Inter- and intraspecific variation in the use of marine food resources by three Cinclodes (Furnariidae, Aves) species: Carbon isotopes and osmoregulatory physiology
The avian genus Cinclodes (Furnariidae) includes species that inhabit both inland and marine shores. We compared the carbon isotopic
composition and osmoregulatory capacities of field caught individuals of three Cinclodes species in Chile. Cinclodes nigrofumosus is a
resident of coastal shores, whereas C. oustaleti and C. patagonicus inhabit both coastal and inland environments. The tissues of C. nigrofumosus exhibited distinctively marine δ13C values, whereas those of C. oustaleti and C. patagonicus were intermediate between
marine and terrestrial values. The differences in carbon isotopic composition among these three species were paralleled by differences
in osmoregulatory characteristics. The species that carbon isotopes revealed to be strictly marine, C. nigrofumosus, had relatively larger
kidneys with a higher fraction of total renal tissue occupied by medullary cones than its congeners C. oustaleti and C. patagonicus. Cinclodes nigrofumosus individuals also produced more concentrated urine. In addition to interspecific differences in osmoregulation, we
found intraspecific differences. Cinclodes nigrofumosus collected at an arid site with limited or no available fresh water exhibited larger
kidneys and higher relative medullary thickness than individuals collected at a mesic site. Cinclodes nigrofumosus, like all passerines,
lacks functional salt glands. This species appears to be unique among passerines in its ability to live in extreme arid coastal environments and to cope with a marine diet that imposes high osmotic loads.
Inter- and intraspecific variation in the use of marine food resources by three Cinclodes (Furnariidae, Aves) species: Carbon isotopes and osmoregulatory physiology