when they're more common, and fewer big animals when they're rare", but with the caveats related to failure rates that you would expect, given the authors' previous publications. I have no problem with their data, their methods, or their conclusion.

My concern with the article lies in their stated opposition to alternative interpretations of large-game indices. Here's the relevant passage (from page 3201):

However, ethnographic and actualistic work has questioned the assumption that prey body size and prey rank are always positively correlated. Mass capture techniques may increase post-encounter return rates for some types of small prey, particularly fish and insects (Madsen and Kirkman, 1988; Madsen and Schmitt, 1998; Ugan, 2005a,b; Lupo and Schmitt, 2002, 2005). Moreover, under
some circumstances, larger prey may be of lower rank than predicted due to the effects of relative prey mobility, which can increase with prey size, and may lead to higher instances of pursuit failure (Bird et al., 2009; see also Hawkes et al., 1991; Jochim, 1976; O’Connell et al., 1988; Smith, 1991:230e231; Stiner et al., 2000; Winterhalder, 1981:95e96). If this is the case, foragers may attain higher overall return rates by pursuing smaller prey that can be acquired more reliably. Because foragers (often men) continue to pursue larger prey despite the acquisition risk, it may be that the actual goals of foraging vary as a function of gender (Jochim, 1988), with men focused on maximizing currencies other than the rate of resource acquisition, such as social capital or prestige (Bliege Bird and Smith, 2005; Hildebrandt and McGuire, 2002). Instances of such behavior represent a clear violation of one of the primary assumptions of the PCM (e.g., Bliege Bird et al., 2001; Hawkes et al., 1991; Hill et al., 1987; see also Lee, 1968).

With this critique, an alternative interpretation of abundance indices has emerged in opposition to the traditional interpretation. This alternative view suggests that high proportions of large prey relative to small prey represent lower overall foraging efficiency (e.g., Hildebrandt and McGuire, 2002; McGuire et al., 2007) and a gender division in foraging labor in which men’s pursuit of large prey is subsidized by women’s labor focused on more reliable resources (Hildebrandt and McGuire, 2002; McGuire and Hildebrandt, 2005). Accordingly, diachronic declines in the abundance of larger prey relative to smaller prey then reflect increases in foraging efficiency and an increase in the overlap between men’s and women’s resource choice, both being focused on small prey (McGuire and Hildebrandt, 1994, 2005; but see also Jarvenpa and Brumbach, 2009; Kuhn and Stiner, 2006; Waguespack, 2005; Zeanah, 2004).

The authors then state that opposing interpretations of large-game indices will lead to hypotheses about prehistoric foraging being untestable, but that Martu ethnographic data, while not reflecting all variation in hunting, can at least elucidate the basic ties between prey size, foraging returns, and hunting decisions. Their conclusion, as stated above, is that decreasing large-game use is, indeed, evidence for decreasing foraging efficiency, and not the other way around.

Alas, the authors committed my number one faunal index pet peeve: they ignored context.

1) The authors cite Hildebrandt and McGuire as perpetrators of the hypothesis that increasing large game indices represent decreases in foraging efficiency. I can't speak for them, but that's not how I've read their work. Hildebrandt and McGuire (along with several other zooarchaeologists who were not cited in the article, including me!) argue that in certain contexts the increased hunting of large game represents a decrease in foraging efficiency. For example, if large game is important for ritual use, then large game may be more common during periods of high social stress, even though hunting that large game requires less efficient foraging decisions than hunting small game. Another example would be if agricultural labor constrained mobility and settlement locations, and kept hunters from easily accessing areas where large game was prevalent. There, too, an increase in large game would represent a decrease in foraging efficiency, reflecting the need for long-distance hunting as more local protein sources proved inadequate.

2) Since the argument that increases in large-game indices may reflect decreased foraging efficiency is strongly dependent on context, proving that is not the case in one context is not the same as proving that is never the case. The logic is problematic.

3) The authors state that "if both interpretations are taken seriously, competing hypotheses about prehistoric foraging are rendered essentially untestable." This is not true. The competing hypotheses are tested by looking at the archaeological context. As I stated in my previous post, faunal indices do not prove anything in and of themselves, they must be interpreted in light of their archaeological context. We must look at changes in settlement patterns, technology, and other aspects of the economy to know whether economic intensification or food stress manifest during the period in question. If we know so little about the prehistoric societies that produced these faunal assemblages that we cannot even tell if they are undergoing population growth, or community coalescence, or agricultural intensification, then we should probably re-think our understanding of the faunal indices, as well.

I will now re-state my opinion on faunal indices. Perhaps I should call it Palimpsest's First Law: Faunal Indices tell us about the timing and intensity of change, but they do not tell us the direction. For that, we need to know their context.