Seasonal variation in size and function of the nasal salt gland of the franklin's gull ( Larus pipixcan)

Abstract

1. 1. Extrarenal salt excretion through the nasal gland allows marine birds to drink salt water. Species inhabiting fresh water usually have small glands, although in many species studied, the glands increase in size in response to salt loads. 2. 2. The Franklin's gull ( Larus pipixcan) breeds in freshwater habitats and winters in marine habitats. Accordingly it shows an annual cycle in the size and function of the nasal gland. We found a large and active gland in gulls collected in April (just after arrival on the breeding ground) and in October (just prior to migration), while birds collected from late May to July had small and apparently inactive glands. 3. 3. Recrudescence of the gland occurred in wild-caught adults maintained in captivity on fresh water without a salt load. 4. 4. This appears to represent a cyclical phenomenon that is independent of actual salt loading. 5. 5. The glandular hypertrophy produced a histological picture similar to that of adaptive hypertrophy in response to salt loading. 6. 6. The increase was not inhibited by maintaining birds on a constant 16:8 light/dark cycle. This change is analagous to size changes in avian gonads. 7. 7. This cyclical phenomena may preadapt the Franklin's gull's salt gland to handle the slat load it will encounter when it reaches its winter quarters on the Pacific ocean shore.