Excretory organ growth and implications for salt tolerance in hatchling American avocets Recurvirostra americana

The role of salt glands in avian osmoregulation has been widely studied. Acclimation to saline habitats in aquatic birds involves increases in the relative size and complexity of the salt glands, and it is generally agreed that salt gland size varies as a function of salt loading, and is broadly correlated with habitat salinity. We report here salt gland sizes in three age classes of American avocet Recurvirostra americana chicks. Mean relative (mg/g body mass) salt gland masses for newly hatched (<24 h old) avocet chicks collected at a wetland supplied with pumped fresh water was 0.48 mg salt gland/g body mass. This value is comparable to the low end of published values for some strictly marine birds and similar to values for adult American avocets collected at saline lakes. These results suggest that American avocets, which are frequently raised in saline environments, hatch with salt glands that are large enough to cope with the osmoregulatory demands of saline environments.