This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
It has been an exceptionally exciting and productive first month for me at the Sikundur research station. I couldn’t have asked for much more in terms of data, and it’s been so hectic that sitting here in Medan, the capital city of North Sumatra, it seems like far longer than a month since I started! I should take this opportunity to point out that my summaries will almost certainly be full of anthropomorphism and speculation, rather than the much more minimalist and technical style of a scientific paper, as I try to explain (and understand for myself) the behavioral intricacies and relationships among orangutans that I’m here to observe. It is a blog after all!
If this were a scientific paper, however, I would probably summarize the month as follows: Over 30 days, I searched for and encountered 13 orangutans, spending a total of 194 hours following seven individuals: one flanged male, one transitional male, one sub-adult male and four females with infants ranging from less than one-month to six-years-old. During this period I recorded 44 “long calls” from the flanged male and collected urine samples from three females and the transitional male. I also completed two days of phenology plots. Aside from the inappropriate use of In (it was a team effort), that all sounds very bland.
Finding an orangutan on my first day in the field was a great start; in the past I’ve gone weeks without collecting any data, so it was nice to get the breakthrough straight off the bat. This first orangutan I followed was Bendot Besar (Big Goat), who’s currently transitioning from unflanged to flanged. This means that although he’s already an adult, he’s only now developing the secondary sexual characteristics of orangutan bimaturism: cheek-pads and a throat sac, which will allow him to produce long calls (the focus of my research). Bendot was a good orangutan to follow, not so afraid of observers that he continuously ran (it gets tiring), but he travelled a decent amount, and had a few interesting social interactions during the time we were following him.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Bendot is currently transitioning into a flanged male, though his cheek-pads are still small.
Because unflanged males like Bendot don’t produce a long call, they cannot attract females for mating from a long distance as their flanged counterparts do. Instead, these smaller males will range widely searching for females to mate with. On the third morning we were following Bendot, he suddenly raced off towards a sound and, as we followed, we heard a volley of kiss squeaks (the noise orangutans make when frightened) and branches crashing (probably because of us, not Bendot). He had encountered Yanti, a female, with her four-year-old, Yeni.
Yeni, 3-years-old, clings to her mother Yanti and eats some fruit.
Orangutan males are larger than females and will often use coercion to obtain matings. This is especially true for unflanged males, who are not preferred as partners by the females. However, as a four-year-old, Yeni was still breast-feeding, thus making her mother unable to conceive another infant. In this scenario it’s expected that Yanti would mate cooperatively with Bendot in order to avoid any cost from his coercive behavior, since she would not incur any penalty in having a “lower quality” offspring. Despite this prediction, during two days spent in a party (less than 50 meters apart) the two had very little interaction, and both seemed very indifferent to one another, to the extent that Yanti even allowed her daughter to play with Bendot at times.
Eventually this indifference got to the point that Bendot stopped following Yanti altogether, and he moved off into another area of the site. Almost immediately he encountered another female, Irma, with her infant, Irwan, a six-year old. After around six years female Sumatran orangutans will begin to cycle again, thus I expected to see her behavior differ from Yanti’s. Interestingly, she seemed much more keen to maintain a party with Bendot, following him rather than the other way around. However, Irwan is still breast-feeding, albeit infrequently, so we’re not sure if she’s cycling yet (I will try ovulation tests next month), and they didn’t copulate in a day-and-a-half together. Again neither individual really approached the other for any direct interactions. Eventually we were forced to abandon the group outside the West of the study area, far from camp, in dense jungle and with few trails to follow. I am very interested in studying Irma more as she begins to cycle again and to see how Bendot matures over the next eight months, during which I hope that he might start experimenting with his long call. Accordingly, these two individuals are likely to be critical animals for my study.
Six days of unsuccessful searching later, during which time a long-calling male continuously taunted me from across the river, we finally encountered another orangutan. It was Irma and Irwan, who’d returned to the center of the grid alone. However, the next day I was scheduled for a day off, so I left them in the charge of Raquel (a grad student from Portugal), Ben and Loga, who unfortunately lost her during a confusing situation when she ran from a new party of three orangutans including Suci (who would become my new focus for a few days), her infant Siboy (three-years-old), and an unflanged sub-adult male, Brutus.
