There seem to be limitless examples of how nature takes advantage of changing environments in order to exploit smaller, weaker, more easy-going members of its society. I'm sad to tell you that it also happens in the bird world.
Used to be, cowbirds hung out with the buffalo and followed them around, taking advantage of the insect explosion stirred up by the wandering herd. Since the big beasts moved around a lot, so did the cowbirds; in fact, they never stayed in one place long enough to build nests. So what did they do? Why, they used other birds' nests as their own little incubation system. And they still do it.
(If you don't believe me, you can read about it here or here. Appalling, isn't it?)
You can see why we aren't big cowbird fans; we know what they're up to, laying their big, nasty eggs in the nests of smaller, unsuspecting birds, to the detriment and even death of the host birds' own young. And when those cowbirds show up at our bird feeder, we scare them away. We clap at them, shout at them, even open the door and run at them until they flee in fear, their annoyingly high-pitched call echoing behind them as they vacate the premises.
But honestly, how much good does it do? They keep showing up. They've found a way to use and abuse the good, upstanding members of Birdville, and they're going to keep at it until somebody is defeated or disappears. Worst of all, the cowbirds aren't going anywhere because the constant destruction of forest and opening up of more woodland edges actually exacerbate the problem; that's just the sort of surroundings to which they flock.
We'll keep on fighting the good fight. And yet... it's feeling like a lost cause, because even as I type, Mama Cowbird is out there laying roughly an egg a day, invading as many happy homes as possible, dooming the rightful members of the family.
The worst part is that our own society is looking a lot like nature these days. Sigh.