Drawing on a 15-year study of wild orangutans, researchers used the focal-follow method, tracking the same mother-infant pairs from dawn to dusk and logging behavior every two minutes plus GPS fixes every 30 minutes, to see whether mothers deliberately arrange play encounters for their infants. Across roughly 32,600 observation hours and 31 mother-infant pairs, play was rare (about 6.3% of days) but showed a strong exponential drop-off as the age gap between playmates grew, and mothers' foraging ranges overlapped more with other mothers who had similarly aged infants than with relatives, pointing to intentional matchmaking rather than just family proximity. On days when infants played, mothers also traveled about 20% farther and spent less time feeding, showing the behavior carries a real energetic cost.
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The focal-follow technique used here is the same observational method famously associated with Jane Goodall's chimpanzee studies.
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The dataset included over 3,000 follow-days, with about 2,000 being complete nest-to-nest days.
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Controlling for how often pairs met, relatedness did not increase per-encounter play rates, suggesting kinship explains proximity but not playfulness itself.
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Fruit availability had little effect on play rates once other factors were accounted for, ruling it out as a major driver of these meetups.
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15:18>> they're having a great time. And one of the things that the first author Van Nordwick noticed is that these infant encounters, >> they seem to come at a cost to the mothers. >> Oh, okay. >> Okay. The cost being it's a really long and hard day for them >> when they have to arrange these playdates. >> Are they even arranging these playdates? And if they arrange these playdates, >> are they doing it at an expense to their own benefit? Right? Cuz they could be doing other things. >> Resource gathering. >> Yeah. They could be eating. They could be resting. Instead, they're doing this, right? So, is it a concerted effort? After 15 years, they've amassed 32,000 hours of observation from 31 mother
16:00infant pairs. That's actually incredible. First of all, right? >> Like 15 years of work, 31,000 hours. >> That's like on the order of like a year a year of just like continuous observing orangutans. It's incredible. The basic technique is something called a focal follow. This is a very famous photo of Jane Goodall >> doing a focal follow on chimpanzees. >> The idea is that you have researchers that choose an identified individual and then you basically follow its behavior from sundown to sunset or from sunrise to sunset. >> Um you monitor every 2 minutes
16:41where the person is. So you have like a GPS monitor and you're like, "Okay, I'm going to monitor where the orangutang is right now. I'm going to monitor what the animal is doing at that moment. So is the mother feeding? Is the youngster playing with whom? And roughly every 30 minutes you log a GPS location, right? So you you get a kind of GPS of of where this person where where this animal is going and you get uh every two minutes some kind of log of the activity. Mhm. >> over the entire day. >> That's a quite that's a a rich data set. >> Yeah. Incredible, right? And and it requires a human being just straight up following this orangutang or this mother
17:24infant pair for the entire day. >> Mhm. >> Pretty incredible. >> For days and days and days and it's the same individual that you have to follow for days and days because you want to have some type of longitudinal data on the same individual. >> Yeah. >> Now, the data set here includes 3,000 plus follow days, 2,000 of which were full nest to nest days, meaning like like there's like mothers and all. Um, only 6.3% So only 6% >> did they record play. >> That's that's incredible. What we're saying is over the course of all this observation, a less than 10% proportion of it has this peer play concept, has
18:04the the thing we're looking for. And that's why you need such a large data set because it's so infrequent. >> Yeah. And you need a large data set because if you have infrequent events >> in order to do good statistics, you need a large data set, right? >> Reminds me of the ice cube nutrino detector. >> 100%. It's the same thing. It's the same exact paradigm, right? Cuz you need a lot of events in order to hone down on a very rare like per chance. >> Mhm. >> So now let's get into the figures. They've collected all this data. What do they actually see? Let's start actually with figure C here. This is figure 1. In C on the x-axis, you have the age
18:45difference between two offspring that are meeting up for a play date. And meeting up meaning, you know, they're playing with one another. This is obvious from a human that's like looking up and seeing them. >> Um, on the Y ais is their play rate, which is, you know, some normalized sense of how often do these two individuals get together. >> Wait. Oh, so we're looking at C. >> Okay. Yes. >> Right. We're looking at this this part right here. >> And there you can see there's a negative correlation meaning >> that as the age difference gets bigger, the play rate diminishes. >> Yeah, that makes sense. >> Kind of makes sense, right? >> My little brother and I have a 13-year age gap. >> Yeah. >> So, our play rate was much lower than siblings who were much closer together.
