MONKEYING AROUND: COMPARING PLAY BEHAVIOR IN RELATION TO PREDATION RISK IN SYMPATRIC OLIVE BABOONS (PAPIO ANUBIS) AND VERVET MONKEYS (CHLOROCEBUS PYGERYTHRUS)

Danielle Steinberg

Abstract:

Predation has long been considered a strong selective pressure on primate behavior, including foraging and feeding. However, its effects on play behavior, a crucial aspect of primate life, are unknown. Feeding is necessary for survival, but play is imperative for later reproductive success. Olive baboons (Papio anubis) and vervet monkeys (Chlorocebus pygerythrus) are often sympatric but baboons are larger and more aggressive, suggesting that they may be less vulnerable to predation and thus may have longer or more frequent play bouts. Similarly, within species, male primates, being more aggressive than female primates, may be less vulnerable to predation and so may play more than females. I observed play behavior of baboons and vervets in Nyungwe and Akagera National Parks, Rwanda, to test these predictions. I used all-occurrence sampling to record frequencies and durations of play bouts and analyzed the data with nonparametric statistical tests. There were significant differences in play bout frequencies but not durations both between the species and between males and females within species. Future research should explore whether life history differences also contribute to differences in play behavior.

Keywords: Vervet | olive baboon | play | predation

Introduction the habitats proportionally to their availability and they spent less time in food-rich areas Primates and their predators have been in an than expected due to the higher risk of evolutionary arms race for over 70 million predation in those areas. In a similar study, years (Isbell, 2009). The effects of predation Coleman and Hill (2014) found that samango as a strong selective pressure on primate monkeys (Cercopithecus mitis erythrarchus) behavior have been studied in numerous decide on habitat usage based on predation contexts. Ecological tradeoffs lie at the root of risk rather than on resource availability. predation as a selective pressure, specifically in Ultimately, predation may lead to trade-offs in regards to feeding and foraging behaviors and foraging, habitat use, or another common habitat use (Cowlishaw 1997; Lima 1998; Hart behaviors in primates (Lima 1998; Hart 2007). 2007; Coleman and Hill 2013). For instance, Though predation has obvious effects in a study conducted by Cowlishaw (1997), on the daily lives of all primates, certain chacma baboons (Papio ursinus) were characteristics may make some primates more observed under different conditions of prone to predation than others. Smaller- predation risk and food availability in a given bodied primates are more susceptible to habitat. He found that the baboons did not use predator attacks than are larger-bodied

