Water Economy and Salt Balance in White-Winged and Inca Doves

Abstract

Two of the most conspicuously abundant birds during the summer in the Sonoran desert regions of southern Arizona and northern Mexico are White-winged Doves (Zenaida asiatica) and Inca Doves (Scardafella inca). These doves have nearly identical general distributions extending over arid parts of the southwestern United States and south through Mexico into Central America. However, within this range Inca Doves are confined to desert towns and villages while White-winged Doves occur throughout the deserts (Ridgway, 1916; Bent, 1932). In addition there are seasonal differences in distribution at least within the United States, with the strong-flying White-winged Doves represented only as spring and summer residents while the relatively sedentary Inca Doves are continuously resident (Bent, 1932). In their enlightening review article on the water economy of land birds, Bartholomew and Cade (1963) indicate an apparent direct relationship between body weight and efficiency of osmotic homeostasis. The differences in body weight between White-winged Doves (ca. 140 g) and Inca Doves (ca. 40 g), together with differences in habitat preference and mobility in the same desert macroenvironment, afforded an excellent opportunity to test the proposed relationship between body weight and water economy in two closely related land birds. Therefore, this study undertakes to examine the water relations of White-winged and Inca doves in light of taxonomic affinity, similarity of macroenvironment, and differences in body size, mobility, and micro-environmental preferences. MATERIALS AND METIIODS The 17 White-winged Doves and 27 Inca Doves used were all collected in or near Tucson, Pima County, Arizona, between September, 1964, and August, 1965. The birds were shipped by air to California, invariably arriving in the laboratory in excellent condition within 24 hours of initial departure. Because of their migratory habits, White~winged Doves were shipped only in the spring and summer months, while Inca Doves were available throughout the year. All birds were placed in a large roof-top aviary, thus subjected to natural photo-period and ambient conditions, and provided in excess with tap water and mixed bird seed. During all phases of experimentation the birds were housed in a window-less room on a 12-hour photoperiod (lights on from 1000 to 2200 hours) with ambient temperature and relative humidity fluctuating between 20-24øC and 35-50 per cent, respectively. The experimental period extended from September, 1964, to November, 1965. Except for the studies of salinity discrimination and utilization of succulent foods, the birds were housed individually in cages measuring 441 The Auk, 83: 441-456. July, 1966