Coding and Video Analysis

Videos were coded using Noldus Observer XT 9 software, licensed to Professor Andrew Whiten. Continuous variables were coded using an instantaneous (every one second) focal sampling method to capture detailed gaze and locomotion behaviour; point variables were coded using the “all occurrences” sampling method (Altmann, 1974). A coding scheme was created based on schemes used by Held et al. (2002), Hirata and Matsuzawa (2001), Ducoing and Thierry (2003).

Behaviours were divided into general categories: Locomotion, Bait Directed, Gaze Behaviour, Proximity Between Chimps, Dominant Distance to Food, Social Interaction, Visual Access to Partner, Gaze Towards Bait, Absolute Direction, Absolute Gaze (See Appendix 2 for the full coding scheme, as well as an ethogram defining each behaviour). Within each category, there were several different mutually exclusive behaviours; for

example, in the Locomotion category, No Locomotion, Walk, Change Direction, Not Visible, and so on. Certain behaviours had modifiers associated with them; for example, Walk is

modified by Chimp (Closer/ Further) and Bait (Towards/ Away). Absolute movement codes noted which of the four quadrants the subject was currently in, which quadrant she was moving towards (or, if not moving, a zero was entered), and whether a food item was hidden in that direction. The set of absolute codes is more specific than the relative codes, and it helps to support relative codes.

For the analyses in the following chapters, a selection of the variables was tested (Table 3.5).

Table 3.5: Variables and definitions

Variable name Definition

Locomotion towards the bait The subject moved (walk/run/climb) in the relative direction of the hidden food

Gaze towards the bait The subject directed her gaze in the relative direction of the hidden food

Locomotion towards a quadrant The subject moved (walk/run/climb) in the absolute direction of a specific quadrant of the enclosure

Gaze towards a quadrant The subject directed her gaze in the absolute direction of a specific quadrant of the enclosure

Locomotion towards the opponent The subject moved (walk/run/climb) in the relative direction of the other chimpanzee

Locomotion away from the opponent The subject moved (walk/run/climb) in the relative direction away from the other chimpanzee

Look at the opponent The subject looked directly at the other chimpanzee In the same quadrant Both subjects are located in the same quadrant of the

enclosure

In different quadrants Both subjects are located in different quadrants of the enclosure

Going towards the same quadrant Both subjects are moving (walk/run/climb) in the absolute direction of the same quadrant of the enclosure Change direction The subject changed her absolute direction of movement Change gaze direction While in view of the opponent, the subject changed her

absolute direction of gaze

Gaze towards same quadrant Both subjects directed their gaze in the absolute direction of the same quadrant of the enclosure

Stop locomotion The subject stopped moving for five consecutive seconds Stop gaze towards the bait The subject stopped gazing towards the food for five

consecutive seconds

Monitoring glances The subject looks at the opponent and then gazes towards the bait for two consecutive seconds

Recruitment glances The subject looks at the opponent and then gazes towards the bait for two consecutive seconds, and stops

III. Methods: Informed Forager Experiment 2: Unequal Rewards

A. Subjects

The same pairs of chimpanzees that participated in Experiment 1 also participated in Experiment 2: Missy and Rita, and Reinette and Georgia.

B. Setting

The setting for the second experiment was the exact same as in Experiment 1: the dominant was locked in the Ignorance Cage of the ‘Cognition Room’ and the subordinate was locked in the Knowledge Cage #1 during baiting. All other chimpanzees were locked into the Bedroom area on the other side of the enclosure where they could not see the experimental procedure.

C. Experimental Design

For this experiment, both a banana and a cucumber were hidden on each trial to determine whether a reward of lower preference, the cucumber, would have an effect on the subordinate’s behaviour. I expected that, though each individual subject preferred banana to cucumber, the knowledgeable subordinate should approach the cucumber before the banana within each trial, with the (learned) expectation that the dominant would follow and

subsequently take the reward. Hence, if the dominant took the cucumber, the subordinate would still have a chance to win the banana.

From the original list of 16 hiding places, two places had to be changed due to safety concerns with human experimenters climbing on the structure during baiting: Q1-Hose nozzle became Q1-Hammock, and Q2-Tower became Q2-Box. Once these changes were made, a list of eight pairs of places was devised for hiding bananas and cucumbers. The hiding spots were semi-randomized such that each bait was hidden twice in each of the four quadrants during the first eight trials, then the same list was used for the subsequent eight trials, with the location of the banana and cucumber reversed. Thus, the banana was hidden once in all 16 places, as was the cucumber. Pairs were counterbalanced for side of enclosure: no two rewards were hidden together on the left (Q1, Q3) or the right side of the enclosure (Q2, Q4) because of the possibility that a subject would find the reward closer to their starting position first, regardless of preference.

Once the list was made, the order was again randomized for the pairs of competing chimpanzees, to control for order effects across pairs. An example of the Missy-Rita baiting schedule is printed below in Table 3.6 for trials 1-8; for trials 9-16, the cucumbers were

hidden in the locations in the first column and the bananas were hidden in the locations in the second column (reversed); for the final trials 17-20, the rewards were again hidden in their original order. Each pair competed for 20 trials.

TABLE 3.6: List of hiding places for bananas and cucumbers per trial, Pair 1

BANANA CUCUMBER

Q4 Small tire Q1 Hammock Q2 Tire Q3 Red ring Q3 Culvert Q4 Kegs

Q2 Cone Q1 White barrel Q1 Culvert Q4 Red ring Q3 Hanging tire Q2 Ladder joint Q1 Tire Q2 Behind lixit Q4 Culvert Q3 Kegs

D. Procedure (for each condition)