Use of Sodium Chloride Solutions by the Brewer's Sparrow and Tree Sparrow

Abstract

SEVERAL studies of the ability of birds to use solutions of sodium chloride have been reported in recent years (Bartholomew and MacMillen, 1960; Cade and Dybas, 1962; Poulson and Bartholomew, 1962a, 1962b; Dawson et al., 1965; Smyth and Bartholomew, 1966; Willoughby, 1966). The majority of this research has dealt with distantly related granivorous inhabitants of desert or semiarid regions. No extensive studies have been made to examine a taxon containing a number of seedeating species that show a broad ecological divergence. The earlier studies of Poulson and Bartholomew (1962b) and Cade and Bartholomew (1959) on the Savannah Sparrow (Passerculus sandwichensis) approached this, but only 5 of the some 16 races were ever examined. This paper reports on two species in the genus Spizella and is the first in an attempt to examine all the species comprising this taxon. On completion we hope to have a clearer understanding of the use of sodium chloride solutions as an index of renal efficiency and added knowledge on the evolution of physiological systems. The objectives of this study were to compare the ability to use sodium chloride solutions by two species of Spizella that occupy widely divergent habitats with respect to the availability of free water. Brewer's Sparrow (S. breweri), both on its wintering and breeding grounds, occupies areas often far removed from free water. The Tree Sparrow (S. arborea), on the other hand, occupies a much more mesic habitat where succulent plant material and/or free water are normally always available.