Energy Intake by Hydropenic Chipping Sparrows (Spizella passerina passerina) Maintained on Different Diets

Abstract

Water deprivation tests have been used to study the physiological capabilities of small desert birds to remain in water balance when maintained solely on a dry diet of seeds. In order to survive such conditions, a bird must employ certain physiological and behavioral adjustments so that water loss through evaporation and excretion is minimized to a point where it can be balanced by metabolic water and water ingested with the food. In addition, the seeds must be mechanically processed and assimilated to satisfy energy requirements, even though water is not readily available. Several species are capable of maintaining water and energy balance for prolonged periods without free water (Smyth and Bartholomew 1966; Ohmart and Smith 1971). However, little work has been done on the effects of water restriction and deprivation on avian energy balance. In some birds, gross energy intake and excretory energy output are altered during water deprivation and restriction (Willoughby 1968; McFarland and Wright 1969; Moldenhauer and Wiens 1970), but little is known about the ecological implications and relationship of these two values before and after deprivation. Furthermore, comparisons have been hindered by the diversity of the diets utilized in water economy studies. These diets include mixed bird seed (Bartholomew and Cade 1956), commercial millet (Willoughby 1968), chick starter mash (MacMillen and Snelling 1966; Moldenhauer and Wiens 1970; Anderson 1970), or combinations of these (Poulson and Bartholomew 1962; Ohmart and Smith 1971), all of which differ in texture, protein and salt content, and calorific value. Perhaps these different diets affect the outcome of water economy studies, resulting in data which may not be truly comparable. This study provides information on the effects of water restriction, water deprivation, and diet on the energy balance of the eastern Chipping Sparrow (Spizella passerina passerina). MATERIALS AND METHODS