Seed removal by birds and its association with grazing intensity and vegetation in the central Monte desert

Seeds are a crucial stage in the dynamics of vegetation in arid zones and a food resource for granivorous organisms. The posdispersive consumption of seeds can be separated into two components: the number of points that are visited to search for seeds (exploration) and the amount of seeds consumed in each one (exploitation). We hypothesize that there are changes in the seed consumption activity of the granivorous birds in association with their abundance, the abundance of resources and their modification by grazing, and the accessibility to feeding points given by the structure of the perennial vegetation. We experimentally evaluated both components of consumption by offering individual seeds and trays of seeds along transects in the central Monte desert, near General Alvear, Mendoza, Argentina. The results suggest that seed consumption varies in association with vegetation structure (coverage and height of different strata and presence of trees). The exploration of feeding points was positively correlated with the abundance of birds and with the number of trees, and was negatively correlated with the cover of low shrubs. Exploitation was also positively correlated with the number of trees. The measured variables of grazing intensity (cattle load and grass cover) were not directly related to consumption. However, when considering the variation of bird abundances among transects, we found that exploration intensity per bird is higher when grass cover is low.