Although songbirds (Order Passeriformes) have diversified in all continents and now occupy nearly all terrestrial ecosystems (Barker et al . 2004), few songbird species inhabit marine environments (Sabat 2000). To our knowledge, and with the exception of one of the species described here, there are no reports of passerine species that rely exclusively on marine diets (Sabat, Fariña & Soto- Gamboa 2003). Several subspecies of Savannah Sparrows ( Passerculus sandwichenis ) can be considered ‘marine’ because they inhabit salt marshes with scarce fresh water (Wheelwright & Rising 1993). Salt-marsh Savannah Sparrows have remarkable abilities to tolerate dry and salty environments (Poulson & Bartholomew 1962; Goldstein, Williams & Braun 1990), but because they feed primarily on the seeds of terrestrial plants and on insects they cannot be considered strictly marine (Wheelwright & Rising 1993). Some of the reasons for the extreme paucity of marine species among the passerines may be ecological and include competition with non-passerine birds. There is, however, a potential physiological cause for the relative scarcity of marine species among passerines. Feeding on salty marine foods may be challenging for passerines without functional salt glands and with limited ability to concentrate urine (Goldstein & Skadhauge 2000)...
