Tuesday, June 30, 2015

Olive baboons can be democratic when it comes to troop movement

Olive baboons (Papio anubis) live in a world where social rank matters. They live in troops that can have over one hundred individuals, with females remaining in their natal group and males dispersing. Males are dominant over females but females have a strict linear dominance hierarchy, meaning who your mother is matters. A lot. Related females groom each other and have each others backs in agonistic meetings.

Photo credit: Nevit Dilmen
A new study out in Science by Strandburg-Peshkin and colleagues shows that, much to everyone's surprise, olive baboons are democratic when it comes to troop movement. Yep, these primates, which can be known for their aggression (just look at those canines), don't bully when it comes to choosing where to go.

What we'd expect in a primate with such a strict social system is that the group would go where dominant individuals want to go. Those lower on the social totem pole aren't going to act against a more dominant individual's decision nor are they going to attempt to make these decisions themselves. However, using GPS technology, researchers found that the troop tends to go where multiple initiators want to go and individuals who move in a directed manner are more likely to be followed.

When two groups within a troop are moving in different directions, the larger group is more likely to win, and this likelihood grows as the difference in size between the two groups of initiators grows. The authors failed to clarify if, of those decisions with multiple initiators, the number of dominant individuals within groups of initiators made a difference. I'd like to know if five low-ranking individuals could top two high-ranking individuals, when determining which direction to go. Does social rank really have no effect? I'm not sure I'm entirely convinced that it doesn't, but I also don't study baboons.

Now, this study was conducted by studying 33 out of 46 members of one baboon troop over nine days, so it'd be interesting to see if results differ in other troops, in troops of differing sizes, or during different times of the year (for example, when food resources are low). It'd also be interesting to see if this finding holds true for other species of baboons. For example, previous research has shown chacma baboons (Papio ursinus) do pay attention to social relations when deciding which patches of food to target (Marshall et al., 2012).

Food for thought:
Strandburg-Peshkin and colleagues didn't find any differences based on sex when it came to an individual initiating troop movement. Why is this surprising?
Why might this system (in which the troop is democratic in deciding where to go) be adaptive to baboons? When might it not be?

Links of potential interest:
Olive baboon behavior and social organization
Chacma baboon study

Literature cited:
Ariana Strandburg-Peshkin, Damien R. Farine, Iain D. Couzin, and Margaret C. Crofoot. Shared decision-making drives collective movement in wild baboons. Science, 19 June 2015 DOI: 10.1126/science.aaa5099

Harry H. Marshall, Alecia J. Carter, Tim Coulson, J. Marcus Rowcliffe, Guy Cowlishaw. Exploring Foraging Decisions in a Social Primate Using Discrete-Choice Models. The American Naturalist, 2012; 180 (4): 481 DOI: 10.1086/667587

Thursday, June 25, 2015

Potential innate difference in tool use between chimps and bonobos

Young chimpanzee. Photo credit Sabine Bresser
Koops, Furuichi and Hashimoto published a paper recently on the innate ability to use tools in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). Both species are our closest living relatives, thus providing opportunities to study the evolution of our species and determine what makes humans human. Tool use has long fascinated biological anthropologists, ever since it was first recorded by Jane Goodall at Gombe in 1960.

The authors tracked both species for three months each and recorded all instances of tool use and all instances they thought had potential for tool usage. Fourteen chimps and sixteen bonobos were studied.

Koops and her colleagues determined the available opportunities to harvest army ants and termites (insects that required tool use), nut trees and stones available below those nut trees (used to crack open the nuts) at each of the two sites. The authors determined that the opportunities for dipping for termites and/or army ants was present at both sites. Opportunities for nut cracking were available but limited.

Bonobo young spent more time with their mothers than did chimpanzees. Bonobos also spent more time in close proximity to each other in feeding contexts. Bonobos also had more individuals in close proximity and more social partners than chimpanzees did, thus bonobos had increased opportunities for social learning. Neither ape cracked nuts. Interestingly, bonobos did not fish for termites or army ants whereas chimpanzees did. Both species were more likely to manipulate objects in a resting context than in a feeding context. The most convincing evidence that there is an innate difference between these two species is that chimpanzees less than one year old were observed manipulating objects. These young animals have had few opportunities for social learning, the authors argue, thus their object manipulation is intrinsic.

