Maximizing intake under challenging foraging conditions at two spatial scales in Soay sheep

We examined how decision-making processes at small spatial scales can account for individual movements and food intake at larger scales. Our experiment used two currencies that might affect animal decisions: food reward at the patch scale and spatial distribution of the patches. We used Soay sheep, Ovis aries, as the model species in conjunction with an artificial arena that allowed us to modify food-handling conditions and the distribution of the food patches to record variation in food intake of both sexes. The main variable that affected food intake was how efficient the animals were at avoiding patches that were depleted in previous visits. Intake was also affected by mouth size and the spatial distribution of the feeding stations. Sheep were more efficient at exploiting clustered patches with a high energy reward than a matrix of homogeneously distributed patches of lower energy reward. Females' intake was higher than males'; we discuss this in relation to different foraging strategies related to sexual differences in fibre digestibility and the distribution of food resources of different quality that both sexes might use in field conditions. The results indicated that variation in food-handling conditions at the patch level affects food intake at larger scales, providing support for the hypothesis that animal movement related to grazing activity is a hierarchical process, scaling up from bite size to large spatial scales. However, spatial memory is important for maximizing the use of patchily distributed food.