Student Prize Award Abstract
1997 Oral Paper Award

INTERACTIONS BETWEEN ENERGY BALANCE, HORMONAL PATTERNS AND MATING BEHAVIOR IN WILD BORNEAN ORANGUTANS (PONGO PYGMAEUS)

C.D. Knott
Department of Anthropology, Harvard University, Cambridge, MA 02138

This study investigated the hypothesis that changes in energy balance have a significant effect on orangutan hormonal functioning and mating behavior. Data were collected on wild orangutans in Gunung Palung National Park, Indonesian Borneo, starting in August 1994 and are based on 8000 hours of observation of 60 animals. Orangutan feeding and activity patterns were monitored, and foods were collected and analyzed for metabolizable energy. Energy balance was assessed through changes in caloric intake and the presence of urinary ketones (indicating fat catabolism). Changes in fruit availability were monitored in 558 orangutan fruit trees. Non-invasive methods of collecting and preserving urine were developed and urinary estrone conjugates (E1C) were measured using radioimmunoassay for hormonal evaluation. Mating was broken down into component behaviors. Results revealed significant (p=.001) fluctuations in fruit, leading to dramatic changes in diet and caloric intake (p=.0003). Ketones were present in significantly more urine samples during fruit shortages (p=.0002). During periods of high fruit and positive energy balance, estrone conjugates were significantly higher (p <.05) than during fruit poor periods. These data suggest that changes in energy balance, due to dietary shifts have a significant impact on ovarian function. All matings were observed during periods of high food availability and higher average E1C levels. Most copulations were with sub-adult males and could not be easily categorized as "forced" vs. "consensual."