Natural predators are cheaper. In fact, border collies and peregrine falcons have been particularly good at keeping birds at bay on airfields. But they are useless without skilled handlers.

• 天然食肉动物更廉价。实际上，博德牧羊犬和游隼在使鸟不靠近飞机场上效果特别好。但是没有熟练地训练员，它们是没有用的。