Birds in marine and saline environments: living in dry habitats

For birds, saline environments such as maritime and salt marsh habitats are essentially dry habitats. When birds drink saline water or consume salt-lo aded preys, the osmolarity of their body fluids increases. In order to main tain the osmotic equilibrium, they have to eliminate the excess of electrol ytes ingested with preys or water. Marine birds use salt glands, which prod uce excretion solutions more concentrated than seawater to eliminate excess salt. The physiology and phenotypic plasticity of nasal glands appears to be correlated with the ecological features of species. Birds can also minim ize osmotic stress by choosing hypo-osmotic preys, preys with reduced water content, and/or by decreasing salt intake. Although the kidney of birds is clearly less efficiently in its capacity to concentrate the urine than tha t of mammals, there are interspecific differences in renal structure and ph ysiology that may be correlated with the birds ecological habits, and hence to represent adaptive mechanism to prevent water loss. The kidney may be e specially important in taxa that lack active salt gland, such as passerines . Passerines, which are supposed to have limited ability to use saline habi tats, include several marine and salt-marsh species. In this review I show that the interaction of the kidney and rectum in osmoregulatory physiology, coupled with selective feeding behavior play a major role in the maintenan ce of water and salt balance of passerines living in salty environments.