FEEDING-PATCH CHOICE BY RED DEER IN RELATION TO FORAGING EFFICIENCY -AN EXPERIMENT

We tested the idea that ruminants allocate their feeding time to habit at patches in relation to foraging efficiency. We used five tame red d eer (Cervus elaphus) in an enclosure planted with four treatments of t imothy grass (Phleum pratense) differing in their stage of growth. Old er swards offered higher biomass but lower nutritional quality than yo unger swards. We observed time spent feeding in each treatment during each of seven trials. We measured goodness-of-fit between observed tim es and predictions from two alternative hypotheses differing in optimi zation strategy (maximizing versus matching), and a third, null hypoth esis. We tested the hypotheses using two alternative currencies: diges tible protein, and digestible dry matter or energy. Although digestibl e protein concentration and dry-matter digestibility were highly corre lated (r=0.763, P<0.001), the wider range of digestible protein made i t the much more sensitive measure of forage quality. Distributions of feeding time closely matched estimated intake rates of digestible prot ein (R(Pred)2 d = 0.899) across all animals and trials. The other hypo theses were rejected. The results have important ecological implicatio ns in showing the underlying role of food in the selection of habitat by ruminants, and that simple, mechanistic models of forage intake and digestion can be scaled up to the level of animal behavioural choices .