Chukars (Alectoris chukar) and Sand Partridges (Ammoperdix heyi), two ground—dwelling phasianids, are permanent residents of the Negev desert and are sympatric over much of their ranges. Sand Partridges (body mass = 150—250 g), however, inhabit only arid and very arid areas, whereas Chukars (mb = 350—600 g) are widely distributed and inhabit deserts only at the margins of their ranges. We compared some of the desert adaptations of these phasianids by measuring the seasonal field metabolic rates (FMR) and water influxes (using doubly labelled water), diet selection, and food requirements of free—living Chukars and Sand Partridges at a site where both species occurred. Both species showed adaptation in the form of low energy metabolism, which ranged from 43 to 81% of that expected for birds of similar body mass. During summer, Sand Partridges had lower energy expenditures (5.47 kJ°g— ⁰ . ⁶ ¹°d— ¹) and water influxes 72.3 mL°kg— ⁰.⁷ ⁵°d— ¹) than did Chukars (6.42 kJ°g— ⁰ . ⁶ ¹°d— ¹ and 93.5 mL°kg— ⁰ . ⁷ ⁵°d— ¹, respectively), indicating more pronounced adjustments to arid conditions in the desert specialist. However, both species obtained more than half of their water influx in summer by drinking. Their summer diet was relatively dry, consisting mainly of seeds (80%) along with some green vegetation (18%) and, in Chukars, occasional arthropods. This situation changed abruptly after winter rains, which induced germination and reduced the availability of seeds. Chukars were unable to maintain energy balance in the face of low ambient temperatures and a diet (90% green vegetation) that contained much water but comparatively little energy, and they mobilized fat reserves to meet energy requirements. Most Sand Partridges left the study area after winter rains, apparently migrating to the lower elevation, warmer, and drier Arava (part of the Rift Valley). The winter rainy season appears to be the most stressful time of the year for both species. The adaptations to hot, dry conditions possessed by Sand Partridges may be accompanied by constraints on their abilities to cope with cool, wet conditions, and this may restrict them to arid and very arid habitats.

Water organism such as zooplankton fish were used quite often as indicators for water quality in connection with chemically toxic substance in water. Several criteria could be used such as LC50, population index, and physiological phenomena. Bioassay that rely on this physiological phenomena was meant to measure the sublethal effect of the suspected toxic substance on the organisms. Further development of sublethal bioassay using filtering rate of Daphnia carinata (Cooley, 1977; McMahon, 1966) has taken place for a certain detergent. Yeasts cells tagged with P-32 were used as food for Daphnia carinata and the filtering rate was measured from the radioactivity of these crustaceans after a certain period of feeding time. Comparison was made between the feeding rate in the medium with and without the detergent and they appeared to be different.