THE EFFECT OF SALT LOADING ON THE PITUITARY PROLACTIN LEVELS OF THE DOMESTIC DUCK (ANAS PLATYRHYNCHOS) AND JUVENILE HERRING OR LESSER BLACK-BACKED GULLS (LARUS ARGENTATUS OR LARUS FUSCUS)

The pituitary prolactin levels were measured in the domestic duck (Anas platyrhynchos) and in juvenile gulls from a mixed population of herring and lesser black-backed gulls. In the domestic duck the pituitary prolactin levels increased on the 2nd and 3rd days of maintenance on 0\m=.\3M-NaCl, but by the 5th day they had fallen appreciably below the control levels. Maintenance ofgulls with 0\m=.\3M-NaCl produced no change in pituitary prolactin levels after 5 days, but a marked fall in prolaction levels when the birds were main-tained on 0\m=.\7M-NaCl for 5 days. This difference in response between the two species may be related to their degree ofadaptation to a marine environment