I realize that having a pet peeve about faunal indices puts me at the top of the all-time nerd list. Since that ship has sailed, I might as well expound:
For any non-zooarchaeologists who might stumble upon this blog, a faunal index is a proportion of one type of animal out of some subset of the total faunal assemblage, used to explore changes in an aspect of diet or landscape use. For example, coastal archaeologists may use an index of the number of specimens of fish remains divided by the total fish added to all terrestrial mammals, as a measure of how important marine resources were in the diet. A very common faunal index is some variant of Bayham's (1982) original Artiodactyl Index. Bayham calculated the proportion of artiodacytls (by far the most important big game in the Southwestern context in which he was working) out of the total number of artiodactyls and rabbits (by far the most numerous prey species). Often, this type of big game index is calculated for a diachronic sequence, and changes in the index are interpreted as measures of changing foraging efficiency, with the increasing use of small game considered evidence for resource intensification.
There is nothing wrong with the use of indices (I use them myself all the time), but it's very important to remember that their interpretation is based on their archaeological context, not on trends documented within the faunal assemblages themselves. Changes in faunal indices can only be understood with a clear understanding of site function and the regional archaeological record. Bayham's (1982) study is the perfect example of this. Within the context of Ventana Cave, Bayham documented an increase in large-game use through time. He interpreted this not as an improvement in foraging efficiency but as a change in site function. What had been a base camp in the Archaic had become a specialized hunting camp in later periods. Therefore, the proportion of artiodacytls increased. This took place, however, during a period of clearly recognized economic intensification on a region-wide scale. Ergo, more artiodactyls = greater intensification.
Speth and Scott (1989) built on Bayham's work, discussing changes in labor organization that could lead to increases in the Artiodactyl Index, such as the ability of some men to forego agricultural work and specialize in hunting when populations reach a threshold size and organizational complexity. In the Southwest alone, there are several examples of increasing proportions of artiodactyls in assemblages, despite clearly documented economic intensification (ex. Cannon 2003; Dean 2006; Potter 2000). These are interpreted in various ways (evidence of specialization, importance of feasting behavior in larger social groups, etc.). Very seldom are they interpreted as evidence of increased foraging efficiency (although occasionally the argument is for climate amelioration.) I can think of many other examples in other regions of the world, although this question has been particularly well studied in the western United States.
My point is merely this: zooarchaeologists should not cite internal zooarchaeological evidence alone when interpreting faunal indices. To do so is not so much naive as unrealistic. None of us are actually using the theoretical underpinnings of these indices as the basis for our interpretations. Instead, we are using our understanding of the broader archaeological record, and we should be upfront about that. Theory alone is not driving our interpretations of these indices. We are using the indices to find the time period and degree of change, not to tell us what direction of change occurred.
1982 A Diachronic Analysis of Prehistoric Animal Exploitation at Ventana Cave. PhD Dissertation, Arizona State University, Tempe.
2000 Large Mammal Relative Abundance in Pithouse and Pueblo Period Archaeofaunas from Southwestern New Mexico. Journal of Anthropological Archaeology 19:317-347.
2006 Hunting Intensification and the Hohokam "Collapse". Journal of Anthropological Archaeology 26: 109-132.
2000 Pots, Parties, and Politics: Communal Feasting in the American Southwest. American Antiquity 65:471-492.
Speth, J.D. and S.L. Scott
1989 Horitculture and Large-Mammal Hunting: The Role of Resource Depletion and the Constraints of Time and Labor. In S. Kent, ed., Farmers as Hunters: The Implications of Sedentism, pp. 71-79. Cambridge University Press, Cambridge.