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."
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