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

Abstract

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.METHODS BREWER'S SPARROW The 60 Brewer's Sparrows used in the tests reported here were netted near Tucson, Arizona from January through March of 1966 and 1967 and were referable to nominate S. b. breweri.Measurements of ad libitum consumptie.n of distilled water and NaC1 solutions up through 0.45 M were made in late 1966 and early 1967.Tests on 0.5 and 0.55 xr sodium chloride solutions and dehydration studies were completed after obtaining new test animals in 1967.Netted birds were held in outside aviaries for a week or longer before being placed in individual cages measuring 22 X 22 X 37 cm.The cages were housed in a windowless chamber in which the temperature was controlled between 20 ø and 21øC.The photoperiod extended from 12:OO to 24:00.The relative humidity during the experiments ranged from 20 to 70 per cent with the majority of the readings being near 70.The relative humidity remained between 32 and 42 per cent during the test in which the birds were maintained at 25øC with no fluid for drinking.All tests were conducted for 21 days except in the experiments with no water at 25øC and with the 0.45 • solution which lasted 14 and 17 days, respectively.