I'd like to see this study replicated and expanded. Studying each species for only three months doesn't yield a very large amount of data when we're talking about behavioral studies. The more data the better, and given that chimpanzees and bonobos don't reach maturity until around age eight, it's possible study these young apes for more than a few months. I also think it'd be ideal to see this study replicated across numerous sites, incorporating different habitats. Because neither species cracked nuts, we're really only talking about using tools to fish for ants and termites. Given the diverse tool use we see in animals, I wonder if it is a bit premature to declare that chimps are inherent tool users compared to bonobos given the limits of this study. Nonetheless, Koops and her colleagues certainly made an interesting discovery, and it'll be exciting to see what they discover next, as at least one more publication on this topic appears to be in the works.

For now, chimps have a more innate propensity to use tools for army ants and termites. In the future, we very well may prove chimpanzees have more of an innate propensity for tool use than bonobos or at least a different type of innate ability to use tools.

Links of interest:
Chimps that cook
Female chimps more likely to use tools when hunting
Are bonobos more peaceful than chimps?
How human are chimps?

Literature cited:

Kathelijne Koops, Takeshi Furuichi and Chie Hashimoto. Chimpanzees and bonobos differ in intrinsic motivation for tool use. Scientific Reports, 2015 DOI: 10.1038/srep11356

Wednesday, June 10, 2015

Chimpanzees understanding cooking and choose to do it

We can add another skill to the long list of what chimpanzees are able to do: cook. A study was published last week on a series of cooking related experiments done with semi-free-ranging chimpanzees from the Tchimpounga Chimpanzee Sanctuary and the results are fascinating. This was a very cool series of experiments!

Warneken and Rosati first tested sixteen chimpanzees on whether they would choose to delay and receive a larger portion of food that was either raw or cooked or if they would choose an immediate but smaller portion of food. The chimps chose to wait (and thus consume a larger quantity) 60% and 84.4% of the time for the raw and cooked food respectively, showing that the chimps are more willing to suffer the delay to consume a cooked item than a raw item. This finding isn't surprising, as any zookeeper can tell you apes prefer many cooked foods to raw ones. It gets much better though.

The next experiment tested whether or not the chimpanzees understood cooking. Subjects chose between a container that "cooked" the item and bowl that did not cook the item. Raw food was placed in both the container and the bowl, the experimenter shook both of them, but only the container resulted in cooked food. The chimps chose the container with cooked food over 87% of the time. The next test was to determine whether chimps would immediately consume a piece of available food or place it in either the cooking device or the bowl (that didn't cook the item). Thirteen out of twenty-one chimps chose the cooking device at least one time. Chimps that chose a device chose the cooking device more than 80% of the time. The next experiment gave the chimps carrots, which they had not seen in the context of the cooking devices, and the chimps chose to cook the carrots more often than not. When given non-edible items, the chimps didn't try to cook those. All of these experiments point to chimps having the ability to comprehend cooking on a very basic level. They're not cooking everything and they're choosing to cook items that make sense.

Photo credit: Neil McIntosh
Warneken and Rosati then upped the stakes and placed the cooking device further away to determine if the subjects would travel in order to cook their food. All but one of the thirteen chimps successfully transported food to the cooking device that was far away at least once. And when the cooking device was far away, chimps still chose to visit it 60% of the time.

This study is impressive because the sample size is quite robust for a primate cognition study. (Usually you get sample sizes that are smaller because zoos don't have the ability to house so many animals). Because this study was done with semi-free-ranging chimps at a rehabilitation center, the sample size is larger. We're not talking about one ape that knows some sign language, although that's amazing too. We're talking about roughly thirteen individual chimps that are now probably wondering where that magical container went that cooked all of their food.

Links potentially of interest:
BBC Horizon Video-Did cooking make us human?
How human are chimps?

