DR. CLAUDIA R. VALEGGIA, CONICET, Formosa, Argentina, was awarding a grant in May 2003 to aid research on 'Fertility Patterns and Energy Availability of Foraging Wichi in the Argentine Chaco.' This study was part of the Chaco Area Reproductive Ecology Program, a long-term project that seeks to understand the interactions between environment, behavior, and reproductive biology of foraging groups in the Argentine Chaco. The aim of the study was to collect baseline data on how demographic and fertility patterns of Wichí people (n = 800) relate to changes in seasonal variation in energy availability and foraging practices. Preliminary results indicate a high fertility rate (8.6 births per woman), a relatively short inter-birth interval (average: 2.3 months 3.6) and a high infant mortality rate (46%). A birth seasonality effect was evident, with conceptions taking place between April and July. The Wichí of these communities were in good nutritional status, only 2% of adults (all women) were considered undernourished. Furthermore, there was a considerable percentage of overweight and obesity. As many as 55% of men and 54% of women were overweight (Body Mass Index > 25), whereas 17% of both men and women were obese (BMI >30). There were no apparent differences in energy availability across the annual cycle. However, there was considerable seasonal variation in the frequency and type of subsistence activities and in diet composition. A marked sexual division of activities was also evident and that seems to explain the differences in energy availability between women and men. Further analyses will explore the interaction between seasonality, division of labor, and fertility.