The Effect of Salt Intake on the Size and Function of the Salt Gland of Ducks

Abstract

The salt gland or nasal gland of marine birds is capable of eliminating sodium chloride as a highly concentrated solution. This enables these birds to tolerate the ingestion of sea water or food with a high salt content. Terrestrial birds, which lack an extra-renal excretory mechanism have, in general, a low tolerance to salt because their kidneys cannot produce a urine with high salt content. Apparently all marine birds have utilized the extra-renal mechanism for salt elimination; an increased renal capacity for salt excretion does not seem to have been a feasible evolutionary ap- proach to this problem. The few passerine birds that have a high salt tolerance, however, seem to represent an exception that may provide inter- esting material for the student of avian evolution.