© D. L. Steinberg 2017. Originally published in Explorations: The UC Davis Undergraduate Research Journal, Vol. 19 (2017). http://Explorations.UCDavis.edu © The Regents of the University of California. primates (Isbell 1994; Enstam 2007). For this widespread theory on the functionality of play reason, different primate species tend to have is honing social skills that can be utilized different predator avoidance or deterrent throughout the animal’s life (Chalmers 1987; strategies. Shultz et al. (2004) noticed that Lewis 2000; Fairbanks 1993). Play often terrestrial primates are more likely to live in necessitates cooperation and communication large groups or to be large in body size as a between partners which inherently works to predator deterrence strategy. One hypothesis increase social competency. Lewis (2000) regarding extreme sexual dimorphism in some noted that primate social play was positively species is that large males act as predator correlated with neocortex ratio. She attributed deterrents, implying that large body size does, this to the fact that social play requires a in fact, reduce risk of predation (Leutenegger number of complex cognitive function such as and Kelly 1977). In addition to large body size, predicting behaviors and reacting alarm calls are another popular predator appropriately which, in turn, helps the animals deterrent (Enstam 2007; Isbell and Bidner develop skills useful in their adult lives. 2016). In a study by Enstam and Isbell (2002), Fairbanks (1993) noted that even the motor predation responses were compared between skills acquired through play can aid in primate vervet monkeys (Chlorocebus pygerythrus) reproductive success. She argues that male and their slightly larger relatives, patas primates develop fighting skills through play monkeys (Erythrocebus patas). They found and that fighting ability in male that vervet monkeys tend to alarm call and flee cercopithecines often precipitates greater while the larger, more aggressive patas reproductive success. Social competency is monkeys would sometimes engage in “active even more crucial to reproductive success defense” (Isbell and Enstam 2002). Like patas because successfully integrating into a new monkeys, red colobus (Piliocolobus group post-dispersal requires appropriate tephrosceles) males have also been observed to social skills (Platt et al. 2016). Ultimately, use aggression as a predator deterrent playing during the juvenile period helps build (Struhsaker and Leakey 1990; Boesch 1994; the skills necessary for later acceptance in Mitani and Watts 1999). In three separate future social circumstances including dispersal studies, researchers noticed that chimpanzees and, later, courting behavior. attacked younger red colobus and avoided Even though play eventually produces adult males due to their aggressive responses benefits, there are immediate costs. Play is a (Struhsaker Leakey 1990; Boesch 1994; Mitani very risky behavior because it puts individuals Watts 1999). in precarious situations and leaves them Just as all primates are subject to susceptible to predation (Struhsaker and predation risk, all primates play. Play is Leakey 1990; Lima 1998; Fagen 1993). During defined by Burghardt (2005) as satisfying play, individuals are not completely aware of several conditions including arising their surroundings and are prone to falls. A spontaneously, having no immediate function, number of studies involving lethal falls cited by and occurring in a stable environment. While Fagen (1993) indicate the high risk that often many primatologists agree that the benefits of correlates with play. Furthermore, play play occur much later than when the act itself reduces the capacity for vigilance as attention takes place, the specific benefits are still is directed toward the object of play rather debated (Chalmers 1987; Pellis 1988; than surroundings. For instance, in a study of Struhsaker and Leakey 1990; Lima 1998; yellow baboon (P. cynocephalus) predatory Lewis 2000; Fagen 1993; Fairbanks 1993; behaviors, Hausfater (1976) noted that the Maestripieri and Ross 2004). Developing baboons preyed upon mostly younger vervets good motor skills is one of the primary who were in play groups away from the more hypothesized functions of play (Fagen 1993; vigilant adults. In addition to reducing Maestripieri and Ross 2004). A second vigilance, play makes individuals more UC Davis | EXPLORATIONS: THE UC DAVIS UNDERGRADUATE RESEARCH JOURNAL Vol. 19 (2017) Steinberg p.2 conspicuous to their predators. In its most previously, both body size and aggression have simple yet justifiable form, increasing activity been shown to be negatively correlated with leads to an increased risk of predation (Lima predation risk so baboons should therefore 1998). Struhsaker and Leakey (1990) found have a lower risk of predation than vervet that crowned hawk-eagles (Stephanoaetus