Plant secondary compounds and the frequency of food types affect food choice by mammalian herbivores

We have investigated food choice in individual fallow deer (Dama dama) encountering different relative frequencies of food types in the form of bowls containing pellets with either high or low concentrations of hydrolyzable tannin. We performed two similar experiments, one with large and one with small differences in tannic acid concentration. With small differences in tannic acid concentration, the ratio of the consumption per low- and high-tannin bowl was independent of frequency of occurrence, but with large differences in tannic acid concentration, we found frequency-dependent food choice. The deer ate proportionally less from high-tannin bowls if these occurred at low relative frequency. Variation between frequency treatments in the average order of encounter of bowl types might have produced this effect, because we found that the deer left a high-tannin bowl more quickly if they had switched to it from a low-tannin bowl. We argue that the perceived contrast between the tastes of different food types can play a role for food choice by mammalian herbivores.