Following these three was a delight, Siboy’s constant desire for play, especially with Brutus, kept us all entertained until we had to abandon them as they left the area. However, the field assistants have since followed the trio, noting a distinct change in the group dynamic, with Suci carrying extensive injuries on her back, and Siboy seeming very subdued. We think potentially Brutus tried to mate with Suci, who resisted, leading to a fight in which Siboy could easily have been hit as he attempted to cling to his mother and perhaps even to intervene. It will be interesting to follow them again and to try to figure out exactly what happened.
Brutus is an unflanged male, who has recently been observed producing the “lork” call.
In the middle of the month we hit another lull, with a few days of unsuccessful searching until one morning, in the east of the site, we found a new unflanged male, Anto, and a very small, adolescent male, Kundur, who’d only been followed once before. They did not seem pleased to see us, kiss squeaking and throwing large branches before setting off at a furious pace across the jungle.
Kundur is an adolescent male who has probably only recently left his mother to live on his own, since he is very small.
We ran behind them for a while, eventually catching up when they stopped to feed in a jackfruit tree, where, after a brief argument about where the orangutans were, we realized there was in fact a third orangutan present, Madelena. And, in an even bigger shock, she was carrying a new baby, less than a month old! I followed her for five nice days. She’s very well habituated, didn’t seem to mind socializing with Anto, and best of all, often comes close to observers, which gave us a great opportunity to see the new infant, who is far younger than any orangutan any of us had seen before, and whom she often carries around her neck! I collected some urine samples, and it will be interesting to see how her hormones reflect the new birth, along with her urinalysis results which, unsurprisingly, showed high leucocyte levels and some ketones, indicating her fat stores are burning up. Interestingly, and consistent with other Sumatran sites, all my other individuals so far have not been producing ketones, indicating they’re not energetically stressed, though I’m interested to see how this changes with fruit abundance in what is a far lower productivity site than Suaq or Ketembe, where most Sumatran research has been conducted.
Madelena inspects her newborn baby, while Anto (right) watches her.
Needing a break from following the orangutans (it gets tiring, and with her newborn, Madelena slept a lot, which isn’t the most exciting experience), I took a couple days off to do some phenology transects with Suprayudi before this last week, which has definitely been one of the best of my short career so far!
It started with another attempt to follow Brutus, who our field assistants reported producing a rare “lork call” which seems like it could be an unflanged male’s version of the long call! Sadly, despite me and Raquel following him with mics and recorders rolling, he didn’t produce! This was perhaps because he’d encountered Yanti earlier in the day and had formed yet another party. The two of them followed one another around all day, frustratingly making nest after nest, but never being able to rest, since the other was awake, which resulted in them taking us way out to the east of the study area in a massive travel day. To add insult to injury, they didn’t even make night nests until after it was far to dark for us to see, so we had to abandon them without getting a full follow day.
Frustrated, I put in another day with Madelena, which was again fairly uneventful, but adds nicely to my behavioral data set (and the baby is adorable), before we started searching again the following day. Our previous searches were done in groups due to my not being trustworthy enough, but three weeks in Suprayudi gave me permission to have a search alone, which was nice, but didn’t work that well, since Supri found an orangutan at 10am, but, due to the vagaries of Telkomsel’s cellular network (I did have signal), he couldn’t get hold of me until well after midday. It was Yanti and Yeni, who’d returned to the grid, and despite the former’s constant protests (kiss squeaks all afternoon), we managed to keep them until the end of the day as she made a bee-line towards a long-calling, but distant (and slightly out-of-area) male, a potential key animal for my study.
Returning to camp that night, I was frustrated that we were so close to one of the males I need to study, yet we weren’t “allowed” to track him down because he was outside of the study area. We estimated Yanti’s nest was only around 800 meters away from his final long call made at 5:12pm, but her nest was also right on the border of the national park. We had a chat about the situation, deciding that we’d try going around the outside of the park through some orange groves in order to find the male, even if we could follow him only for a few hours given the long distance to camp. Accordingly, the next day we found ourselves hiking through the farmlands, sweating copiously under the unforgiving sun, since orange trees offer little shelter! To increase our chances of finding the male Supri decided to ask the farmers, which turned out to be a masterstroke since they pointed us in the direction of the three long calls he’d already produced that morning, and gave us some delicious oranges (great for morale). Following their instructions, we turned in to the jungle and within 20 minutes had found a brand new flanged-male lounging in a tree. Within another five minutes I had recorded my first long call in Sumatra!
James is one of three flanged-males who have been spotted at Sikundur over the past 18 months.
