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The Chukar subspecies Alectoris chukar sinaica inhabits the Negev desert, which is characterized by hot, dry summers, and little winter rainfall. Vegetation is dry and dormant during the summer and autumn; green, succulent vegetation is available following winter rain. We studied whether or not and under what dietary conditions Chukars require drinking water. Four groups of Chukars in an outdoor aviary received either a dry ration + water, a dry ration + green vegetation, a dry ration + green vegetation + water, or green vegetation only. The birds offered only greens lost 15% of their body mass in the first 8 days and 2.9% over the next 6 days, while birds on the other three treatments maintained body mass. The birds receiving only greens had the highest total body water to body mass ratio and the highest water influx. We concluded that the Chukars receiving only green vegetation met their water requirements but not their maintenance energy requirements. Chukars fulfilled both their water and energy requirements on a dry ration + green vegetation (without drinking water); the green vegetation comprised approximately 60% of their total fresh matter intake, or 26% of their total dry matter intake. Our analysis suggests that wild desert Chukars do not require drinking water from early winter to late spring, when succulent forage is available, but probably need free water during summer and autumn, when the bulk of their diet is seeds.

Purpose This study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency. Methods Laboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing. Results The observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%). Conclusion The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency.