Estimating predation impact on honeybees Apis mellifera L. by European bee-eaters Merops apiaster L.

We studied predation pressure on honeybees (Apis mellifera L.) by European bee-caters (Merops apiaster L.) in five areas with varying bird and insect populations, on the island of Sardinia (Italy). Number of bee-eater colonies increased with number of food sources (hives and apiaries); conversely total bird population and colony size were not related to food sources. Bee-caters preyed on bees (foragers) in relation to their mean total availability (calculated over all study areas), but predation on bees occur-red also where hives were absent or far away. By contrast, predation on drones was negatively correlated to their mean total availability. Indeed, predation on foragers and drones correlated negatively. Predation impact on foragers was on average 0.37% (range: 0.26-0.58%) of their mean total availability during May-July. The daily forager mortality per hive due to bee-eater predation represented on average 6.1% (n = 73) of their total daily mortality per hive. Predation pressure on drones was on average 0.91% (range: 0.27-1.43%) of their mean total availability during May-July. The daily drone mortality per hive due to bee-cater predation represented on average 30% (n = 4) of their total daily mortality per hive. Predation impact by bee-eaters on foragers was independent from prey density. Conversely, predation on drones was inversely dependent from prey density, thus it was diluted at high hive densities. The economic impact on apiculture by bee-caters was in general negligible, but losses of drones were locally important and potentially detrimental to small or specialized apicultures