monkeys do in the same general environment. coronatus) did not randomly select primate Here I test the prediction that risk of prey, but rather targeted adult males in four predation affects olive baboon and vervet primate species (except red colobus as noted monkey play behavior differently. Specifically, above) because they tended to be more I predicted that baboons would have both demonstrative, give more alarm calls, and be longer and more frequent play bouts compared less cautious overall which made them very to vervets due to lower risk of predation conspicuous, easy targets. Similarly, play because of their larger body sizes and more reduces vigilance and increases noticeability aggressive nature. To examine the relationship making the players easy targets for predation. between predation risk and body size and Evolutionarily speaking, risky behaviors aggressiveness further, I also predicted that should not be performed unless they have female baboons would play more often or for benefits that outweigh the costs. This longer than female vervets, male baboons necessitates then that play does in fact lead to would play more often or for longer than male benefits such as those stated above in order for vervets, and within each species, males would the tradeoff to be worth it evolutionarily. play more often or for longer than females. While play involves risk of predation, the risks themselves vary across species and habitats (Enstam 2007). In order to account Methods for these variables, I selected vervet monkeys and olive baboons, two species very similar in Study sites habitat and that share common predators, to I collected data from June 14 to June examine how predation may affect play 30, 2016 in two of Rwanda’s national parks: behavior. Vervets and olive baboons both Akagera National Park (1.60° S, 30.72° E) and share leopards (Panthera pardus) as a Nyungwe Forest National Park (2.53° S, 29.28° common predator and are both found in East E). Akagera is situated in a warm, dry savanna Africa, in places such as Rwanda where I and Nyungwe is a mountain rainforest. In observed them. While these two species may Akagera, I observed both lodge groups live in the same areas and share a common (situated next to a hotel) and groups located predator, they differ quite obviously in other away from constant human habitation. The respects. Body size is the first evident only group in which play was observed in difference between these two species. On Nyungwe was also situated next to a small average, olive baboons are approximately five hotel. times the size (weight) of vervets (Dechow Study subjects 1983; Isbell and Jaffe 2013). Olive baboons The two species I observed for this are also much more aggressive toward study were olive baboons and vervet monkeys. predators than vervet monkeys; vervets are Another researcher and I recorded data from known for their species-specific alarm calls several baboon troops; group sizes ranged while baboons tend to actively defend and even from five non-adults to thirteen non-adults attack during times of predation (Cowlishaw (adults were not counted in demographics due 1994; Enstam 2007; Isbell and Bidner 2016). to the challenge of counting large groups in a In fact, Cowlishaw (1994) found that in four of short period of time). The only vervet group in the eleven documented instances of baboon which play was observed consisted of two adult retaliation against leopards, the primates males, two adult females, four subadult actually killed the felid. As mentioned females, two juvenile females, one infant male, UC Davis | EXPLORATIONS: THE UC DAVIS UNDERGRADUATE RESEARCH JOURNAL Vol. 19 (2017) Steinberg p.3 and one infant female. All of the groups predators (Mann-Whitney U test: UA = 2428, observed were semi-habituated. P(1) = 0.42, 1-tailed; Figure 1). Data collection and analysis Female baboons vs female vervets My data collection partner and I first I observed 40 individual play bouts by tested our inter-observer reliability in female baboons and 34 play bouts by female identifying age-sex classes of individuals by vervets. Female baboon play bout durations comparing our observed demographics and ranged from 5-73 seconds with an average of defining age class based on visual observation. 23.7 seconds while female vervet play bout We collected observational data on play using durations ranged from 5-51 seconds with an all-occurrences sampling. Upon arrival at a average of 24.9 seconds. Female baboons did study site, we would collect demographics of not play significantly longer than female the group and then immediately watch for play vervets (Mann-Whitney U test: UA = 740.5, P(1) behavior. Whenever play was observed, we = 0.26, 1-tailed; Figure 2). recorded the sex and age class of the player(s) Male baboons vs. male vervets and the duration of the play bout. If group I recorded 84 individual play bouts for composition changed during the study period male baboons and six individual play bouts for in the area of observation, we collected male vervets. The duration of play bouts for demographics again and continued observing male baboons ranged from 5-145 seconds with play. We compared our data regularly to an average of 32.7 seconds while the duration ensure accuracy and consistency of data of play bouts for male vervets ranged from 6- collection. 