Wild chacma baboons (Papio ursinus) remember single foraging episodes.

Understanding animal episodic-like memory is important for tracing the evolution of the human mind. However, our knowledge about the existence and nature of episodic-like memory in non-human primates is minimal. We observed the behaviour of a wild male chacma baboon faced with a trade-off between protecting his stationary group from aggressive extra-group males and foraging among five out-of-sight platforms. These contained high-priority food at a time of natural food shortage. In 10 morning and eight evening trials, the male spontaneously visited the platforms in five and four different sequences, respectively. In addition, he interrupted foraging sequences at virtually any point on eight occasions, returning to the group for up to 2 h. He then visited some or all of the remaining platforms and prevented revisits to already depleted ones, apparently based on his memory for the previous foraging episode about food value, location, and time. Efficient use of memory allowed him to keep minimal time absent from his group while keeping food intake high. These findings support the idea that episodic-like memory offers an all-purpose solution to a wide variety of problems that require flexible, quick, yet precise decisions in situations arising from competition for food and mates in wild primates.

Change point analysis of travel routes reveals novel insights into foraging strategies and cognitive maps of wild baboons.

Efficient space use is a critical challenge for animals relying on stationary resources. It is often difficult with purely observational methods to gain unambiguous insight into any ability of primates to manage and process spatial information. Investigating the visible signs of the decision processes underlying space use often leaves open important issues. We applied the change point test [Byrne et al. (2009). Anim Behav 77: 619-631], a statistical tool to objectively determine change points (CPs) in animal travel paths, to investigate to what degree directional changes in our study group's (Papio ursinus) dry season ranging were associated with important resources and prominent landmarks. One-third of directional changes were associated with fruit feeding, 1/3 with traveling, and 1/3 with dry matter feeding, travel feeding and with drinking. When directional changes were associated with traveling, the subsequent directional changes were likely to result in fruit feeding. Fruit feeding mostly occurred at the apex of the day journeys, while drinking, dry matter feeding, and travel feeding often occurred along straight travel segments. The majority of directional changes did not occur in clusters at distinctive locations, but at distances of more than 120 m apart from each other, many of them along prominent landmarks. We conclude that the CPs do not represent nodes or route bends of a network map. Rather, they represent (1) locations where the decision to turn back to their sleeping site was taken, and (2) locations next to important landmarks (changes of slope, car tracks) where slight adjustment of a movement direction was possible. We found no evidence for a Euclidean map and discuss our findings in the light of a network map representation of space.

Bioacoustic field research: a primer to acoustic analyses and playback experiments with primates.

Acoustic analyses of primate vocalizations as well as playback experiments are staple methods in primatology. Acoustic analyses have been used to investigate the influence of factors such as individuality, context, sex, age, and size on variation in calls. More recent studies have expanded our knowledge on the effects of phylogenetic relatedness and the structure of primate vocal repertoires in general. Complementary playback experiments allow direct testing of hypotheses regarding the attribution of meaning to calls, the cognitive mechanisms underpinning responses, and/or the adaptive value of primate behavior. After briefly touching on the historical background of this field of research, we first provide an introduction to recording primate vocalizations and discuss different approaches to describe primate calls in terms of their temporal and spectral properties. Second, we present a tutorial regarding the preparation, execution, and interpretation of field playback experiments, including a review of studies that have used such approaches to investigate the responses to acoustic variation in calls including the integration of contextual and acoustic information, recognition of kin and social relationships, and social knowledge. Based on the review of the literature and our own experience, we make a number of recommendations regarding the most common problems and pitfalls. The power of acoustic analyses typically hinges on the quality of the recordings and the number of individuals represented in the sample. Playback experiments require profound knowledge of the natural behavior of the animals for solid interpretation; experiments should be conducted sparingly, to avoid habituation of the subjects to the occurrence of the calls; experimenter-blind designs chosen whenever possible; and researchers should brace themselves for long periods of waiting times until the appropriate moments to do the experiment arise. If all these aspects are considered, acoustic analyses and field playback experiments provide unique insights into primate communication and cognition.

