Some species of bird are just lazy. So lazy, that they don't even want to take care of their own lazy-ass babies. We call these birds "brood parasites".

To get out of their normal parental duties, these birds lay eggs in the nests of other (non-lazy) birds, and hope for the best. Once these parasitic eggs show up in a nest, the host bird cares for and invests resources in the extra egg. As a result, the "real" eggs in the nest receive less attention and food.

So why would the non-lazy bird (the host) accept eggs that are clearly not her own? The explanation is terrifying: the sneaky lazy birds have evolved to lay eggs that are indistinguishable from the host bird's eggs! Thus, any attempt to destroy the parasite eggs could result in destruction of real eggs, and is not worth the gamble. This is called egg mimicry, and I imagine its a source of constant bullshit for host birds.

In spite of this devious adaptation, host birds are not defenceless. In this month's Trends in Ecology and Evolution (TREE), scientists from New Zealand suggest that some species of Reed Warbler (who are parasitized by the Common Cuckoo, see picture) are able to sometimes end the nightmare of brood parasitism before it gets out of hand.

The host birds manage this by abandoning their nests after a certain time period. At first this seems like a bad idea: what about all the real warbler chicks?! The secret is that warbler chicks have a shorter maturation period than cuckoo chicks. So, after the real chicks are all gone, its just mommy warbler and her weirdly fat cuckoo bastard child.

Although some warblers do end up rearing their unwelcome guest, others (22%) abandon the cuckoo-babe and cut their losses. Even in the face of dastardly adaptations, warblers are able to break the chains of brood parasitism through behavioral evolution. Horray for natural selection!
The article can be found here.