THE EFFECT OF DEPLETION AND PREDICTABILITY OF DISTINCT FOOD PATCHES ON THE TIMING OF AGGRESSION IN RED DEER STAGS

For group-foraging ungulates, forage is generally widely and relativel y evenly dis persed. However, for free-ranging red deer Cervus elaphus supplementary winter feeding provides distinct patches of predictable food. These patches differ in size, but also in temporal distribution and depletion rate. Interference competition is known to increase wit h increasing spatial clumping (decreasing patch size), but the influen ce of temporal clumping and the predictability of food occurrence has received much less attention. Therefore in this study we investigated the effects of different degrees of spatial and temporal clumping of f ood on interference competition during feeding. Patch size was the mai n parameter influencing participation in feeding as well as interferen ce competition during feeding on the respective patch. Temporal disper sion and the predictability of food occurrence were however, important parameters for the timing of aggressive interactions. Generally, aggr ession occurs during feeding and increases with decreasing patch size. But when depletion rate was high, food availability was predictably s hort and the patch occurred predictably (such as hay), middle ranking stags increased aggression already prior to feeding at the respective patch. We suggest that in this way they confirmed hierarchy outside fe eding on the quickly depleted patch and as a result gained actual feed ing time when feeding on the respective patch. With the patch occurrin g predictably but varying in size, the number of participating subordi nates varied concomitantly with variation in patch size. Subordinates assessed patch profitability and left without having fed when patch si ze was too small for an efficient participation. When patch size was p redictably small enough to be defended exclusively (feed blocks), subo rdinate stags did not assess profitability each time but did not parti cipate at all in feeding at the respective patch. The relative importa nce of these various food-related parameters (patch size, depletion ra te, predictability) influencing feeding competition and the timing of aggression will vary with group size, rank, alternative food sources, physical characteristics of the food as well as different hierarchy sy stems of the feeding animals.