1. Wyatt Hilyard
M. Scoggin
ANTH 410
March 30, 2013
Review of “Reproductive Parameters of Female Orangutans”
In October 2012, Birute Mary Gadikas and Alison Ashbury published a paper entitled
“Reproductive Parameters of Female Orangutans (Pongo pygmaeus wurmbii) 1971-2011, a 40-
Year Study at Tanjung Puting National Park, Central Kalimantan, Indonesia.” The article details
and summarize observations and data collected concerning female orangutan reproduction,
collected over a 40 year period. For the study, they were concerned with four main reproductive
parameters: age at first reproduction, interbirth interval (IBI), sex ratio at birth, and infant
mortality. The authors applied their findings to several ecology hypotheses, concluding that the
ecological energetics hypothesis (increased diet quality leads to a faster rate of reproduction) is
best supported by the study.
As with many primate studies, this project can be put to use in several different ways. The
information can be used to better understand orangutans and provide superior
conservation/rehabilitation projects in the future. It can also be used for human evolution studies;
due to their close evolutionary and genetic ties to humans, “documenting orangutan life history is
useful for identifying derived features of human life history.”
The methodology of the project seems to be pretty sound. The work was carried out over
the 40-year period by either Galdikas herself or assistants who had been trained by her, which
minimizes drastic differences in methodology and data collection. I imagine there is still some
degree of difference in personal data collection style, but it is kept at a minimum. The largest

2. problem I found, which they point out as well, is that they did not start with the first generation
of mothers from birth. Their ages and age at first reproduction had to be estimated based on
physical and behavioral clues. It is not something that can be fixed at this point, just a margin of
error that has to be considered.
As part of the study, the authors also compare and contrast their site, Camp Leaky in
Tanjung Puting, Indonesia, with a site in Sabah, Malaysia, Sepilok Orangutan Sanctuary. Not
only are the two projects run differently, but they are dealing with two different species and
environments. The orangutans at Camp Leaky are healthier, have higher reproductive rates, and
significantly lower infant mortality rates than those at Sepilok. There are three main factors for
this: different species, different environments, and different provisioning. Camp Leakey's
orangutans are Pongo pygmaeus wurmbii, whereas those at Sepilok are Pongo pygmaeus morio.
It is a slight difference in subspecies due to geographical location, but it is worth noting that they
are thus genetically different.
Galdikas's team provisions the orangutans once a day on what they call a provisioning
platform, which is designed to increase sociality among the individuals and decrease dependency
on the researchers. The project leader at Sepilok believes feeding platforms actually decrease the
health of mothers due to increased social stress and increased exposure to parasites. This ties in
to another facet of the study, sex ratio at birth. The table on page 67 shows the proportions of
males at birth: 0.63 at Camp Leakey, 0.07 at Sepilok (rehabilitants), 0.51 in a zoo population.
This very large disparity is explained by a few factors. The increased stress at feeding platforms
causes the mothers to have a disproportionately high number of daughters to sons. Also, due to
the nature of orangutan life in Galdikas's site, “it is advantageous for mothers at Camp Leakey to
differentially produce male offspring who will emigrate from their natal area rather than females

3. who will remain close by and increase feeding competition around the feeding platform.” About
provisioning, they conclude that the methods of feeding “may play a role in shaping birth sex
ratios, and social connectivity may play a casual role in infant mortality rates.”
I really liked the tables on pages 64 and 65, detailing the age at first reproduction of the
mothers and pertinent data of their offspring. They are well organized and documented, as are all
the tables. All the raw data of the study is very nicely laid out in the whole article; they make
note of cases and data points that were excluded and explain why. They also include the reminder
that the study is not necessarily over: “It is our hope that in the future, as more data become
available, it will be possible to conduct three-way analysis, including third-generation mothers as
their own category.”
In summation, the study seems to have been well planned and executed, as has the article.
I don't see any major flaws in methodology or findings. They conclude that the ecological life
history model is not supported by their study, but it may explain reproductive variation on an
evolutionary scale. The ecological energetics model is much more suited to their study, showing
no problems when applied to both variation between populations within a species, and multiple
generations within a population. I look forward to the findings of this study being applied to
benefit rehabilitation of orangutans, as well as being introduced as new information for human
evolutionary studies.