Providing water for goats in arid landscapes: effects on feeding effort with regard to time period, herd size and secondary compounds

In arid regions, herbivores contend with a wide range of variables that influence their foraging ability. These may include plant secondary compounds (e.g. tannins and oxalates), water availability, time of day, and herd size. To determine the relative importance of these variables for goats living in a semi-desert, we measured the remaining food resources after foraging events (giving up densities-GUDs) as an index of foraging effort in artificial food patches. Time of day and the availability of drinking water had the greatest effect on GUDs. Goats achieved lower GUDs (i.e. ate more) in the afternoon than they did during the morning. We suggest this was due to missed opportunity costs of future foraging opportunities being lower in the afternoon. Ultimately, this implies that goats made short-term foraging decisions based on estimates of future feeding opportunities. When water was available, feeding effort increased and GUDs dropped almost 50%. For goats living in an arid environment, food and water are strong complementary resources. The presence of low to moderate levels of tannic or oxalic acid in food was a slight deterrent, raising the GUDs similarly. Larger herds ate more and thus obtained lower GUDs. In addition, there was an interaction of herd size and water, suggesting that in arid environments, the effect of water intensifies with population density. Our approach allowed us to quantify and rank the effects that disparate environmental factors had on the goats' foraging costs: water > time of day > herd size > plant secondary compounds. These findings ultimately demonstrate how the provision of water may increase grazing impacts by herbivores in arid landscapes.