Diet choices made by free-ranging moose in northern Sweden in relation to plant distribution, chemistry, and morphology

Abstract

Understanding how large herbivores select their diet requires accurate measurements of the nutritional costs and benefits of food items and the composition of plants in the diet relative to the composition of plants in the habitat. We followed moose (Alces alces) tracks in the snow and measured bites of browse plants taken and the number and mass of twigs of the 10 browse species available within the moose's reach and measured morphological and chemical characteristics of browse plants. The diets of 41 moose in northern coastal Sweden contained 75% Scots pine (Pinus sylvestris) and willow (Salix spp.), with the remaining proportion equally divided among five deciduous browse species and common juniper (Juniperus communis). The moose used approximately 20% of the bites available along the foraging patch, usually taking only one or two bites on each plant selected for browsing. Moose selected rowan (Sorbus aucaparia), willow species, and aspen (Populus tremula) in winter, used gray alder (Alnus incana), silver birch (Betula pendula), and Scots pine in proportion to their availability, and avoided pubescent birch (Betula pubescens) and Norway spruce (Picea abies). Selection was correlated with plant morphology but not with digestibility or nitrogen, fibre, or phenolic content. Moose selected browse species offering fewer, larger stems over those with many, smaller stems. Moose made slight adjustments in their food selection and foraging intensity as abundance of browse plants declined, thereby presumably maintaining higher harvesting rates.