Literature cited:
Felix Warneken, Alexandra G. Rosati. Cognitive capacities for cooking in chimpanzees. Proceedings of the Royal Society B., June 2015 DOI: 10.1098/rspb.2015.0229

Thursday, June 4, 2015

Rank affects a female's likelihood to seek out "friendships"

Photo: Chris Allen
Chimpanzees (Pan troglodytes) are social creatures, living in a fission-fusion society, meaning one large group often breaks into smaller ones to form feeding parties. In the chimp world, males outrank females and there is a strict linear hierarchy to male relationships (Goldberg & Wrangham 1997). Whereas males can remain in their natal group, females migrate around the time when they reach adolescence (years 9-14) (Nishida et al. 2003). Thus, females eventually need to make new friends, whereas males have the benefit of life-long buddies. In most chimpanzee populations, females spend a lot of time by themselves (Williams, Liu, and Pusey, 2002). At Gombe, the famous site where Jane Goodall first went to the wild and studied chimpanzees, females spend the majority of their time alone or with a few other family members (Wrangham and Smuts, 1980; Goodall, 1986).

Gombe National Park in Tanzania, Google Earth
A study due to be published next month in the journal Animal Behaviour reports new insights into the "friendships" of female chimpanzees. (Friendship may very well be too strong of a word. Acquaintance or association is likely more accurate.) Foerster and colleagues used thirty-eight years of data from Gombe National Park and show that female chimpanzees aren't just bonding randomly with each other. Unsurprisingly, mothers, daughters, and sisters form the strongest bonds. However, among unrelated females, those of a low rank were more likely to seek out other females than were mid or high-ranking females. They also sought out other low-ranking females. 

There are multiple reasons low-ranking females might seek out others of the same rank. As Foerster and colleagues suggest, perhaps having an additional low-ranking pal makes competing for food easier or perhaps they seek others to dissuade higher-ranking members from bullying. The reason for their increased likelihood to seek out other female friends remains unknown at the time. It would be interesting to know how long these partnerships last. If they're temporary, why? What circumstances or events cause the end of the partnership?

 Finally, the presence or absence of offspring affects the likelihood a female will seek out other unrelated females. Females with young female offspring associate with other females less than expected, but females with young male offspring seek each other out. This may because it is especially important for males to interact socially with each other and bond, given that those bonds have the potential to last a life time. The same cannot be said for young female chimpanzees because they will eventually leave and find a new troop. Thus, it apparently is worth forming relationships with other young females within the troop.

Food for thought: What are the benefits and disadvantages to spending time with others (if you're a chimpanzee)?
How might this study differ if the study species had been bonobos? Remember, they have a very different social system!

Links of interest:
ScienceDaily article
Chimpanzee social systems
Chimps create traditions video clip
IUCN Redlist page on chimpanzees
Female chimps more likely to use tools
How human are chimps?

Foerster, S, McLellan, K, Schroepfer-Walker, K, Murray, CM, Krupenye, C, Gilby IC, Pusey, AE. Social bonds in the dispersing sex: partner preferences among adult female chimpanzees. Animal Behaviour, 2015; 105: 139 DOI: 10.1016/j.anbehav.2015.04.012
Goldberg TL, Wrangham RW. 1997. Genetic correlates of social behavior in wild chimpanzees: evidence from mitochondrial DNA. Anim Beh 54: 559-70. 
Goodall J. 1986. The chimpanzees of Gombe. Cambridge (MS): Belknap Pr.
Nishida T, Corp N, Hamai M, Hasegawa T, Hiraiwa-Hasegawa M, Hosaka K, Hunt KD, Itoh N, Kawanaka K, Matsumoto-Oda A, et al. 2003. Demography, female life history and reproductive profiles among the chimpanzees of Mahale. Am J Prim 59(3): 99-121. 

Williams, J. M., Liu, H. & Pusey, A. E. 2002. Costs and benefits of grouping in female chimpanzees at Gombe. In: Behavioral Diversity in Pan. (Ed. by Boesch, C., Hohmann, G., and Marchant, L. F.) pp. 192-203. Cambridge: Cambridge University Press.
Wrangham, R. and Smuts, B.B. (1980). Sex differences in the behavioural ecology of chimpanzees in the Gombe National Park, Tanzania. Journal of Reproduction and Fertility. Supplement, 28, 13-31.