USE OF AQUATIC PLANTS BY MOOSE - SODIUM HUNGER OR FORAGING EFFICIENCY

Use of submergent aquatic plants by North American moose (Alces alces) has been linked to sodium hunger. Habitat preferences, seasonal diets , forage abundance and quality, and population surveys indicated that emergent plants in small shallow ponds were important to moose on the Copper River Delta, Alaska. However, sodium was abundant in terrestria l browse. We propose that foraging in aquatic habitats, particularly o n emergent species, may be highly efficient based on the following hab itat attributes and behavioral observations: (i) ponds dominated by ei ther emergent or submergent species produced about 4 times more forage than terrestrial habitats, (ii) emergent and submergent plants were m ore digestible and had higher concentrations of minerals than browse, (iii) use of aquatic habitats followed trends in forage production ove r the growing season, (iv) indirect evidence suggested that forage int ake rates were greater in aquatic habitats, and (v) use of aquatic hab itats by male and female moose was in proportion to the sex structure of the population. These data provide consistent circumstantial eviden ce that use of emergent species, and possibly submergents, may maximiz e the intake of nutrients and also reduce conflicts between cropping f orage and vigilance during a foraging bout.