19:26>> Exactly. The other cool thing is on the y-axis, it's actually exponential. That's a log scale cuz it goes like 10 -1, 10 - 2, 10us 3. So this is exponential decay. It's a very strong effect that you're seeing which is like it seems that like the the closer you are to age the longer you're going to play like right okay on A and B what we're actually seeing is the effect size based on different markers that the the human beings that are on the ground are actually like marking. For example, you can track the relatedness of two individuals and you can track the fruit availability in the in the forest
20:08because you could imagine, right, fruit availability is a compound. If there's a lot of fruit, then of course the mothers are going to be foraging a lot and so they're going to meet up a lot, >> right? You want to disentangle those and see what's the actual effect. Well, actually fruit availability is not that is not that high. In effect, the correlation is not that big. On the other hand, >> related relatedness, like whether you're related to the other kid, >> that's high for occurrence. But if you control for occurrence, the amount of play that you do per occurrence is not that high. >> That if you if if you're family, I'm not about that life.
20:48>> Yeah. Like like we'll meet up a lot. >> Yeah. Yeah. But >> but I would I would play with you just as much as I would play with a friend. >> You see what I'm saying? >> Yeah. Yep. Yep. >> Like there's a difference here. Like maybe the occurrence is higher with family because like the moms know each other. >> But just because you're family doesn't mean I play with you more. >> Yeah. Yeah. I play with you the same amount that I would with like a stranger's kid, right? Um the two big anti-correlations are again age difference. That's the very top. Mhm. >> It's like if the age difference is very high, then the amount of play rate is very low and the occurrence is very low. So, it seems to be that the mothers have honed in on who has the offspring that
21:28is about the same age as my kid. >> Fascinating. >> Isn't that crazy? >> That's so good. >> Like, I mean, they're keeping track. >> Yeah. Yeah. Yeah. >> Of like of like who has the the right age group >> of kid. Now, the the other cool thing, the ranges overlap for moms because I told you, right? The the the moms have a um they're solitary, which means that the range of forest that they forage might not overlap all that much, but overlap is higher for moms that have similar age group, kids. >> Oh, that's really good. >> Right. >> That's really good. >> Because you have this data over 15
22:08years, you've been collecting GPS data. Yeah, >> you can actually tell where the moms forage and the overlap is higher. It's stronger for two moms that have similar aged kids, >> which is pointing to this idea of some intentionality of going to that place of overlap because I know the p the other mom that comes around here, >> their little their little Bobby and my little Timmy are about the same age. >> About the same age, right? So, they can they can like play around. This this entire paper is going into that intentionality, right? Can we prove intentionality in orangutang mothers? That's the point. >> And the way they've structured these questions and the data points they're
22:50tracking in order to reach this this >> the conclusions about intentionality >> are very clever in the areas that they're trying to cover to remove other confounding variables. >> Exactly. Yeah. And that's it. I've always find this fascinating because like especially with anal behavior, it's very hard to think of all the compounds, but these guys are doing a pretty good job. I think >> that's quite nice. >> Um the next figure is figure two. Here we talk about um what it costs for the mothers, right? Um here the researchers are comparing three different categories. There's days when the mother was alone with her offspring. There's days when another orangutang is nearby,
23:31but there's no play. And then there's days when there is infant play. Okay, those are the three sort of categories. Um the middle category is really important because here we're simply disentangling between like okay if another orangutang is nearby does that have an effect versus another orangutang is nearby and my infant is playing right there's there's two different things that are happening and here we're seeing an actual difference right on the left hand side this is the daily amount of path that the mother takes when the kid is playing the path length that the other traversed in the forest is a lot longer. >> Yeah.
24:11>> Almost 20% longer. >> Yeah. >> Okay. Which means that she's she's exerting more effort to actually go from one place to another. >> On the right hand side, figure 2C, that is the proportion of time feeding. >> This is what's most important to me and most salient to me. The amount of time that the mother spent feeding herself was lower on days when her infant played with another friend. There there's there's more caloric deficit from the amount of movement >> while having a lower amount of caloric intake at that stage when you're having this higher caloric deficit. >> Yeah. Yeah. Yeah. It's it's a twof it's
24:53a twofold >> Yeah. >> effect. >> Yeah. And and you know as human beings part of this is going to feel like be like oh obviously like we talk about child care and >> all these things and you are experiencing this personally right now and and going through that. >> Yes. Okay. With human beings for sure. >> Yeah. >> But we're trying to empirically show this
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