Happy World Orangutan Day- A Brief Review of Recent Research and News

Happy World Orangutan Day. Orangutans, both Bornean (Pongo pygmaeus) and Sumatran (Pongo abelli), are some of my favorite primates. These orange, solitary creatures live a primary arboreal life in the country of Indonesia on the islands of Borneo and Sumatra. They are highly intelligent and one of our closest living relatives. In honor of International Orangutan Day, I thought I'd celebrate with a post on some of the latest orangutan research.

Starting off with some good news: there are more Sumatran orangutans than was previously thought. There are possibly 8,000 more, bringing the total up to approximately 14, 600 individuals. Better methods and techniques are the main reasons behind the increase in numbers with areas previously not surveyed visited and orangutans found at elevations higher than researchers previously thought it was likely they inhabited.

Sumatran orangutans have been classified as critically endangered since they were first listed on the IUCN Redlist. However, Bornean orangutans were previously listed as endangered, until it was announced earlier this year that they have slipped to critically endangered as well. Habitat loss due to palm oil and rubber plantations threaten this species as well as hunting.

Rocky, an orangutan at the Indianapolis Zoo, can reproduce grunting sounds made by humans. He is able to mimic the pitch and tone of sounds made by humans and started mimicking at age eight. When compared to a database filled with the sounds of other orangutans, Rocky is unique. This new finding raises more questions about the development and origin of language in humans and what our last common ancestor with orangutans looked (and sounded?) like.

Another zoo-based study has shown that orangutans have the ability to use past experiences to create new images in their mind about new experiences. This ability is referred to as affective forecasting. Naong, an orangutan housed at a Swedish zoo, is able to guess whether he likes a new juice flavor based on the past juices he's tasted.  Originally given four flavors of juice, once Naong was familiar with these flavors, the juices were mixed together. Naong, if he observed the mixing, was able to guess whether or not he liked the mixed flavors based on his past preferences. This is yet another way humans are not as unique and different from our primate ancestors than perhaps we thought. Although anyone who has spent a significant amount of time observing these animals at a zoo or reading up on them probably won't be too surprised.

An unsettling study shows how just aggressive female orangutans can be. For the first time, researchers have observed the death of a female orangutan due to the aggressive actions of other orangutans. A young, female, Bornean orangutan attacked an older female with the help of a male orangutan for over thirty minutes. The two attackers traded off, with one attacking and the other preventing the victim from escaping. The older female later died as a result of her injuries. While aggressive behavior on this scale is known in chimpanzees, this is the first time such extreme behavior has been observed in wild female orangutans.

To end on a lighter note, a Sumatran orangutan has released his first music single. Playing on the drums and piano while a zookeeper recorded, Kluet is on his way to international fame perhaps. You can purchase the single here. Proceeds are going towards conservation efforts.

To conserve these animals and show your support for them, consider buying sustainable palm oil, being mindful of your overall consumption and energy expenditure, and donating your time or funds to charities that support these magnificent apes, such as Orangutan Foundation International, Bornean Orangutan Survival Foundation, or the Center for Great Apes.

Lemur habitat was changing before humans even arrived

New research from the DNA of mouse lemurs (of the genus Microcebus) has lead to a surprising discovery about Malagasy forests and their ancient past. Madagascar, a large island off the west coast of Africa, is made up of many forests that are presently not connected and haven't been since around the time humans reached the island. The eastern rainforests (green in the image below) are separated from the western, deciduous forests (blue in the image below) by an expanse of grasslands (in yellow). There are multiple theories concerning what the landscape looked liked in the past and why the eastern and western forests are separated, and research from Yoder and colleagues (2016) uses the genetic history of lemurs to tell us more.

Habitats of Madagascar and species locations. 

From Yoder et al., 2016

Some believe that, rather than this disconnect we now see between western and eastern forests, Madagascar was covered in closed-canopy forests prior to the arrival of humans, with humans acting as the primary agents of change. This so-called forest hypothesis maintains that the large expanse of grasslands that experience frequent burning were once forests and their reduction was not natural.Others believe that the grasslands we see today are similar to ancient grasslands found in Madagascar. Thus, the landscape was not so radically different from the present. This is referred to as the grassland hypothesis by Yoder and colleagues (2016). Finally, another idea termed the mosaic hypothesis by Yoder and colleagues (2016) suggests that the central part of the country was covered with a mix of wooded savanna and closed-canopy forests.


Some of the world's top lemur experts have provided us with new information on the history of Madagascar's forests. Yoder and colleagues (2016) looked at the DNA of five different species of mouse lemurs, a genus dependent on the forest, to understand how the forests across this island nation changed. One of their research questions asks if the divide between the two forest habitats is natural or what remains of a transitional cline?

Results suggest that the five species studied started diverging from one another roughly five hundred and forty thousand years ago with the last node of divergence around fifty-five thousand years ago. The timing of mouse lemur evolution and divergence coincides with evidence suggesting great variation in climate.

M. murinus. Photo: Joachim S. Muller

Genetic analysis of M. myoxinus, a subspecies of mouse lemur that lives in continuous forests, and M. lehilahytsara, another subspecies that lives in a mosaic of forests, show significantly different patterns in regards to geographic patterns of divergence. Results suggest that M. lehilahytsara, the mouse lemur in a mosaic of forests, has lived in this type of habitat for a very long period of time, since before the arrival of humans. Thus, genetic evidence from mouse lemurs does not support the forest hypothesis.

