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 mammalian herbivores. Moreover, consumption of various plant secondary metabolites has been associated with negative sodium balance in mammals. Neither of these issues has been investigated in birds, which differ from mammals in their ion-exchange processes and postrenal absorption of urine. Our objectives were to determine if ruffed grouse (Bonasa umbellus) 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 compromises a bird's sodium balance. Captive ruffed grouse were fed either aspen buds (0.063 mg∙g−1 sodium) or a formulated diet having different concentrations of coniferyl benzoate in no-choice feeding trials. Sodium excretion did not change in response to coniferyl benzoate intake or acid load from detoxication processes; however, birds were marginally 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 foods (0.065 mg∙g−1) indicated that these birds likely maintained sodium 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, which is lower than the minimum sodium requirements for poultry and mammals.