Responses to Saline Drinking Water in Two Desert Phasianids the Chukar and the Sand Partridge

Abstract

Responses to the ingestion of saline drinking water in the sand partridge (Ammoperdix heyi), a phasianid of arid and very arid areas, and the chukar (Alectoris chukar sinaica), a phasianid inhabiting deserts only at the margins of its wide mesic range, were compared. Both species lost body mass (mb) when drinking ad lib. NaCI solutions of 0.3 M or greater, but the rates of body mass decline were less in sand partridges than in chukars. Two of four chukars died after drinking 0.4 M NaCl for 6 days; however, four sand partridges survived after drinking 0.5 M NaCl for 10 days. Sand partridges drinking 0.3 M and 0.4 M NaCI lost body mass slower than ones deprived of water (0.22% and 0.70% vs. 1.22% mb per day); whereas chukars drinking 0.3 M and 0.4 M NaCI lost body mass faster than water-deprived ones (1.75% and 3.62% vs. 1.23% mb per day). This difference in response to saline water intake can be explained, in part, by the difference in drinking rates. Drinking rate in chukars increased with increasing salinity, whereas in sand partridges it progressively decreased. Chukars receiving restricted volumes of saline water lost body mass slower than when allowed to drink the same concentrations ad lib. There was no difference between species in food intake scaled to , but food intake decreased with increasing drinking water salinity in both species. In chukars, assimilated energy as a fraction of gross energy intake decreased at NaCl concentrations above 0.3 M; this occurred at 0.4 M NaCl in sand partridges. In addition, dry matter digestibility and the ash fraction of excreta decreased in chukars when drinking 0.4 M NaCI. The same responses occurred in sand partridges, but only at 0.5 M NaCI. Maximum plasma osmolality was higher in sand partridges than in chukars, but there was no interspecific difference in urine osmolality. We suggest that the better ability of sand partridges to use saline water may partially explain how they are able to inhabit more arid areas than are chukars.