Cuckoo Birds in an "Evolutionary War"

Here's an interesting piece from io9:

Cuckoos don't bother building their own nests - they just lay eggs that perfectly mimic those of other birds and take over their nests. But other birds are wising up, evolving some seriously impressive tricks to spot the cuckoo eggs. 

Cuckoos are what's known as brood parasites, meaning they hide their eggs in the nests of other species. To avoid detection, the cuckoos have evolved so that their eggs replicate those of their preferred targets. If the host bird doesn't notice the strange egg in its nest, the newly hatched cuckoo will actually take all the nest for itself, taking the other eggs on its back and dropping them out of the nest. 

 To avoid this nasty fate for their offspring, the other birds have evolved a few nifty ways to spot the fakes, which we're only now beginning to fully understand. One of the most intriguing finds is that birds have an extra color-sensitive cell in their retinas, which makes them far more sensitive to ultraviolet wavelengths and allows them to see a far greater range of colors than we humans can. This allows wary birds to detect a counterfeit egg where to our eyes they're all identical...