44 seconds with an average of 26.5 seconds. We observed the animals for 421 Male baboons also did not play significantly minutes which included approximately 78 longer than male vervets (Mann-Whitney U minutes of play (play made up 18.6% of the test: UA = 252.5, P(1) = 0.5, 1-tailed; Figure 3). total observation time). In total, 164 separate Male vs. female baboons play bouts were recorded, 124 play bouts for I recorded 84 individual play bouts for baboons and 40 play bouts for vervets. male baboons and 40 for female baboons. The I used Mann-Whitney U tests to analyze duration of play bouts for males ranged from the data for play bout durations and Chi- 5-145 seconds with an average of 32.7 seconds square Goodness-of-Fit tests to analyze the while the duration of play bouts for females data for frequencies of play bouts. In total, I ranged from 5-73 seconds with an average of tested for differences in play bout duration and 23.7 seconds. These data indicate that male frequency between baboons and vervets, male baboons played significantly longer than and female baboons, male and female vervets, female baboons (Mann-Whitney U test: UA = male baboons and male vervets, and female 1337, P(1) = 0.03, 1-tailed; Figure 4). baboons and female vervets. Male vs. female vervets I recorded six individual play bouts for male vervets and 34 for female vervets. The Results duration of play bouts for male vervets ranged from 6-44 seconds with an average of 26.5 Duration of play bouts seconds while female vervet play bout Baboons vs. vervets durations ranged from 5-51 seconds with an Baboon play bout durations ranged average of 24.9 seconds. Male vervets did not from 5-145 seconds and averaged 29.8 play significantly longer than female vervets seconds. Vervet play bout durations ranged (Mann-Whitney U test: UA= 105, P(1) = 0.46, 1- from 5-51 seconds and averaged 25.1 seconds. tailed; Figure 5). Baboons did not play for significantly longer Frequency of play bouts periods than vervets did despite their larger Baboons vs. vervets body size and increased aggression towards I recorded 124 play bouts for baboons in UC Davis | EXPLORATIONS: THE UC DAVIS UNDERGRADUATE RESEARCH JOURNAL Vol. 19 (2017) Steinberg p.4 the 285 minutes spent observing them and 40 than females. Despite being larger-bodied and bouts for vervets in the 136 minutes observing more aggressive, baboons may not have played them. According to these data, baboons played longer than vervets simply due to lack of significantly more frequently than vervets motivation. In other words the animals may (Chi-square Goodness of Fit test: χ2= 45.06, p just stop playing after a 30 second bout, for < 0.0001; Figure 6). instance, because they have lost interest in the Female baboons vs. female vervets object of play or other player. Of the 124 baboon play bouts, 40 were In contrast to duration of play bouts, from females. Of the 40 vervet play bouts, 34 frequencies of play bouts were significantly were due to females. Once total observation different across all comparison groups. time was accounted for, the data show that Baboons played significantly more than female vervets played significantly more vervets overall, female vervets played more frequently than female baboons (Chi-square than female baboons, male baboons played Goodness of Fit test: χ2= 50.88, p < 0.0001; more than male vervets, male baboons played Figure 7). more than female baboons, and female vervets Male baboons vs. male vervets played more than male vervets. These data do I recorded 84 play bouts from male not seem consistent with each other in the baboons and six from male vervets. Taking context of my hypotheses, but sample size is total observation time into account, male probably to blame. Based on my hypotheses, I baboons played significantly more frequently expected males to play more than females due than male vervets (Chi-square Goodness of Fit to their larger body sizes and baboons to play test: χ2= 306.3, p < 0.0001; Figure 8). more than vervets across all categories due to Male vs. female baboons both larger body size and greater aggression. I observed 84 play bouts from male The data are not consistent with this in the baboons and 40 from female baboons in the female baboons vs. female vervets and male same total observation time. These data show vervets vs. female vervets comparisons. I that male baboons played significantly more believe that this is the case because the