Data from: Brood parasites lay eggs matching the appearance of host clutches

Interspecific brood parasitism represents a prime example of the
co-evolutionary arms race where each party has evolved strategies in
response to the other. Here we investigated whether common cuckoos
(Cuculus canorus) actively select nests within a host population to match
the egg appearance of a particular host clutch. To achieve this goal, we
quantified the degree of egg matching using the avian vision modelling
approach. Randomization tests revealed that cuckoo eggs in naturally
parasitized nests showed lower chromatic contrast to host eggs than those
assigned randomly to other nests with egg-laying date similar to naturally
parasitized clutches. Moreover, egg matching in terms of chromaticity was
better in naturally parasitized nests than it would be in the nests of the
nearest active non-parasitized neighbour. However, there was no indication
of matching in achromatic spectral characteristics whatsoever. Thus, our
results clearly indicate that cuckoos select certain host nests to
increase matching of their own eggs with host clutches but only in
chromatic characteristics. Our results implicate that the ability of
cuckoos to actively choose host nests based on the eggshell appearance
imposes a strong selection pressure on host egg recognition.