How do wild baboons (Papio ursinus) plan their routes? Travel among multiple high-quality food sources with inter-group competition.

How do humans and animals travel between multiple destinations on a given foraging trip? This question is of theoretical and practical interest, yet few empirical data exist to date. We examined how a group of wild chacma baboons travelled among multiple, simultaneously fruiting mountain fig trees (Ficus glumosa). In the course of a 16-month study, this highly preferred fruit was available during a 3-week period, from relatively few sites, which were also utilized by four larger baboon groups. We used directness of route and travel speed of 13 days of observation, and approach rates of 31 days of observation to differentiate between purposeful and opportunistic encounters with 50 fig trees. The study group visited a total of 30 fig trees overall, but only 8 trees per day on average. Each morning, they travelled along a highly repetitive route on all days of observation, thereby visiting 2-4 fig trees. They approached these trees rapidly along highly directed paths without intermittently exploiting other food sources that were available in large quantities. Then, they abruptly changed behaviour, switching to lower travel speed and less directed routes as they foraged on a variety of foods. They approached additional fig trees later in the day, but approach rates were similar to those at times of year when fruit of this fig species was unavailable; this suggested that encounters with trees after the behavioural switch were not planned. Comparing visits to purposefully and opportunistically encountered trees, we found no difference in the average time spent feeding or frequency of feeding supplants, suggesting that purposefully and opportunistically visited trees had similar values. We conclude that when foraging for mountain fig fruit the baboons' cognitive maps either contain information on relatively few trees or of only a single route along which several trees are situated, leading to very limited planning abilities.

Sleep and social status in captive gelada baboons (Theropithecus gelada).

Sleep was investigated in 10 captive gelada baboons (Theropithecus gelada), belonging to two harem groups by continuous infrared video recording (n = 4 males, n = 3 females, n = 3 juveniles). The aim was to investigate the relation between sleep and social status. Social status was assessed during daytime activities, when the two harem groups interacted. Three behavioral states (waking, transitional sleep and relaxed sleep) as well as sleep fragmentation were scored based on movements and body posture. The individuals belonging to each of the harem groups spent most of the night huddled closely together within a sleeping cluster. Sleep was considerably fragmented in all adult and sub-adult individuals. No relation was found between sleep latency or sleep fragmentation and social rank. Total sleep time was 11.4 +/- 0.5 h per night (n = 10) and was negatively correlated with age. In the four males sleep duration was unrelated to their social rank, whereas both within the females and the juveniles it increased with decreasing rank. The amount of relaxed sleep was lower in the dominant males and the dominant females compared to the corresponding low-ranking ones. In contrast, dominant males had the highest amount of transitional sleep, while in the females no rank-association was evident. These results indicate that the high-ranking geladas engaging less in a relaxed sleeping posture may be maintaining a larger degree of alertness that would enable them to react quickly to nocturnal dangers.

Mental maps in chacma baboons (Papio ursinus): using inter-group encounters as a natural experiment.

Encounters between groups of wild chacma baboons (Papio ursinus) can be viewed as a natural experiment to investigate the nature of these primates' mental representations of large-scale space. During a 16-month field study in a high population density habitat we recorded the foraging routes and the most important resources of a group of 25 individuals. Also, we estimated the locations of additional baboon groups relative to the study group. Routes were less linear, travel speed was higher, and inter-resource distances were larger when other groups were present within 500 m of the focal group; thus, the study group avoided others by taking detours. We predicted that evasive manoeuvres would be characteristic of different possible orientation mechanisms, and compared them with our observations. We analysed 34 evasive manoeuvres in detail. In an area that lacked prominent landmarks, detours were small; larger detours occurred when resources were directly visible, or in the vicinity of a hill offering conspicuous landmarks. In areas without prominent landmarks, detours were along familiar routes and waiting bouts of up to 60 min occurred; on one occasion the study group aborted their entire day's journey. We discuss these findings in the light of time and energy costs and suggest that the baboons lack the ability to compute Euclidean relations among locations, but use network maps to find their way to out-of-sight locations.