Water Turnover in Roadrunners under Different Environmental Conditions

Abstract

T•ts study reports on the use of tritiated water (HTO) to determine total body water and the kinetics of the water pool in captive Roadrunners (Geococcyx californianus). The Roadrunner is an interesting subject for the study of water turnover, as it occurs in the most arid regions of North America (Grinnell, 1907), consumes primarily animal material (Bryant, 1916), will drink water in the field (Sutton, 1940), but apparently does not require it (Miller and Stebbins, 1964; Ohmart, field observ.). In addition , data on its water losses and requirements are available (Calder and Schmidt-Nielsen, 1967; Calder and Bentley, 1967; Calder, 1968a, 1968b). To our knowledge, this is the first reported attempt to use the HTO (triti-ated water) technique to determine body water loss in nondomesticated or desert dwelling birds under two different environmental conditions. METItODS Three wild-trapped adult and three hand-reared immature Roadrunners obtained near Tucson, Arizona during July 1968 were taken to Davis, California in September 1968 and housed together in a large outdoor cage. Body water turnover was studied under two sets of conditions. In the first experiment, rates of water turnover were determined by following the loss of tritium activity administered intravenously on 10 January 1969. Blood samples were then taken on alternate days through 22 January 1969. The test birds were housed together in an outdoor cage measuring 3 X 3 X 2.3 m. During the first test period, a total of 18.69 cm of precipitation was recorded and the maximal and minimal temperatures ranged from 16 ø to-4øC with a mean of the daily maxima and minima being 8øC. Water vapor pressure during the 13-day test ranged from 5.5 to 3.4 mm Hg with a mean of 4.45 at 8øC, which equals 55 per cent relative humidity. In the second water kinetics experiment, the birds were housed together in a climatically controlled , windowless chamber measuring 3.6 X 2.7 X 2.6 m. The temperature was kept between 30 ø and 32øC. Relative humidity and temperature were monitored continually 13 cm above floor level on a Serdex hygro-thermograph (Bacharach Industrial Instrument Company). Preheated fresh air was delivered constantly into the chamber so that complete air replacement occurred every 3 minutes. We used 11 hours of light during the experiment because it approximated the natural photoperiod. An acclimation period of 15 days was allowed before starting the experiment. HTO was injected on 12 March 1969, and blood samples were obtained through 25 March 1969. During the experiment and the acclimation period, the water vapor pressure calculated at 31øC ranged from 2.0 to 9.43 mm Hg and average 5.72. At 31øC with 5.7 mm Hg, the relative humidity equals 17 per cent. Drinking water was allowed ad libitum in the first experiment. The only water available in the second test was that in the diet of white mice. Following the first water turnover experiment and at the beginning of the second experiment, an injection of 0.5 ml of a 0.9 per cent sterile saline solution containing 1.22 mci/ml of HTO was administered via the right or left brachial vein to each bird. Assuming that the body water pool size, as a per cent of body weight, did not change 787