Summer water turnover rates in free-living chukars and sand partridges in the Negev Desert.

Alectoris chukar and Ammoperdix heyi are permanent residents of the Negev desert, Israel. They are sympatric between the 200 and 90 mm isohyets, with only sand partridges occurring in more arid areas. During the dry season, the authors measured total body water volume (TBW; as tritiated water spacce) and total water turnover rate, and estimated dry matter intake and components of water turnover in free-living birds of both species. Mean body mass (m_{) of 40 chukars was 460.8 g and of 42 sand partridges was 176.6 g. TBW, as a percentage of mb, was lower in chukars than in sand partridges (67.4% vs. 69.8%). Mean water turnover was 44.1 ml/day for chukars and 20.8 ml/day for sand partridges. The mass-specific water turnover rate was higher in sand partridges than in chukars (122.5 ml kg^-1 day^-1 vs. 100.6 ml kg^-1 day^-1). However, when compared allometrically, per kg^0.75, water turnover rates were similar (81.7 ml.kg^-10.75 day^-1 for chukars vs. 78.5 ml kg^-0.75 day^-1 for sand partridges). Assuming a diet of seeds it is calculated that drinking water amounted to c70% of water turnover in both chukars and sand partridges. Both species must drink water when only dry forage is available.-Authors}