With slugs, at least you can stomp a few of them into paste and gain a pyrrhic victory. Birds? You're the old man and his son in that Simpsons episode shaking your fist at the sky, upset because you can't shake harder.

That being said, 1000s of slugs is practically insurmountable unless you plan to salt the Earth (figurately and literally) or kill the entire neighborhood with fire. Both have...consequences beyond the initial issue. ;)