vervet frequently than female baboons (Chi-square group that played was very small and consisted Goodness of Fit test: χ2= 90.4, p < 0.0001; of far more females than males (seven non- Figure 9). adult females, one non-adult male) so data will Male vs. female vervets skew accordingly. I recorded six play bouts from male Alternative explanations for the vervets and 34 from female vervets in the same differences in play frequency between baboons overall observation time. These data show that and vervets include diet, group size, and group female vervets played significantly more than locations. Perhaps diet affected play behavior male vervets (Chi-square Goodness of Fit test: because energy is needed for play and different χ2= 238.22, p < 0.0001; Figure 10). diets lead to varying amounts of energy. There were baboon troops that I observed both by a Discussion consistently human-inhabited lodge and troops that lived much further from constant Contrary to what I predicted, I found no human activity. The lodge groups often stayed significant differences in play bout duration on and around a large trash heap in which they between olive baboons and vervet monkeys. In often foraged through and ate from thereby fact, there were no significant differences in consuming a lot of discarded scraps from durations of play bout between any of the human foods. Similarly, for vervets, the only categories compared (e.g. male baboons vs. group in which I observed play behavior was male vervets, male vervets vs. female vervets, one that lived by a small hotel. While I was etc.) except between male and female baboons collecting data, one of the hotel staff threw a in which the males played significantly longer small banana at the monkeys to keep them out UC Davis | EXPLORATIONS: THE UC DAVIS UNDERGRADUATE RESEARCH JOURNAL Vol. 19 (2017) Steinberg p.5 of the hotel itself though some managed to get predation, at least by leopards, than the other in and steal more fruit which implies that the groups simply due to close human proximity group is often provisioned. Furthermore, the and so do not have to be as vigilant. other groups of vervets in Akagera were far In the future, I would like to test these from human habitation and, therefore and other alternative explanations for the provisioning, and did not play at all during the results I obtained. First, the “group size effect” time I spent observing them. The fact that the could be tested by controlling for group size by both the baboon and vervet groups that were observing groups of baboons and vervets of the subject to human provisioning (intentional or same size and seeing if there were still any not) played more than the non-provisioned significant differences in play. If the group size groups leads credence to this idea, though effect was the true independent variable in more empirical data collection on this subject play bout frequencies, I would expect no would need to be collected. In a similar study, significant differences between baboons and Kamal et al. (1997) observed that play behavior vervets in equal sized groups. Furthermore, I increased in juvenile hamadryas baboons (P. could control for species as well and observe hamadryas) when they were provisioned different sized groups of baboons and, compared to when they naturally foraged. separately, observe different sized groups of A second alternative hypothesis is due vervets. If play frequencies were positively to the “group size effect” as explained by Lima correlated with group size, I could not reject (1998). In essence, the idea is that individuals this hypothesis. in larger groups are not required to be as For the proximity to humans vigilant as individuals in smaller groups simply hypothesis, I could look solely at baboons in because there are more eyes and ears available Akagera and take more specific data on the to detect predators. Because vigilance per differences in play between the lodge groups individual does not have to be as high, more and non-lodge groups. If the lodge groups time is available for behaviors that interfere played significantly more than the other with vigilance such as play. Baboon troops are groups, I could not reject this hypothesis. generally larger than vervet groups so vigilance Ultimately, there is a difference in play per individual should theoretically be less in bout frequencies between the species, yet the baboons than it is in vervets. This concept was exact mechanism for why this difference exists shown to be true for vervets in Amboseli remains unknown. There are many potential National Park in Kenya where various groups explanations for this correlation, but future of different sizes were observed and their studies must be done in order to come to a activity budgets recorded (Isbell and Young clearer conclusion. 