Revista Chilena de Historia Natural 76 (2): 335-343, 2003
RESEARCH ARTICLE
Terrestrial birds living on marine environments: does dietary composition of Cinclodes
nigrofumosus (Passeriformes: Furnariidae) predict their osmotic load?
Feeding on saline marine foods may be especially challenging for passerine birds that
lack functional salt glands and have a limited ability to concentrate urine. To reduce the salt load imposed by consumption of marine
food these birds may select food with low salt contents and/or increase their intake of freshwater. The genus Cinclodes is
particular among passerines because it includes species that inhabit both inland and maritime shores. We analyzed the diet of
Cinclodes nigrofumosus and explored the possible relationships between dietary composition and salt load at mesic and
arid coastal sites of Chile. From a biogeographical perspective, we hypothesized that freshwater availability is critical to the relationship
between diet composition and osmotic load of C. nigrofumosus. Our analysis of prey abundance and distribution
indicated that the diet of C. nigrofumosus is composed mainly by marine prey, in spite of the availability of terrestrial
insects at both sites. Stomach content osmolality was higher in the arid site, but it was not correlated with prey type, which suggests
that Cinclodes nigrofumosus avoid a high osmotic load, drinking fresh water when available. Thus physiological
constraints are modulating niche breath of Cinclodes.
Key words:
Cinclodes,
dietary habits, osmoregulation, osmotic load
