SODIUM-BALANCE IN RUFFED GROUSE AS INFLUENCED BY SODIUM-LEVELS AND PLANT SECONDARY METABOLITES IN QUAKING ASPEN

Forages in boreal ecosystems are often deficient in sodium for mammali an herbivores. Moreover, consumption of various plant secondary metabo lites has been associated with negative sodium balance in mammals. Nei ther of these issues has been investigated in birds, which differ from mammals in their ion-exchange processes and postrenal absorption of u rine. Our objectives were to determine if ruffed grouse (Bonasa umbell us) can maintain sodium balance on quaking aspen (Populus tremuloides) flower buds, an important winter food, and to determine if the buds' primary plant secondary metabolite (coniferyl benzoate) further compro mises a bird's sodium balance. Captive ruffed grouse were fed either a spen buds (0.063 mg . g(-1) sodium) or a formulated diet having differ ent concentrations of coniferyl benzoate in no-choice feeding trials. Sodium excretion did not change in response to coniferyl benzoate inta ke or acid load from detoxication processes; however, birds were margi nally in negative sodium balance (P = 0.035; -5.06 +/- 2.05 mg . kg(-1 ). d(-1)) when feeding on aspen buds. Sodium levels in the feces from free-ranging grouse (0.050 +/- 0.0 mg . g(-1)) and in their winter foo ds (0.065 mg . g(-1)) indicated that these birds likely maintained sod ium balance. We estimated that free-ranging ruffed grouse may need as little as 7 mg . kg(-1). d(-1) of sodium to maintain sodium balance, w hich is lower than the minimum sodium requirements for poultry and mam mals.