Quantity judgments in the context of risk/reward decision making in striped field mice: first “count,” then hunt

Abstract

We simulated the situation of risky hunting in the striped field mouse Apodemus agrarius in order to examine whether these animals are able to make a choice between small and large quantities of live prey (ants). In the first (preliminary) experiment we investigated to what extent mice were interested in ants as a live prey and how their hunting activity depended on the quantity of these edible but rather aggressive insects. We placed mice one by one into arenas together with ant groups of different quantities, from 10 to 60. Surprisingly, animals, both wild-caught and laboratory-reared, displayed rather skilled predatory attacks: mice killed and ate from 0.37 ± 003 to 4 ± 0.5 ants per minute. However, there was a threshold number of ants in the arenas when rodents expressed signs of discomfort and started to panic, likely because ants bit them. This threshold corresponds to the dynamic density (about 400 individuals per m2 per min) in the vicinity of anthills and ants' routes in natural environment. In the second experiment mice had to choose between different quantities of ants placed in two transparent tunnels. Ants here served both as food items and as a source of danger. As far as we know, this is the first experimental paradigm based on evaluation of quantity judgments in the context of risk/reward decision making where the animals face a trade-off between the hedonistic value of the prey and the danger it presents. We found that when mice have to choose between 5 vs. 15, 5 vs. 30, and 10 vs. 30 ants, they always tend to prefer the smaller quantity, thus displaying the capacity for distinguishing more from less in order to ensure comfortable hunting. The results of this study are ecologically relevant as they reflect situations and challenges faced by free-living small rodents.

Numerical assessment in the wild: insights from social carnivores

“…Researchers in these fields have found that the ability to discriminate between different numbers of objects appears to be a foundational cognitive ability and have documented this ability in numerous species across the Animal Kingdom. For example, quantity discrimination has been demonstrated experimentally in several species of fish [5,11,[19][20][21], amphibians [8,22,23], birds [18,[24][25][26][27][28][29][30][31][32][33][34][35], mammals [9,[36][37][38][39][40][41], primates [42][43][44][45], human infants [46][47][48][49] and even some invertebrates [50][51][52]. The only study testing quantity discrimination in a reptile found that although ruin lizards (Podarcis sicula) do spontaneously select the larger quantity of food, they do not spontaneously select the option with a higher number of food items [53].…”

Guppies discriminate between two quantities of food items but prioritize item size over total amount

“…Although in a few cases small groups of prey are more profitable than large ones (Panteleeva et al, 2013), generally foragers would be expected to benefit from recognizing and selecting larger food sources. Depending on the context, this may imply choosing the larger food item (Beran, Evans, & Harris, 2008), the patch with more food items, i.e.…”

Quantity discrimination in parental fish: female convict cichlid discriminate fry shoals of different sizes

“…Lions and chimpanzees, for example, can assess the relative numerosity of a rival group to avoid conflicts with stronger opponents (McComb et al 1994;Wilson et al 2001). Numerical ability can also be used to select a group of prey that is more vulnerable to predatory attack (e.g., Panteleeva et al 2013).…”