Common cuckoo lay eggs that better imitate the host's eggs, the host species adapts and is more able to distinguish the cuckoo egg. A study of 248 common cuckoo and host eggs demonstrated that female cuckoos that parasitised common redstart nests laid eggs that matched better than those that targeted dunnocks. Spectroscopy was used to model how the host species saw the cuckoo eggs. Cuckoos that target dunnock nests lay white, brown-speckled eggs, in contrast to the dunnock's own blue eggs. The theory suggests that common redstarts have been parasitised by common cuckoos for longer, and so have evolved to be better
Preening (bird) preening. The conflict between two incompatible drives, such as incubating and escape, can also lead a bird to engage in displacement activities. Nesting Sandwich and common terns preen when they have been alarmed by a potential predator or when they have had an aggressive encounter with a neighboring bird, for instance. Fighting European starlings will break off their battles to preen. Although preening is primarily an individual behaviour, some species indulge in allopreening, with one individual preening another. It is not particularly common among birds, though species from at least 43 families are known to engage in the mutual activity.