The use of spatial memory by grazing animals to locate food patches in spatially heterogeneous environments: An example with sheep

The ability of sheep to remember the spatial location of food patches was examined in two experiments. In the first experiment, patches (plastic bowls) were laid out on a grass field and some of the patches were randomly assigned to contain food (sheep pellets), Individual sheep were released into the field on a number of occasions and on each occasion the number of patches visited until all the patches that contained food had been located was recorded, Sheep were tested at three levels of complexity: one food patch among eight total patches laid out in a horizontal array; two food patches among 16 total patches laid out in a 8 x 2 grid; four food patches among 32 total patches laid out in a 8 x 4 grid. All patches were 5 m apart. Twenty sheep were tested in the one in eight level and ten sheep in the two more complex levels, At all levels of complexity, sheep returned to the patches that contained food, 12 h after first exposure, at a level better than that expected if they had searched at random, After six exposures to the distribution of patches, at 12 h intervals, sheep visited the food patches almost exclusively. The performance of the sheep did not decline when the time between successive visits was increased to 72 h. In the second experiment, individual sheep searched for one patch that contained food among eight total patches laid in a horizontal array on a grass field, Ten animals were tested with a cue (turf of white clover) located behind the food patch, and ten animals without. A wire mesh cage was placed over the top of the cue so that it could be seen and smelled, but not eaten. Sheep learned the location of the food patch with and without cues, but learned faster when a cue was present, When the location of the cue and food patch was switched randomly between trials, the sheep used spatial memory first and went to where the food patch had previously been located, but on finding no food used associations between the cue and food patch to eo to the new food patch location. The ability to use spatial memory and associations between cues and rewards would help sheep to increase the rate at which they encounter preferred food patches, and to exploit spatial heterogeneity in the food resource better.