The effect of salt gland removal on cloacal ion and water excretion in the growing kittiwake, Rissa tridactyla

Abstract

The supraorbital salt glands were surgically removed from five nestling kittiwakes, Rissa tridactyla, which, with four sham-operated birds, were reared in individual cages for 29 days on a diet of weighed fish. The daily cloacal excreta were weighed and analyzed for Na+, K+, Cl−, and water. Salt gland removal did not greatly affect cloacal ion excretion. In both groups cloacal fluid contained 30% of the ingested water and 20–50% of the ingested ions. The cloacal fluid of control birds was always hypotonic to the food, that of glandless birds hypertonic. In all samples the solid excreta (mainly uric acid) comprised 10% of the weight, but contained 25–50% of the cloacally excreted Na+ and Cl− and up to 60% of the K+. Fecal material might account for 10% of the ingested NaCl. Since cloacal excreta contained only one-half of the ingested ion load, extrarenal salt excretion may still have existed in the kittiwakes lacking supraorbital salt glands. These birds did not secrete after acute salt loading, but the plastic cage liners of these birds had nearly as much NaCl on them as did those of control birds, suggesting secretion from the head region. The tears were approximately isotonic to the plasma. Salt gland removal did not affect adrenal, lacrymal, or Hardenian glands, kidney, or body weight, but glandless birds had slightly larger hearts.