The male has since been named named James, after me (camp manager’s decision, honest!). He’s big, but by no mean the largest male at the site, though he might be a candidate for the dominant, since his multiple broken fingers and toes suggest he fights a fair amount, and his frequent long-calling suggesting he wins (or thinks he’ll win) a decent amount too! Despite our deal the night before, there was no way I could give up a flanged male, especially since James was producing long call after long call throughout the day, giving my data collection a massive early boost! So, following a brief text-message based argument, it was agreed we’d keep him until the end of the day, and, as luck would have it, James travelled towards the eastern edge of the study grid, allowing us to follow him the next day without the need for further negotiation!
On the first day I recorded 15 long calls from a number of different contexts; on the second day it was 23; and on the third, truncated day another six. This is an insane amount of long calls – more than I collected from three separate males over four months during my master’s research! James’ long calling ability is much more impressive than any male I’ve encountered previously, not only in terms of quantity, but also duration, with his calls regularly lasting over five minutes and on one occasion, late on day two, he produced an epic call, which lasted over 10 minutes. It’s going to be interesting teasing out why exactly he calls so frequently. Certainly, although he wasn’t too concerned by our presence, kiss squeaking infrequently, we do think following him for the first time probably had an effect, since some of the long calls were directly aimed at us, and at one point he even produced a “fast long call” a very-rare vocalization that sounds like a speeded-up long call, and which is only produced by highly disturbed individuals (he’d just been kiss-squeaking at us when a large animal ran past in the bushes and he freaked).
Another factor that also may have contributed to his high volume of long calls was an encounter with an extremely unfortunate unflanged male, Anto (whom we’d met earlier in the month), towards whom James unleashed a very aggressive long call, which included the violent dismantling of a tree. Anto ran away, and James called frequently for the rest of the day. This whole incident is incredibly interesting, since previous studies have found male long call production generates a protective sphere into which unflanged males will not enter. Yet, despite James having called fairly regularly throughout the day, including just 15 minutes before, an unflanged male appeared within 30 meters of him. The best rationale we have for this is that Anto was trying to intercept any females attracted to James’ long call and simply got the distance wrong. Clearly, further work is needed, and it would be great to simultaneously follow a flanged and unflanged male pair to see how the unflanged male responds to the long calls, and how their spacing changes accordingly.
Ideally, I would like to have followed James for the maximum 10 days, but despite the entire second day being spent in the grid, he gradually drifted further and further north, right out to the edge, leaving us with an epic hike back to camp on day two and, of course, the same to return on day three (I know it’s a bad distance when the field assistants trade who’s following with me from day-to-day). Once again deals were made. Ben and me would follow as long as we could (officially it’s 200 meters outside the grid, but it’s all trail dependent really, and as long as there are trails, the guys are generally happy to follow anywhere), in the hope that James would turn back south at some point. He did not, instead dragging us northward once again. As the trails disappeared and the vegetation grew thicker and spikier, we contemplated the possibility of abandoning James. However, before we got to that point, he made the decision for us.
First he chased us a little, which is fairly common with big males, and not really dangerous. When being chased by a wild orangutan the key thing is to behave like a submissive ape – that is, get down on the floor, eat leaves and don’t make eye contact. They will stop charging, possibly stare at you for a bit, and then move on to find some food (note: this works with wild animals only, and is not a viable strategy when being chased by a captive or rehab animal used to touching humans). Next, he decided he wanted to eat honey. Orangutans going after honey is a nightmare for observers; they have thick skin so will sit next to a nest, breaking it to bits, and dipping their hands into the sweet goo without suffering the consequences. Meanwhile the bees will, unsurprisingly, go berserk, stinging anyone within the area. After Ben got stung in the face a couple of times, we ran about 20 meters up the hill, leaving us with a very limited view of the orangutan, as he happily destroyed the nest.
After a little while, James dropped a large chunk of the nest to the ground, forcing us even further away. Seemingly satiated, rather than climbing back into the trees, he drifted off into the undergrowth on his wrists and feet. On the jungle floor, orangutans are difficult to follow (doubly so if there’s also a swarm of angry bees), making almost no noise and leaving barely any movement of the undergrowth to track. Thus we found ourselves alone in the forest. My gut feeling is we could have found him again if we’d really wanted to (possibly this is just pride talking), but since we were already a kilometer out of the grid, we would’ve abandoned him soon anyway, so we decided to trek back to camp.
It was an inauspicious end to my first month’s research, but I’m utterly delighted to have recorded so many calls and followed so many individuals in such a short time. And, I’m very excited to follow James in the future, and to see how his long calls work out in the playback experiments I’ll starting in the second month.