Aquatic feeding by moose: selection of plant species and feeding areas in relation to plant chemical composition and characteristics of lakes

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Abstract
Aquatic feeding by moose was studied with emphasis on (i) the chemical composition of aquatic plants compared with terrestrial browse, (ii) the chemical composition of preferred and unpreferred aquatic plant species, and (iii) characteristics of preferred feeding areas. Compared with woody browse, aquatic plants had much higher levels of sodium and iron, and similar levels of other nutrients tested. In a "cafeteria" selection experiment, moose consistently ate seven species of aquatic plants (preferred plants), consistently rejected five species (unpreferred plants), and gave an intermediate response to seven species. Preferred species had significantly higher sodium content. Those in the intermediate class contained more crude protein and phosphorus than unpreferred species. Of 24 lakes and ponds, 6 were heavily used by moose, 16 were used relatively little, and 2 were difficult to classify. The six heavily used sites had shallower water, a higher mineral content in the lake sediment, and a greater abundance of preferred plant species. Plants growing in heavily used sites had higher levels of sodium, phosphorus, and manganese than the same species growing in lightly used sites. Results suggest that levels of sodium in aquatic plants have a major influence on the animals' selection of aquatic plant species and feeding areas, while phosphorus and protein levels may also influence selection.