Observations on Metabolism of Sodium Chloride in the Red Crossbill

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Abstract
The ad libitum intake of tap water by red crossbills (Loxia curvirostra sitkensis) equals 21% of body weight/day. When deprived of fresh water, their utilization of NaCl solutions as fluid sources conforms to the pattern observed in the mourning dove and several passerines. Rate of fluid intake increases with salinity up to a point and individuals may come to ingest more than their body weight of salt water daily. Beyond 0.250 [image] NaCl, crossbills tend to reduce their drinking despite severe loss orweight. The maximum concentration on which these birds can maintain weight is near 0.2 [image]. Red crossbills show no significant preference between distilled water and 0.100 [image] NaCl when supplied with both for drinking. However, they strongly prefer water to 0.200 [image] NaCl. The plasma Na concentration of crossbills in water balance is 162 meq/liter. This rises when the birds are forced to obtain their fluid from NaCl solutions more concentrated than 0.200 [image]. Urinary Na concentrations for birds maintained on tapwater were well below plasma concentrations of this cation. The respective urinary concentrations for birds drinking 0.174 to 0.300 [image] NaCl averaged slightly higher than the Na concentration of the fluid ingested. Acute salt loads were applied by injection of 10% NaCl into the brachial vein. The injected NaCl appears to equilibrate with total body water rather than with just extracellular fluid. Birds receiving 0.1 to 0.6 mg/g by injection did not excrete more than half of the load over 6 hours. The associated urinary water loss and evaporative loss prevented this excretion from alleviating the hypernatremia induced by salt loading.