Abstract
Quantity discrimination has been studied extensively in different non-human animal species. In the current study, we tested 11 hand-raised wolves (Canis lupus) in a two-way choice task. We placed a number of food items (one to four) sequentially into two opaque cans and asked the wolves to choose the larger amount. Moreover, we conducted two additional control conditions to rule out non-numerical properties of the presentation that the animals might have used to make the correct choice. Our results showed that wolves are able to make quantitative judgments at the group, but also at the individual level even when alternative strategies such as paying attention to the surface area or time and total amount are ruled out. In contrast to previous canine studies on dogs (Canis familiaris) and coyotes (Canis latrans), our wolves’ performance did not improve with decreasing ratio, referred to as Weber’s law. However, further studies using larger quantities than we used in the current set-up are still needed to determine whether and when wolves’ quantity discrimination conforms to Weber’s law.
Highlights
Being able to discriminate between different quantities yields advantages for animals’ fitness and survival (Gallistel, 1990)
They were separated from their mothers within the first 10 days of their life, and were hand-raised and socialized at the Wolf Science Center (WSC), am Bundesministerium für Wissenschaft und Forschung (Austria)
Training phase The training phase was conducted to familiarize the animals with the apparatus and the procedure. It consisted of five steps: (1) buzzer training to teach the wolf how to use the experimental apparatus, (2) choosing the larger of two visible quantities (1 vs. 4) presented on the table, (3) discrimination between a visible piece of stone and a visible piece of cheese, (4) same as step 3, but the food and stone were inserted into the opaque cans and were invisible during the choice and (5) choosing once again the larger of two visibly presented quantities (1 vs. 4) to assure that the wolves still chose the larger number after training step 3 and 4
Summary
Being able to discriminate between different quantities yields advantages for animals’ fitness and survival (Gallistel, 1990). In our study (1) the food items were placed one-by-one into an opaque container, thereby avoiding the possibility that subjects made a choice based on seeing the complete quantities of the two sets at the moment of choice, and (2) the handling time during which a smaller vs a larger quantity would be inserted as well as the total amount of items were controlled for by adding additional stones, resulting in equal net quantities of items on both sides.
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