Selection for Small Amounts of Hydrolysable Tannins by a Concentrate-Selecting Mammalian Herbivore

Abstract

Although herbivores usually avoid plants with high concentrations of tannins, roe deer in natural habitats select tannin-rich plants. We tested the hypotheses that: (H1) roe do not seek tannins, rather they select for other (unmeasured) factors such as minerals or vitamins; and (H2) roe do select for tannins. Tame roe deer were offered a choice of food pellets to which hydrolyzable chestnut tannins had been added or control pellets. The daily consumption of pellets containing a high level of tannins (9.1%) was lower than consumption of control pellets. However, when offered medium level tannin pellets (3.8%), roe deer ate more tannin than control pellets. Moreover, the roe regulated their intake of these tannins closely. The regression of tannin intake versus total pellet intake across all the tests was linear and precise (r ² = 0.94): intake was about 28 g of tannin per kilogram of pellets eaten. We therefore reject H1 and suggest that roe can monitor tannin concentrations in their food, and regulate their intake precisely. The results suggest that a certain level of tannins induces no costs or that they provide a nutritional benefit for roe deer.