Unpredictable egg scramble throws off parasitic parents

Some sneaky birds like to shirk their parental duties by slipping their eggs into other birds’ nests. But the birds that host the shysters’ eggs have a trick of their own — scrambling the looks of their eggs so they have distinct signatures.

A look at warbler species, whose nests are infiltrated by the cuckoo finch, and weaver species, whose nests are invaded by the diederik cuckoo, shows that these host birds can lay eggs with colors and markings that are individualistic and hard for parasitic cuckoos to mimic, researchers report June 17 in the Proceedings of the Royal Society B. Eggs of similar bird species whose nests don’t get infiltrated don’t have the same degree of unpredictable patterns, suggesting that defenses against parasitic parents have evolved in these host birds.