Quantity Discriminatory Capacity and Choice Preference Between Binary Rewards in African Elephants

Abstract

The ability to quantitatively discriminate between different numbers of the same items is shared by most animals and pre-verbal humans, and it is a requirement for being able to do simple arithmetic operations. This thesis investigated African elephants’ (Loxodonta africana) ability to do simple arithmetic by testing their quantity discrimination ability, potential drivers of it, and their learning ability, with a special focus on individual differences. The results from this thesis provide informative priors representing a necessary foundation to quantitatively estimate the risk preferences of elephants in further choice tasks, which is the aim of the larger project this thesis is part of. Individual elephants were presented with binary choices over different quantities of the same food. All data analysis used a Bayesian framework, to allow informed inferences about individual elephants. First, the preference of the elephants for different fruits was measured. Subsequently, using game pellets and the preferred fruits, quantity discrimination choices were observed using olfactory-only or olfactory-and-sound as cues. Elephants were successful in discriminating between different quantities based on olfactory cues only, but only when they could smell directly on the top of the perforated buckets containing the rewards. A combination of olfactory information and sound reduced their discrimination ability. The absolute difference between the alternatives had a stronger effect on the choices made by the elephants when the difference between the alternatives was larger, while the ratio of the alternatives affected the choices mostly when the two alternatives were similar in size, regardless of the food used. This finding suggests that elephant olfactory quantity discrimination was driven mainly by the numerosity of the rewards rather than by the idiosyncratic characteristics of the food. Grouping the quantity discrimination evidence over each reward together, I was able to show that elephants can perform simple arithmetic operations, being more precise when the alternatives differ by at least two units. The learning ability of the elephants was affected by the order and difficulty of the tasks, with initial tasks, when elephants were not accustomed to the experimental set-up yet, showing clear indication of learning. The fact that the elephants in this study were able to successfully discriminate between different quantities of different fruits, that they were relatively precise when the difference between the alternatives was at least 2 units, and that they showed signs of learning over the course of novel tasks, allows one to infer that eliciting the risk preferences of elephants might be possible. In addition to representing the first step to a quantitative elicitation of the risk preferences of elephants, this thesis proves for the first time that African elephants can do simple arithmetic and also provides vital information to increase our understanding of how elephants make decisions in the wild.