1993a). Isbell and Young found that larger groups of vervets had more overall scanning, yet fewer instances per individual compared to Acknowledgements the smaller groups. The third alternative explanation for the I would like to thank Dr. Netzin and Dr. differences in play bout frequencies relates to Dieter Steklis of University of Arizona for human proximity. As noted above, the lodge organizing the trip to Rwanda and teaching groups of both baboons and vervets appeared me so much throughout the process. I would to play more than those groups further away also like to thank Jack Winans for collecting from human-inhabited areas. Isbell and the data for this project with me. Most of all, I Young (1993b) found that predation risk was would like to thank Dr. Lynne Isbell for reduced for vervets in closer proximity to walking me through every step of this process humans and they suggested it was due to and guiding me on this journey as well as for avoidance of humans by leopards. Perhaps the continuing to support and inspire me day lodge groups have a much smaller risk of after day. 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Baboons, Papio hamadryas, at Al Hada Shultz, S., Noe, R., Mcgraw, W. S., & Dunbar, R. I. Mountain in Western Saudi M. (2004). A community-level evaluation Arabia. Zoology in the Middle East of the impact of prey behavioural and 14:11- 22. ecological characteristics on predator diet doi:10.1080/09397140.1997.10637699 composition. Proceedings of the Royal Leutenegger, W., & Kelly, J. T. (1977). Society B: Biological Sciences 271:725-732. Relationship of sexual dimorphism in doi:10.1098/rspb.2003.2626 canine size and body size to social, Struhsaker, T. T., & Leakey, M. (1990). Prey behavioral, and ecological correlates in selectivity by crowned hawk-eagles on anthropoid primates. Primates 18:117- monkeys in the Kibale Forest, 136. doi:10.1007/bf02382954 Uganda. Behavioral Ecology and Lewis, K.P. (2000). A comparative study of Sociobiology 26:435-443. primate play behaviour: Implications doi:10.1007/bf00170902 for the study of cognition. Folia Primatologica 71:417-421. Lima, S. L. (1998). Stress and decision making Figures and Captions under the risk of predation: recent developments from behavioral, reproductive, and ecological perspectives. Advances in the Study of Behavior 27:215-290. Figure 1. Play durations (sec.). No doi:10.1016/s0065-3454(08)60366-6 significant difference between Maestripieri, D. & Ross, S. R. (2004). Sex baboons and vervet monkeys. differences in play among western lowland gorillas (Gorilla gorilla gorilla) infants: Implications for adult behavior and social structure. American Journal of Physical Anthropology 123:52-61. Mitani, J. C., & Watts, D. P. (1999). Demographic influences on the hunting behavior of chimpanzees. American Baboons Vervets Journal of Physical Anthropology 109:439-454. doi:10.1002/(sici)1096- 8644(199908)109:4<439::aid- ajpa2>3.0.co;2-3 Pellis, S. M. (1988). Agonistic versus amicable targets of attack and defense: Consequences for the origin, function, and descriptive classification of play- fighting. Aggressive Behavior 14:85- 104. doi:10.1002/1098 2337(1988)14:2<85::aid- ab2480140203>3.0.co;2-5 Platt, M. L., Seyfarth, R. M., & Cheney, D. L. (2016). Adaptations for social cognition in the primate brain. Philosophical Transactions of the Royal Society B: Biological Sciences 371:20150096. doi:10.1098/rstb.2015.0096 UC Davis | EXPLORATIONS: THE UC DAVIS UNDERGRADUATE RESEARCH JOURNAL Vol. 19 (2017) Steinberg p.8

Figure 2. Play bout durations- females. No significant difference between female baboons and female vervets in play duration.

Baboons Vervets

Figure 3. Play bout durations- males. No significant difference between male baboons and male vervets in play duration.

Baboons Vervets

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Figure 4. Play bout durations- baboons. Male baboons played for significantly longer than female baboons on average.

Males Females

Figure 5. Play bout durations- vervets. No significant difference between male and female vervets.

Males Females

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Figure 6. Number of play bouts per minute observed. Baboons played significantly more frequently than vervets did.

Figure 7. Number of play bouts per minute observed- females. Female vervets played significantly more frequently than female baboons, but sample sizes were skewed.

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Figure 8. Number of play bouts per minute observed- males. Male baboons played significantly more frequently than male vervets, but sample sizes were skewed.

Figure 9. Number of play bouts observed-

baboons. Male baboons played

significantly more frequently than female

baboons did.

Figure 10. Number of play bouts observed- vervets. Female vervets played significantly more frequently than female baboons, but sample sizes were skewed.

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