Food choice by white-tailed deer in relation to protein and energy content of the diet: a field experiment

Abstract

Optimality models of food selection by herbivores assume that individuals are capable of assessing forage value, either directly through the currency used in the model or indirectly through other variables correlated with the currency. Although energy and protein are the two currencies most often used, controversy exists regarding their respective influence on food choice. Part of the debate is due to the difficulty of teasing apart these two nutrients, which are closely correlated in most natural forages. Here we offer a test of the assumption that energy and protein contents of the forage are both currencies that large mammalian herbivores can use when selecting their food. We observed feeding behavior of 47 wild white-tailed deer (Odocoileusvirginianus) during winter while individuals were presented with four experimental foods representing two levels of energy and protein (dry matter digestibility: 40-50%; crude protein: 12-16%). Using experimental foods allowed us to separate the influences of energy and protein and clearly distinguish between the roles of these two nutrients. Deer discriminated between foods through partial selection, and selected diets higher in energy but lower in protein. The observed choices appeared consistent with physiological needs of deer wintering at the study site, where digestible energy was in short supply in the natural environment while protein was probably not. Results are in good agreement with recent findings on domesticated ruminants. They support a basic assumption of optimality models of food selection that use energy and/or protein as a currency, although the physiological mechanisms behind the food selection process remain unclear. We urge students of food selection by herbivores to replicate our experiment with other foods and/or in other circumstances before more general conclusions are drawn.

Interactions between ungulates, forests, and supplementary feeding: the role of nutritional balancing in determining outcomes

“…Nutritional balancing is found in an increasingly diverse group of animals and involves the altering of food intake on a daily or near daily basis to achieve a specific nutritional target balance in the diet, either by selecting nutritionally balanced food items or by combining food items with compositions complimentary to each other (e.g., Felton et al 2009;Mayntz et al 2009;Rothman et al 2011;Simpson and Raubenheimer 2012). This regulatory feat is explained by several neural and chemical processes and feedbacks operating before, during, and after digestion (Berteaux et al 1998;Provenza 1995).…”

Influence of agricultural crops adjacent to forest on woody species browsing: Is it advantageous to have a tasty neighbour?

“…Selection of the diet higher in energy but lower in protein was proved by using experimental foods in free living white-tailed deer in Canada. In this experiment nitrogen levels ranged from 1.8 to 2.6% and deer were able to discriminate between experimental foods and preferred foods higher in digestible energy or at each given level of digestible energy the foods lower in nitrogen (Berteaux et al 1998). For this we collected samples from both agricultural crops and spruce and beech.…”

Role of early experience in the development of preference for low-quality food in sheep

“…When confronted with a choice of foods, ruminant have the ability to select the most nutritious alternatives (Provenza, 1996;Berteaux et al, 1998;Villalba and Provenza, 2000). In grazing conditions this behavior leads to persistent selection of plant species of high nutritional quality, thus altering the botanical composition of pasturelands and limiting subsequent selection by animals (Milchunas et al, 1988;Provenza et al, 2003).…”