Yoder and colleagues (2016) also discovered that  M. berthae and M. rufus are more closely related than would be expected, given their geographic differences. One species lives lives in the southeast in humid forests and the other in dry forests of the west. This close genetic relationship points towards the mosaic hypothesis of Madagascar's ancient geography. We see a genetic divergence that is tens of thousands of years old and not uniform across all Microcebus species.

Thus, using the genes of mouse lemurs, Yoder and colleagues (2016) were able to conclude that the central part of Madagascar was composed of a mosaic habitat composed of forests and grasslands. The arrival of humans does not appear to have caused a tremendous change from an entirely forested landscape to grasslands similar to what we see today.


Links of possible interest:

Ecosystems in Madagascar
Read the paper here
They may be cute, but you shouldn't have a primate as a pet


Works cited: 

Blome, M. W., Cohen, A. S., Tryon, C. A., Brooks, A. S., & Russell, J. (2012). The environmental context for the origins of modern human diversity: a synthesis of regional variability in African climate 150,000–30,000 years ago. Journal of Human Evolution, 62(5), 563-592.
Cannon, C. H., Morley, R. J., & Bush, A. B. (2009). The current refugial rainforests of Sundaland are unrepresentative of their biogeographic past and highly vulnerable to disturbance. Proceedings of the National Academy of Sciences, 106(27), 11188-11193.
Scholz, C. A., Cohen, A. S., Johnson, T. C., King, J., Talbot, M. R., & Brown, E. T. (2011). Scientific drilling in the Great Rift Valley: the 2005 Lake Malawi Scientific Drilling Project—an overview of the past 145,000 years of climate variability in Southern Hemisphere East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1), 3-19.
Yoder, A. D., Campbell, C. R., Blanco, M. B., dos Reis, M., Ganzhorn, J. U., Goodman, S. M., ... & Ralison, J. M. (2016). Geogenetic patterns in mouse lemurs (genus Microcebus) reveal the ghosts of Madagascar's forests past. Proceedings of the National Academy of Sciences, 201601081.

Viruses detected on plants chewed by primates

New research has discovered a noninvasive way to test primates for viruses. Collaboration between UC Davis and Gorilla Doctors has shown that the plants mountain gorillas (Gorilla beringei beringei) and golden monkeys (Cercopithecus mitis kandti) consume and discard can be collected and analyzed to determine what viruses the animals have. Blood samples and oral and rectal swabs all require the researcher to anesthetize the animal, something that is not done with critically endangered mountain gorillas unless absolutely necessary.

Thus, this new noninvasive method will allow researchers to detect viruses simply by following the animals at a distance and collecting any bits of chewed bark, leaves, or fruit the individual discards. For this study, Smiley Evans and colleagues (2016) spent almost a year collecting these vegetation discards from 294 gorillas from 26 different family groups across the Volcanoes National Park, Bwindi Impenetrable Forest, and Mgahinga Gorilla Park.

The authors also looked at golden monkeys, collecting plant samples on three different dates in order to determine if their methods could be used on other primate species. Samples were collected from 18 individuals. For both species, researchers observed the animals, collected disregarded plant parts, and sampled from plants with visible bite marks and saliva.

It was possible to collect samples from nearly every individual in a family, including infants who may not consume the plants but still bite and chew them. DNA and RNA viruses were both successfully detected using this method with minimal disruption. Compared to other methods, Smiley Evans and colleagues were able to sample more individuals with less risk and little behavioral disruption. Using this method, the researcher easily knows the age of the sample because close behavioral observation is required.

Golden monkeys proved more challenging than mountain gorillas because they are arboreal and handle food less with their mouths when compared to mountain gorillas. However, it is still possible to collect samples, but researchers should prepare to collect fewer samples per visit.

This research is especially important for mountain gorillas because infectious diseases are one of the greatest threats to this species, and as wildlife increasingly comes into contact with humans, breakthroughs in disease ecology have the potential to positively impact these gentle giants. Roughly 60% of the remaining 880 mountain gorillas are habituated to humans (Gray et al., 2011; Robbins et al., 2011), meaning they encounter humans, whether tourists, researchers, or others, on a regular basis and are accustomed their presence.

Links of possible interest: 

IUCN mountain gorilla page

Gorilla Doctors

Mountain gorilla genome sequenced

Works cited:
Gray, M., Fawcett, K., Basabose, A., et al., (2011). Virunga Massif Mountain Gorilla Census 2010 Summary Report. International Gorilla Conservation Programme.

Robbins, M. M., Roy, J., Kato, R., Kabano, P., Basabose, A., Tibenda, E., ... & Gray, G. (2011). Bwindi Mountain Gorilla Census 2011-Summary of Results. Uganda Wildlife Authority, 28.

Smiley Evans, T., Gilardi, K. V., Barry, P. A., Dsebide, B. J., Kinani, J. F., Nizeyimana, F., ... & Mazet J. A. (2016). Detection of Viruses Using Disregarded Plants from Wild Mountain Gorillas and Golden Monkeys. American Journal of Primatology.